WO2025054733A1

WO2025054733A1 - Lignin-derived hard carbons and methods of use thereof

Info

Publication number: WO2025054733A1
Application number: PCT/CA2024/051222
Authority: WO
Inventors: John Frank KADLA; James Ian DALLMEYER
Original assignee: Suzano Canada Inc
Current assignee: Suzano Canada Inc
Priority date: 2023-09-15
Filing date: 2024-09-13
Publication date: 2025-03-20
Anticipated expiration: 2026-03-15

Abstract

Coated hardwood lignin-derived hard carbon particles for use in an electrode active layer of an electrode are provided. The coated particles are prepared by a process including thermal pretreatment, oxidative stabilization, pyrolysis, carbonization and ethylene treatment. The coated particles are for use as an electrode active layer for an anode, such as in a lithium ion battery or a sodium ion battery.

Description

LIGNIN-DERIVED HARD CARBONS AND METHODS OF USE THEREOF

FIELD OF THE INVENTION

[0001] The present disclosure provides lignin-derived hard carbon particles. More specifically, the present disclosure provides hardwood lignin-derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of a hydrocarbon, for use in an electrode active layer of a battery system.

BACKGROUND OF THE INVENTION

[0002] With increased focus on the use of renewable energy systems, there is a need for the development of improved energy storage systems. For example, modern technologies require improvements in battery pack specific energies and energy densities at lower costs. Materials for batteries must combine high performance with low-cost, and must be processed using industrially scalable methods. Lithium ion batteries are currently considered as one of the key technologies for energy storage, with applications in many different devices. Graphite is the predominant anode material used in commercial lithium ion batteries due to favourable electrochemical performance, but hard carbons can also be used, particularly in situations where fast charging is desired. Hard carbon has been used as an anode for sodium ion batteries, while graphite is unsuitable as an anode active material in these battery systems. While advances in lithium ion battery manufacturing have reduced their cost over time, the availability of critical minerals is a barrier to further cost reduction. It has also been increasingly recognized that replacing mineral- and petroleum-derived carbon materials with bio-derived carbons is preferable in terms of sustainability. Limitations to graphite anodes pertain to their cycling stability under fast charge conditions, and their suitability for use in newly emerging sodium ion batteries, while limitations to hard carbon pertain to their first-cycle coulombic efficiency, voltage hysteresis and reversible capacity.

[0003] Lignins are a heterogeneous class of complex cross-linked organic polymers. They form a relatively hydrophobic and aromatic phenylpropanoid complement to cellulose and hemicellulose in the structural components of vascular plants. Lignification is the final stage in plant cell wall development, lignin serving as the ‘adhesive’ consolidating the cell wall. As such, native lignin has no universally defined structure. Native lignin is a complex macromolecule comprised of 3-primary monolignols (e.g. phenylpropane units: p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol) connected through a number of different carbon-carbon and carbon-oxygen linkages. The type of monolignol and inter-unit linkage vary depending on numerous factors including genetic and environmental factors, species, cell/growth type, and location within/between the cell wall.

[0004] Extracting lignin from lignocellulosic biomass generally results in lignin deconstruction/modification and generation of numerous lignin fragments of varying chemistry and macromolecular properties. Some processes used to remove lignin from biomass hydrolyse the lignin structure into lower molecular weight fragments with high amounts of phenolic hydroxyl groups, thereby increasing their solubility in the processing liquor (e.g. sulphate lignins). Other processes not only deconstruct the lignin macromolecule, but also introduce new functional groups into the lignin structure to improve solubility and facilitate their removal (e.g. sulphite lignin). The generated lignin fragments are generally referred to as lignin derivatives and/or technical lignins. As it is quite difficult to elucidate and characterize such complex mixtures of molecules and macromolecules, lignin derivatives are usually described in terms of the lignocellulosic plant material used, and the methods by which they are produced and recovered from, i.e. lignin isolated from the Kraft pulping of a softwood species is referred to as softwood Kraft lignin. Likewise, the organosolv pulping of an annual fibre generates an annual fibre organosolv lignin, etc.

[0005] Despite lignins being among the most abundant natural polymers on earth, the large-scale commercial use of extracted lignin derivatives isolated from traditional pulping processes used in the manufacture of pulp for paper manufacturing has been limited. This is due not only to the important role lignins and lignin-containing processing liquors play in process chemical/energy recovery, but also due to the inherent inconsistencies in their chemical and physical properties. These inconsistencies can arise due to numerous factors, such as changes in biomass supply (region/time of year/climate) and the particular extraction/generation/recovery conditions employed, which are further complicated by the inherent complexities in the chemical/molecular structures of the biomass itself.

[0006] Notwithstanding their complexity, lignins continue to be evaluated for a variety of carbonaceous materials. For example, electrodes may be produced from lignin-based hard carbons due to the high carbon content and aromatic structure of lignins for lithium ion batteries (see, for example, Tenhaeff, W.E., et al. (2014) Adv. Funct. Mater., 24, 86- 94 and Garcia-Negron, V., et al. (2017) Energy Tech., 5(8), 1311 -1321 ) and sodium ion batteries (see, for example, Lin, X., et al. (2020), Carbon, 157, 316-323). Organosolv lignins have been used to produce electrodes for sodium ion batteries with high reversibility, based on the high purity of these lignins (see, for example, Irisarri, E., et al. (2018) J. Electrochem. Soc., 165(16), A4058-A4066). Organosolv lignins have low ash content and do not contain sulfur. Kraft softwood lignins have also been investigated for this application. More specifically, Ghimbeu, C. M., et al. (2019) Carbon, 153, 634-647 disclose lignin kraft and lignin sulphonate as precursors for the preparation of hard carbon anodes for sodium ion batteries that had an initial irreversible capacity of 33.7% to 21 .9% and a reversible capacity of 205 to approximately 300 mAhg’¹.

[0007] However, there remains a need for lignin-based hard carbon battery anode active materials which combine high reversible capacity, high first-cycle coulombic efficiency, high capacity retention at high charging currents, and/or low charge-discharge voltage hysteresis.

SUMMARY OF THE INVENTION

[0008] Various aspects of the present disclosure provide compositions for use as an electrode active layer, the composition comprising hardwood lignin-derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of a hydrocarbon, a binder and a conductivity additive, wherein a ratio of the hardwood lignin- derived hard carbon particles : the binder : the conductivity additive is between 80:10:10 and 99:1 :1.

[0009] In various embodiments, the composition is for application to a current collector as a slurry to form an electrode.

[0010] In various embodiments, the hardwood lignin is a hardwood Kraft lignin. [0011] In various embodiments, an electrode active layer of an anode comprises a composition as defined herein.

[0012] In various embodiments, an electrochemical cell comprises a composition as defined herein as part of an electrode active layer of an anode of the electrochemical cell. [0013] In various aspects, the present disclosure provides a method for preparing coated hardwood lignin-derived hard carbon particles from a hardwood lignin, the method comprising the following steps: thermal pretreatment comprising extrusion or baking of the hardwood lignin under inert atmosphere or vacuum at temperatures of about 300°C to about 400°C within a time of between about 10 seconds and about 2 hours to form a pretreated lignin; oxidative stabilization comprising baking the pretreated lignin in air at a temperature between about 200°C and about 250°C within a time of between about 10 seconds and about 3 hours to form a stabilized lignin; pyrolysis comprising heating the stabilized lignin in an inert atmosphere at a temperature between about 600°C and about 700°C within a time of about 0.1 hours to about 8.5 hours to form a pyrolysed lignin; carbonization comprising heating the pyrolysed lignin in an inert atmosphere at a temperature between about 1000°C and about 1600°C within a time of about 0.1 and about 36 hours to form hard carbon particles; and hydrocarbon treatment comprising heating the hard carbon particles in a mixed atmosphere of argon and a hydrocarbon at a temperature between about 800°C and about 1000°C within a time of about 0.1 hours and about 6 hours to form the coated hardwood lignin-derived hard carbon particles, the hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of the hydrocarbon.

[0014] In various embodiments, the hardwood lignin derivative is a hardwood Kraft lignin.

[0015] In various embodiments, the hydrocarbon is ethylene.

[0016] In various embodiments, the method further comprises: (a) size reduction of the hard carbon particles prior to the hydrocarbon treatment, and/or (b) classification of the hard carbon particles before or after the hydrocarbon treatment to a particle size distribution between about 1 micron and about 40 microns. For example, the size reduction may be done after thermal treatment, after pyrolysis or after carbonization. For example, the classification may be done before or after the hydrocarbon treatment. [0017] In various embodiments, the method further comprises washing the hard carbon particles with an aqueous acid prior to the hydrocarbon treatment. For example, the aqueous acid may be hydrochloric acid, hydrofluoric acid, sulfuric acid, or nitric acid. [0018] In various embodiments, the method further comprises one or more purification steps prior to the hydrocarbon treatment. For example, the hardwood lignin may be purified prior to the thermal pretreatment step. For example, the pretreated lignin may be purified prior to the oxidative stabilization step. For example, the stabilized lignin may be purified prior to the pyrolysis step. For example, the pyrolysed lignin may be purified prior to the carbonization step. For example, the hard carbon particles may be purified prior to the hydrocarbon treatment.

[0019] In various aspects, the present disclosure provides coated hardwood lignin- derived hard carbon particles produced according to a method as described herein. The coated hardwood lignin-derived hard carbon particles may be for use as an electrode active layer for an electrode. For example, the coated hardwood lignin-derived hard carbon particles may be for use as the electrode active layer for an anode. For example, the coated hardwood lignin-derived hard carbon particles may be for use as the electrode active layer for an anode in a lithium ion battery or in a sodium ion battery.

[0020] In various aspects, the present disclosure provides an electrode comprising a current collector coated with hardwood lignin-derived hard carbon particles produced according to a method as described herein, a binder, and a conductivity additive, wherein a ratio of the hardwood lignin-derived hard carbon particles : the binder : the conductivity additive is between 80: 10: 10 and 98: 1 : 1 .

[0021] In various embodiments, the binder is polyvinylidene difluoride.

[0022] In various embodiments, the conductivity additive is C65 conductive carbon black.

[0023] In various embodiments, the current collector is a copper foil.

[0024] In various aspects, the present disclosure provides coated hardwood lignin- derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a total reversible lithiation capacity of greater than or equal to 360 mAh per gram (mAhg^-1) and hysteresis area less than or equal to 162 J per gram (Jg^-1) when tested in a half cell configuration against lithium metal, wherein hysteresis area is measured as the area of a de-lithiation profile (V versus capacity in Coulombs per gram (Cg^-1)) minus the area of a lithiation profile, wherein the electrode for measurement is a copper foil coated with hardwood lignin- derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black, in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M lithium hexafluorophosphate (LiPFe) dissolved in a 1 :1 :1 (v/v) mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate.

[0025] In various aspects, the present disclosure provides coated hardwood lignin- derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a total reversible lithiation capacity of greater than or equal to 290 mAh per gram (mAhg’¹) and a hysteresis area less than or equal to 113 J per gram (Jg^-1) when tested in a half cell configuration against lithium metal, wherein the hysteresis area is measured as the area of a de-lithiation profile (V versus capacity in Coulombs per gram (Cg^-1)) minus the area of a lithiation profile, wherein the electrode for measurement is a copper foil coated with hardwood lignin- derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black, in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M lithium hexafluorophosphate (LiPFe) dissolved in a 1 :1 :1 (v/v) mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate.

[0026] In various aspects, the present disclosure provides coated hardwood lignin- derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a total reversible lithiation sloping capacity of greater than or equal to 310 mAh per gram (mAhg-¹), a reversible lithiation plateau capacity of greater than or equal to 50 mAhg^-1, and a hysteresis area less than or equal to 162 J per gram (Jg^-1) when tested in a half cell configuration against lithium metal, wherein the lithiation sloping capacity is defined as the reversible capacity obtained under constant current conditions at 30 mA per gram and the lithiation plateau capacity is defined as the reversible capacity obtained under constant voltage conditions greater than 0 and less than 0.1 mV versus Li/Li⁺, wherein the electrode for measurement is a copper foil coated with hardwood lignin-derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black, in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M lithium hexafluorophosphate (LiPFe) dissolved in a 1 :1 :1 (v/v) mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate. [0027] In various aspects, the present disclosure provides coated hardwood lignin- derived hard carbon particles for use in an electrode, wherein the electrode comprising the hardwood lignin-derived hard carbon particles has a total reversible lithiation sloping capacity of greater than or equal to 240 mAh per gram (mAhg^-1), a reversible lithiation plateau capacity of greater than or equal to 50 mAhg^-1, and a hysteresis area less than or equal to 113 J per gram (Jg^-1) when tested in a half cell configuration against lithium metal, wherein the lithiation sloping capacity is defined as the reversible capacity obtained under constant current conditions at 30 mA per gram and the lithiation plateau capacity is defined as the reversible capacity obtained under constant voltage conditions greater than 0 and less than 0.1 mV versus Li/Li⁺, wherein the electrode for measurement is a copper foil coated with hardwood lignin-derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black, in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M lithium hexafluorophosphate (LiPFe) dissolved in a 1 :1 :1 (v/v) mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate.

[0028] In various aspects, the present disclosure provides coated hardwood lignin- derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a reversible lithiation capacity greater than or equal to twice the reversible capacity of a graphite comparison electrode when measured at a current density of 300 mAg^-1 when tested in a half cell configuration against lithium metal, wherein the electrode for measurement is a copper foil coated with hardwood lignin-derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M lithium hexafluorophosphate (LiPFe) dissolved in a 1 :1 :1 (v/v) mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate, and the graphite comparison electrode does not comprise hardwood lignin-derived hard carbon particles.

[0029] In various aspects, the present disclosure provides coated hardwood lignin- derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a first-cycle coulombic efficiency of greater than or equal to 85% when tested in a half cell configuration against lithium metal, wherein the electrode for measurement is a copper foil coated with hardwood lignin-derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black, in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M lithium hexafluorophosphate (LiPFe) dissolved in a 1 :1 :1 (v/v) mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate.

[0030] In various aspects, the present disclosure provides coated hardwood lignin- derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a first-cycle coulombic efficiency of greater than or equal to 82% and a reversible sodiation capacity of greater than or equal to 280 mAhg^-1 when tested in a half cell configuration against sodium metal with a constant current-constant voltage (CC-CV) cycling protocol consisting of a constant current portion with current density of 30 mAg’¹, applied until the voltage drops to 0.01 V versus Na/Na⁺ and followed by a constant voltage portion applied until the current density drops to 6mAg’¹, wherein the electrode for measurement is a copper foil coated with hardwood lignin-derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M sodium perchlorate (NaCIO4) dissolved in a 1 :1 (v/v) mixture of ethylene carbonate and diethyl carbonate with the addition of 2% fluoroethylene carbonate as an electrolyte additive.

[0031] In various aspects, the present disclosure provides coated hardwood lignin- derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a first-cycle coulombic efficiency of greater than or equal to 82%, a reversible sloping sodiation capacity of greater than or equal to 76 mAhg^-1, and a reversible plateau sodiation capacity of greater than or equal to 204 mAhg^-1, when tested in a half cell configuration against sodium metal with a constant current-constant voltage (CC-CV) cycling protocol consisting of a constant current portion with current density of 30 mAg’¹, applied until the voltage drops to 0.01 V versus Na/Na⁺ and followed by a constant voltage portion applied until the current density drops to 6 mAg^-1, with sloping capacity defined as corresponding to sodiation occurring about 0.1 V versus Na/Na⁺, plateau capacity defined as corresponding to sodiation occurring about 0 V and less than 0.1 V versus Na/Na⁺, and wherein the electrode for measurement is a copper foil coated with hardwood lignin-derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M sodium perchlorate (NaCICM) dissolved in a 1 :1 (v/v) mixture of ethylene carbonate and diethyl carbonate with the addition of 2% fluoroethylene carbonate as an electrolyte additive.

[0032] In various embodiments, the hardwood lignin is a hardwood Kraft lignin.

[0033] In various embodiments, the particles are a powder. For example, a particle size distribution of the particles may be between about 1 micron and about 40 microns.

[0034] In various embodiments, the present disclosure provides an anode comprising coated hardwood lignin-derived hard carbon particles as defined herein as an electrode active layer. For example, an electrochemical cell may comprise coated hardwood lignin- derived hard carbon particles as described herein as part of an electrode active layer of an anode of the electrochemical cell.

[0035] Other aspects and features of the present invention will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In drawings which illustrate embodiments of the disclosure,

[0037] Figure 1 shows average lithiation capacity (mAhg^-1) as a function of cycle number for an electrode comprising coated hardwood lignin-derived hard carbon particles according to an embodiment of the disclosure (grey circles) as compared to an electrode coated with hardwood lignin-derived hard carbon particles not coated with pyrolytic carbon derived from thermal decomposition of a hydrocarbon (black circles) in a lithium half cell cycled at 30, 60, 150 300 and 30 mAg’¹.

[0038] Figure 2 shows potential and current as a function of time during the 25th cycle of a lithium/hard carbon half-cell, the lithium/hard carbon half-cell comprising coated hardwood lignin-derived hard carbon particles according to an embodiment of the disclosure as a component of the anode.

[0039] Figure 3 shows cell potential as a function of normalized capacity of a lithium/hard carbon half-cell at cycle number 25 with areal active mass loading of 5.7 mg/cm², the lithium/hard carbon half-cell comprising coated hardwood lignin-derived hard carbon particles according to an embodiment of the disclosure as a component of the anode. The shaded area in Figure 3 represents the hysteresis quantified in units of C/g. [0040] Figure 4 shows potential and current as a function of time during the 10th cycle of a sodium/hard carbon half-cell, the sodium/hard carbon half-cell comprising coated hardwood lignin-derived hard carbon particles according to an embodiment of the disclosure as a component of the anode.

[0041] Figure 5 shows cell potential as a function of normalized capacity of a sodium/hard carbon half-cell at cycle number 10 with areal active mass loading of 4.6 mg/cm², the sodium/hard carbon half-cell comprising coated hardwood lignin-derived hard carbon particles according to an embodiment of the disclosure as a component of the anode.

DETAILED DESCRIPTION

[0042] In the context of the present disclosure, various terms are used in accordance with what is understood to be the ordinary meaning of those terms.

[0043] In various embodiments, the disclosure provides coated hardwood lignin- derived hard carbon particles for use in an electrode. The lignin-based hard carbon particles as described herein are battery anode active materials which combine high reversible capacity, high first-cycle coulombic efficiency, high capacity retention at high charging current, and/or low charge-discharge voltage hysteresis. [0044] Lithium and sodium ion batteries are types of rechargeable batteries which use the reversible reduction of lithium ions or sodium ions, respectively, to store energy. The components of these batteries are cathode, anode and electrolyte, which work via the transport of lithium or sodium ions during charging and discharging processes. Thus, the term “lithiation” describes the process where lithium ions diffuse to and react with an electrode and “de-lith iation” describes the process where lithium ions leave an electrode. Lithiation and de-lithiation reactions result in energy loss, and the energy lost in one cycle of lithiation and de-lithiation reactions may be determined by the hysteresis area on a plot of cell potential as a function of normalized capacity for a lithiation reaction and a de- lithiation reaction at an electrode. The term “sodiation” describes the process where sodium ions diffuse to and react with an electrode and “de-sodiation” describes the process where sodium ions leave an electrode. Sodiation and de-sodiation reactions result in energy loss, and the energy lost in one cycle of sodiation and de-sodiation reactions may be determined by the hysteresis area on a plot of cell potential as a function of normalized capacity for a sodiation reaction and a de-sodiation reaction at an electrode. [0045] The performance of rechargeable batteries generally depends on the conductivity of the electrodes. The electrochemical potential of an electrode material is correlated with the energy required to add or move lithium or sodium ions from the electrode. The capacity for an electrochemical reaction is the quantity of electricity involved in that reaction. In the present disclosure, hardwood lignin-derived hard carbons are used as an anodic material due to their ability for storing lithium ions or sodium ions, including their large surface area, high conductivity and charge carrier mobility, as compared to other known anodic materials such as graphite. Performance and efficiency of a rechargeable battery can be measured through a number of parameters. For example, “coulombic efficiency” describes the efficiency by which charges are transferred in batteries. Coulombic efficiency is the ratio of the total charge extracted from the battery to the total charge put into the battery over a full cycle. The first-cycle coulombic efficiency is an important measurement of the first formation of the electrochemical cell as capacity of the cell is lost due to reactions between ions, electrolyte solvents, salts and the anode material, resulting in irreversible lithium or sodium consumption at the anode. [0046] The present disclosure provides coated hardwood lignin-derived hard carbon particles for use in an electrode, such as, for example, an anode. The hardwood lignin is recovered from a pulping process of lignocellulosic hardwood feedstocks, such as, for example, Kraft hardwood lignin. The “electrode” in an electrochemical cell, half cell or battery as described herein consists of an electrode active layer coated over a current collector. The coated hardwood lignin-derived hard carbon particles as disclosed herein are part of the electrode active layer, together with a binder and/or a conductivity additive, as described in further detail below. Therefore, the electrode active layer is a composite system of the coated hardwood lignin-derived hard carbon particles, and the binder and/or the conductivity additive. The current collector of the lithium ion electrodes as described herein may be a copper foil, amongst other examples which would be known to a person of ordinary skill in the art. The current collector of the sodium ion electrodes as described herein may be aluminum or copper, amongst other examples which would be known to a person of ordinary skill in the art. Aluminum cannot be used as a current collector in a lithium ion electrode as the aluminum can alloy with lithium and result in capacity fading. [0047] The hardwood lignin-derived hard carbon particles are coated with pyrolytic carbon derived from thermal decomposition of a hydrocarbon. For example, the hardwood lignin-derived hard carbon particles may be coated with pyrolytic carbon derived from thermal decomposition of ethylene. Further examples of hydrocarbons for coating the hardwood lignin-derived hard carbon particles with pyrolytic carbon are alkanes, alkenes, alkynes, or aromatic compounds. For example, various hydrocarbons may comprise methane, ethane, propane, butane, pentane, propylene, butylene, acetylene, propyne, butyne, benzene, toluene or any combination thereof (see, for example, US Patent Application Publication No. 2023/0041090 and US Patent No. 6,143,268).

[0048] As the electrode active layer, the coated hardwood lignin-derived hard carbon particles may be used in combination with a binder and/or a conductivity additive. For example, the binder may be polyvinylidene difluoride. The binder may also be styrenebutadiene rubber (SBR), sodium carboxymethylcellulose (Na-CMC), and/or polyacrylates such as poly(acrylic acid) and sodium polyacrylate. For example, the conductivity additive may be a conductive grade of carbon black. For example, the conductivity additive may be C65 conductive carbon black. The conductivity additive may also be a carbon nanotube, graphene, and/or carbon nanofibers.

[0049] The ratio of the coated hardwood lignin-derived hard carbon particles : binder : conductivity additive may be 80:10:10, or any higher ratio of coated hardwood lignin- derived hard carbon particles up to 99%. For example, the ratio of the coated hardwood lignin-derived hard carbon particles : binder : conductivity additive may be between 80: 10: 10 to 98: 1 : 1 or any ratio therebetween. The ratio may be 80: 10:10. The ratio may be 82:9:9. The ratio may be 84:8:8. The ratio may be 86:7:7. The ratio may be 88:6:6. The ratio may be 90:5:5. The ratio may be 92:4:4. The ratio may be 94:3:3. The ratio may be 96:2:2. The ratio may be 98:1 :1. The ratio may be 90:4:6. The ratio may be 90:6:4. The ratio may be between 80 wt% - 99 wt% coated hardwood lignin-derived hard carbon particles, 1 wt% - 10 wt% binder, and 1 wt% - 10 wt% conductivity additive.

[0050] In various embodiments, the hardwood lignin-derived hard carbon is in the form of a particle. The particles may be a powder with a particle size distribution of between about 1 micron and about 40 microns. The particles may have this size distribution either before or after coating with pyrolytic carbon derived from thermal decomposition of a hydrocarbon. For example, the particle size distribution of the particles may be between about 1 micron and about 20 microns. For example, the particle size distribution of the particles may be between about 1 micron and about 10 microns. For example, the particle size distribution of the particles may be between about 1 micron and about 30 microns. For example, the particle size distribution of the particles may be between about 5 microns and about 15 microns. For example, the particle size distribution of the particles may be between about 5 microns and about 20 microns. For example, the particle size distribution of the particles may be between about 5 microns and about 30 microns. For example, the particle size distribution of the particles may be between about 5 microns and about 40 microns. For example, the particle size distribution of the particles may be between about 10 microns and about 20 microns. For example, the particle size distribution of the particles may be between about 10 microns and about 30 microns. For example, the particle size distribution of the particles may be between about 10 microns and about 40 microns. For example, the particle size distribution of the particles may be between about 15 microns and about 30 microns. For example, the particle size distribution of the particles may be between about 15 microns and about 40 microns. For example, the particle size distribution of the particles may be between about 20 microns and about 30 microns. For example, the particle size distribution of the particles may be between about 20 microns and about 40 microns. For example, the particle size distribution of the particles may be between about 30 microns and about 40 microns. Particles of these size distributions ensure that suitable slurries can be formed for purposes of coating the current collector. Furthermore, particles of this size provide the desired balance of power and energy in the battery or half-cell.

[0051] The present disclosure provides coated hardwood lignin-derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a total reversible lithiation capacity of greater than or equal to 360 mAh per gram (mAhg-¹) and hysteresis area less than or equal to 162 J per gram (Jg^-1) when tested in a half cell configuration against lithium metal, wherein hysteresis area is measured as the area of a de-lithiation profile (V versus capacity in Coulombs per gram (Cg^-1)) minus the area of a lithiation profile, wherein the electrode for measurement is a copper foil coated with hardwood lignin-derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M lithium hexafluorophosphate (LiPFe) dissolved in a 1 :1 :1 (v/v) mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate.

[0052] The present disclosure provides coated hardwood lignin-derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a total reversible lithiation capacity of greater than or equal to 290 mAh per gram (mAhg^-1) and a hysteresis area less than or equal to 113 J per gram (Jg^-1) when tested in a half cell configuration against lithium metal, wherein the hysteresis area is measured as the area of a de-lithiation profile (V versus capacity in Coulombs per gram (Cg^-1)) minus the area of a lithiation profile, wherein the electrode is a copper foil coated with hardwood lignin-derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M lithium hexafluorophosphate (LiPFe) dissolved in a 1 :1 :1 (v/v) mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate.

[0053] The present disclosure provides coated hardwood lignin-derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a total reversible lithiation sloping capacity of greater than or equal to 310 mAh per gram (mAhg’¹), a reversible lithiation plateau capacity of greater than or equal to 50 mAhg’¹, and a hysteresis area less than or equal to 162 J per gram when tested in a half cell configuration against lithium metal, wherein the lithiation sloping capacity is defined as the reversible capacity obtained under constant current conditions at 30 mAhg^-1 and the lithiation plateau capacity is defined as the reversible capacity obtained under constant voltage conditions greater than 0 and less than 0.1 mV versus Li/Li⁺, wherein the electrode for measurement is a copper foil coated with hardwood lignin-derived hard carbon particles coated with ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M lithium hexafluorophosphate (LiPFe) dissolved in a 1 :1 :1 (v/v) mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate.

[0054] The present disclosure provides coated hardwood lignin-derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a total reversible lithiation sloping capacity of greater than or equal to 240 mAh per gram (mAhg^-1), a reversible lithiation plateau capacity of greater than or equal to 50 mAhg’¹, and a hysteresis area less than or equal to 113 J per gram when tested in a half cell configuration against lithium metal, wherein the lithiation sloping capacity is defined as the reversible capacity obtained under constant current conditions at 30 mA per gram and the lithiation plateau capacity is defined as the reversible capacity obtained under constant voltage conditions greater than 0 and less than 0.1 mV versus Li/Li⁺, wherein the electrode for measurement is a copper foil coated with hardwood lignin-derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M lithium hexafluorophosphate (LiPFe) dissolved in a 1 :1 :1 (v/v) mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate.

[0055] The present disclosure provides coated hardwood lignin-derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a reversible lithiation capacity greater than or equal to twice the reversible capacity of a graphite comparison electrode when measured at a current density of 300 mAg’¹ when tested in a half cell configuration against lithium metal, wherein the electrode for measurement is a copper foil coated with hardwood lignin-derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M lithium hexafluorophosphate (LiPFe) dissolved in a 1 :1 :1 (v/v) mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate, and the graphite comparison electrode does not comprise coated hardwood lignin-derived hard carbon particles. Thus, coated hardwood lignin-derived hard carbon particles as disclosed herein may have better capacity retention at higher charging currents, as compared to electrodes comprise graphite. This parameter indicates that coated electrodes comprising the hardwood lignin-derived hard carbon particles as disclosed herein may be faster charging than electrodes comprising graphite.

[0056] The present disclosure provides coated hardwood lignin-derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a first-cycle coulombic efficiency of greater than or equal to 85% when tested in a half cell configuration against lithium metal, wherein the electrode for measurement is a copper foil coated with hardwood lignin-derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M lithium hexafluorophosphate (LiPFe) dissolved in a 1 :1 :1 (v/v) mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate.

[0057] The present disclosure provides coated hardwood lignin-derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a first-cycle coulombic efficiency of greater than or equal to 82% and a reversible sodiation capacity of greater than or equal to 280 mAhg- ¹ when tested in a half cell configuration against sodium metal with a constant currentconstant voltage (CC-CV) cycling protocol consisting of a constant current portion with current density of 30 mAg^-1, applied until the voltage drops to 0.01 V versus Na/Na⁺ and followed by a constant voltage portion applied until the current density drops to 6 mAg^-1, wherein the electrode for measurement is a copper foil coated with hardwood lignin- derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M sodium perchlorate (NaCICM) dissolved in a 1 :1 (v/v) mixture of ethylene carbonate and diethyl carbonate with the addition of 2% fluoroethylene carbonate as an electrolyte additive.

[0058] The present disclosure provides coated hardwood lignin-derived hard carbon particles for use in an electrode, wherein the electrode comprising the coated hardwood lignin-derived hard carbon particles has a first-cycle coulombic efficiency of greater than or equal to 82%, a reversible sloping sodiation capacity of greater than or equal to 76 mAhg’¹, and a reversible plateau sodiation capacity of greater than or equal to 204 mAhg- ¹, when tested in a half cell configuration against sodium metal with a constant currentconstant voltage (CC-CV) cycling protocol consisting of a constant current portion with current density of 30 mAg^-1, applied until the voltage drops to 0.01 V versus Na/Na⁺ and followed by a constant voltage portion applied until the current density drops to 6 mAg’¹, with sloping capacity defined as corresponding to sodiation occurring above 0.1 V versus Na/Na⁺, plateau capacity defined as corresponding to sodiation occurring above 0 V and less than 0.1 V versus Na/Na⁺, and wherein the electrode for measurement is a copper foil coated with hardwood lignin-derived hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of ethylene, polyvinylidene difluoride as binder and C65 conductive carbon black in a ratio of 90:5:5 by weight, and wherein an electrolyte solution of the half cell is 1 M sodium perchlorate (NaCIO4) dissolved in a 1 :1 (v/v) mixture of ethylene carbonate and diethyl carbonate with the addition of 2% fluoroethylene carbonate as an electrolyte additive. [0059] The coated hardwood lignin-derived hard carbon particles as disclosed herein may be prepared through a method comprising thermal pretreatment, oxidative stabilization, pyrolysis, carbonization, and coating treatment (such as, for example, ethylene treatment). These steps provide coated hardwood lignin-derived hard carbon particles that are less like to fuse together. As shown in Figure 1 , electrodes coated with hardwood lignin-derived hard carbon particles according to an embodiment of the disclosure have a significantly smaller first cycle irreversible capacity as compared to an electrode coated with hardwood lignin-derived hard carbon particles not coated with pyrolytic carbon derived from thermal decomposition of a hydrocarbon. In this Figure, irreversible capacity is the difference between the lithiation capacity and the de-lithiation capacity measured at the first cycle.

[0060] The thermal pretreatment step includes extrusion or baking of the hardwood lignin under an inert atmosphere or vacuum at temperatures of about 300°C to about 400°C within a time of between about 10 seconds and about 2 hours to form a pretreated lignin.

[0061] The second step is oxidative stabilization which includes baking the pretreated lignin in air at a temperature between about 200°C and about 275°C within a time of between about 10 seconds and about 3 hours to form a stabilized lignin.

[0062] Oxidative stabilization is followed by pyrolysis. Pyrolysis involves heating the stabilized lignin in an inert atmosphere at a temperature between about 600°C and about 700°C within a time of about 0.1 hours to about 8.5 hours to form a pyrolysed lignin.

[0063] The pyrolysed lignin is then subject to carbonization by heating the pyrolysed lignin in an inert atmosphere at a temperature between about 1000°C and about 1600°C within a time of about 0.1 hours and about 36 hours to form hard carbon particles.

[0064] The hard carbon particles are then coated. For example, and as described above, the particles may be coated with pyrolytic carbon derived from thermal decomposition of ethylene or another hydrocarbon. For a hydrocarbon or ethylene treatment, also referred to as hydrocarbon treatment or ethylene treatment herein, the hard carbon particles are heated in a mixed atmosphere of an inert gas and the hydrocarbon at a temperature between about 800°C and about 1000°C within a time of between about 0.1 hours and about 6 hours to formed the coated hardwood lignin-derived hard carbon particles. In various embodiments, the inert gas is argon. The inert gas may also be nitrogen.

[0065] In various embodiments, the method may further comprise a size reduction step of the hard carbon particles prior to the coating treatment. The size reduction may be done after thermal treatment, after pyrolysis or after carbonization. Alternatively or in addition, the hard carbon particles may be classified to obtain a particle size distribution between about 1 micron or about 40 microns, or any range therebetween. The classification step may be done before or after the coating treatment.

[0066] In various embodiments, the method may further comprise one or more purification steps prior to the hydrocarbon treatment step. For example, the hardwood lignin may be purified prior to the thermal pretreatment step, the pretreated lignin may be purified prior to the oxidative stabilization step, the stabilized lignin may be purified prior to the pyrolysis step, the pyrolysed lignin may be purified prior to the carbonization step, the hard carbon particles may be purified prior to the hydrocarbon treatment, or any combination of these purification steps. Purification may be accomplished by contact the material with water or other organic solvents, alkali or acidic reagents, through high temperature treatment, or through any combination of alkali, acid and high temperature treatments.

[0067] For example, the method may further comprise a washing step to reduce inorganic impurities in the particles. The particles may be washed with an aqueous acid such as, for example, hydrochloric acid, hydrofluoric acid, sulfuric acid or nitric acid.

[0068] Following production of the coated hardwood lignin-derived hard carbon particles, these may be combined with the binder and/or the conductivity additive. The solids are then mixed with a solvent, such as N-methyl-pyrrolidone (NMP), to form an electrode slurry. In various embodiments, the binder is dissolved in the solvent and the coated hardwood lignin-derived hard carbon particles and the conductivity additive are evenly disbursed in the slurry. The slurry is coated on the current collector and the solvent is then evaporated at elevated temperature.

EXAMPLES [0069] The following Examples demonstrate characteristics of selected embodiments, illustrating for example the high reversible capacity, high first-cycle coloumbic efficiency, high capacity retention at high charging current and/or low charge-discharge voltage hysteresis of lignin-based hard carbon battery anode active materials as described herein. Selected examples are illustrative of advantages that may be obtained compared to alternative methods, and these advantages are accordingly illustrative of particular embodiments and not necessarily indicative of the characteristics of all aspects of the invention.

[0070] As used herein, the term “about” refers to an approximately +/-10% variation from a given value. It is to be understood that such a variation is always included in any given value provided herein, whether or not it is specifically referred to.

Example 1 : Preparation of hardwood lignin-derived hard carbon particles

[0071] Hardwood lignin-derived hard carbon particles were prepared through a process including the steps of thermal pre-treatment, oxidative stabilization, pyrolysis, and carbonization.

[0072] For thermal pre-treatment, a sample of lignin powder (25 g) was heated in an aluminum pan in a sealed quartz tube (4 inch outer diameter and 40 inch length) from which air was removed by vacuum and backfilled with ultra-high purity nitrogen. Under a flow of nitrogen gas (1 L/min) at approximately 1 atm of pressure, the sample was heated in a horizontal tube furnace from room temperature at about 12°C/min up to about 20,000°C/min, held at about 315°C for about 5 minutes, and then allowed to cool to below about 100°C under nitrogen. For example, the heating rate may be between about 12°C/min up to about 315°C/min. The sample was removed from the aluminum pan and ground into a powder with a mortar and pestle. Alternatively, a similar result can be achieved by feeding the lignin powder into an extruder under an oxygen-limited environment with multiple heating zones including at least one high temperature zone heated to a temperature of about 335°C to about 375°C and a specialized screw design including conveying and mixing elements. For example, the at least one high temperature zone may be heated to a temperature of about 365°C to about 375°C. Some oxygen will be present when using this approach. The total residence time varied depending on the extruder operating parameters but can be shortened to less than about 3 minutes. The result was a material which, when ground into a powder, can undergo subsequent processing in a relatively shorter period of time and also maintains its powder morphology without melting or fusing of particles. In this example, the hardwood lignin was a hardwood Kraft lignin.

[0073] After the foregoing thermal pre-treatment in an inert or oxygen-limited environment, the lignin powder was oxidatively stabilized by spreading it out onto a metal pan and heating at a rate of about 5°C/m inute in an oven to a temperature of about 225°C and about 275°C, and holding it at this temperature for a soak time of about 5 to about 60 minutes. For example, the temperature of the oven may be about 250°C. The result was a stabilized powder material that can undergo subsequent pyrolysis without melting or inter-particle fusion.

[0074] The next step in preparation of the hardwood lignin-derived hard carbon particles was pyrolysis. The stabilized lignin material was loaded into a tube furnace with a quartz tube (4 inch outer diameter and 40 inch length) in an alumina or quartz crucible, air was removed by vacuum and replaced by an inert gas such as nitrogen (as detailed above), and the material was pyrolyzed by heating the furnace to a temperature of about 600°C to about 700°C under a flow of inert gas (0.2 L/min) in the absence of oxygen, holding the temperature for a soak time of about 10 minutes to about 60 minutes, and cooling to room temperature under inert gas. The result was a carbon-rich char powder. [0075] For carbonization, the char powder was similarly heated in the tube furnace under an inert atmosphere using a refractory ceramic tube (mullite or alumina), from room temperature to about 1000°C to about 1500°C, held for a soak time of about 5 minutes to about 60 minutes, and cooled to room temperature under an inert atmosphere. The result was the hardwood lignin-derived hard carbon particles as a powder material.

Example 2 - Preparation of coated hardwood lignin-derived hard carbon particles

[0076] In this Example, the hardwood lignin-derived hard carbon particles were subject to an ethylene treatment for coating. The uncoated hard carbon powder was heated in a furnace designed for chemical vapor deposition (CVD). First, the reactor was heated to a temperature of about 800°C to about 1000°C in argon, then once the reactor reached the target temperature, ethylene gas was introduced with an appropriate flow rate for an appropriate amount of time such that a thin layer of soft carbon was deposited onto the surface of the hard carbon particles. The material was then cooled under an inert atmosphere to room temperature. The result was a coated hard carbon suitable for use as a negative electrode active material in lithium or sodium ion batteries.

Example 3 - Preparation of lithium half cells

[0077] The coated hard carbon particles were mixed with polyvinylidene difluoride (PVDF) as binder and C65 conductive carbon black as conductivity enhancer in a ratio of 90:5:5 (hard carbon : PVDF : carbon black) by weight and the solids were mixed with N- methyl-pyrrolidone (NMP) solvent (4.44 g solids in 9.22 g of NMP) and mixed to form an electrode slurry such that the PVDF was dissolved and the hard carbon and carbon black were evenly dispersed. The slurry was coated onto a copper foil and the solvent was evaporated at elevated temperature. The mass of hard carbon per square centimeter of electrode area was about 5 mg/cm² to about 6 mg/cm², and is specified where applicable. CR 2032 lithium half cells were prepared using lithium metal as a counter/reference electrode, Whatman 1820 glass fibre as a separator, and an electrolyte solution consisting of 1 M lithium hexafluorophosphate (LiPFe) dissolved in a 1 :1 :1 (v/v) mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate.

Example 4 - Lithium half cell cycling

[0078] A 25-cycle protocol was applied to evaluate the first cycle coulombic efficiency (FCE) and the reversible lithiation capacity of the lithium half cells prepared in Example 3. Cycling was performed at a temperature of 25°C in a potential range between 2.5 V and 0.01 V versus Li/Li⁺. FCE is defined as the value of the first de-lithiation capacity divided by the first lithiation capacity multiplied by 100, and reversible capacity is defined at specified current density after the first 5 cycles. The current densities were 30 mA/g of active material for cycles 1 -5, 60 mA/g for cycles 6-10, 150 mA/g for cycles 11 -15, 300 mA/g for cycles 16-20, and 30 mA/g for cycles 21 -25. In cycles 1 -5 and cycles 21 -25, a combination of galvanostatic (constant current) and potentiostatic (constant voltage) modes were applied to evaluate the full lithiation capacity of the hard carbon materials (Figure 2).

[0079] The galvanostatic portion of the lithiation was conducted at 30 mA/g until the voltage reached a value of 0.01 V vs Li/Li⁺, and then the potentiostatic portion of the lithiation proceeded until the current dropped to a value of 6 mA/g. The de-lithiation was conducted galvanostatically at 30 mA/g. In cycles 6-20, lithiation was conducted in galvanostatic mode at 3 different current densities (60, 150, 300 mA/g) and de-lithiation was conducted galvanostatically at 30 mA/g. Hysteresis was quantified by subtracting the area under the lithiation profile from the area under the de-lithiation profile (potential vs capacity). When potential is expressed in volts (Volt = Joule/Coulomb, V = J/C), and capacity is expressed in Coulombs per gram (1 mAh = 3.6 C), the area under the voltage profile has the units of J/g (Figure 3).

Example 5 - Preparation of sodium half cells and sodium half cell cycling

[0080] For preparation of sodium half cells, the same procedure was used as described in Example 3 except sodium metal was used in place of lithium and the electrolyte was a mixture of 1 M sodium perchlorate (NaCICM) dissolved in a 1 :1 (v/v) mixture of ethylene carbonate and diethyl carbonate with the addition of 2% fluoroethylene carbonate (FEC) as an electrolyte additive. The sodium cells were cycled for at least 25 cycles in a manner similar to the lithium half cells at 25°C in a potential range of 2.5 - 0.01 V vs Na/Na⁺. For all cycles, a combination of galvanostatic (constant current) and potentiostatic (constant voltage) modes was applied to evaluate the full sodiation capacity of the hard carbon materials (Figure 4). The galvanostatic portion of the sodiation was conducted at 30 mA/g until the voltage reached a value of 0.01 V vs Na/Na⁺, and then the potentiostatic portion of the sodiation proceeded until the current dropped to a value of 6 mA/g. The de-sodiation was conducted galvanostatically at 30 mA/g. Figure 5 shows the voltage profile of the 10th cycle of the Na/hard carbon half cell expressed in V vs capacity in mAh/g.

[0081] Although various embodiments of the invention are disclosed herein, many adaptations and modifications may be made within the scope of the invention in accordance with the common general knowledge of those skilled in this art. Such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way. Numeric ranges are inclusive of the numbers defining the range. The word "comprising" is used herein as an open-ended term, substantially equivalent to the phrase "including, but not limited to", and the word "comprises" has a corresponding meaning. As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a thing" includes more than one such thing. Citation of references herein is not an admission that such references are prior art to the present invention. Any priority document(s) and all publications, including but not limited to patents and patent applications, cited in this specification are incorporated herein by reference as if each individual publication were specifically and individually indicated to be incorporated by reference herein and as though fully set forth herein. The invention includes all embodiments and variations substantially as hereinbefore described and with reference to the examples and drawings.

Claims

1 . A method for preparing coated hardwood lignin-derived hard carbon particles from a hardwood lignin, the method comprising the following steps: thermal pretreatment comprising extrusion or baking of the hardwood lignin under inert atmosphere or vacuum at temperatures of 300°C to 400°C within a time of between 10 seconds and 2 hours to form a pretreated lignin; oxidative stabilization comprising baking the pretreated lignin in air at a temperature between 200°C and 250°C within a time of between 10 seconds and 3 hours to form a stabilized lignin; pyrolysis comprising heating the stabilized lignin in an inert atmosphere at a temperature between 600°C and 700°C within a time of 0.1 hours to 8.5 hours to form a pyrolysed lignin; carbonization comprising heating the pyrolysed lignin in an inert atmosphere at a temperature between 1000°C and 1600°C within a time of 0.1 and 36 hours to form hard carbon particles; and hydrocarbon treatment comprising heating the hard carbon particles in a mixed atmosphere of argon and a hydrocarbon at a temperature between 800°C and 1000°C within a time of 0.1 hours and 6 hours to form the coated hardwood lignin-derived hard carbon particles, the hard carbon particles coated with pyrolytic carbon derived from thermal decomposition of the hydrocarbon.

2. The method of claim 1 , wherein the hardwood lignin derivative is a hardwood Kraft lignin.

3. The method of claim 1 or 2, wherein the hydrocarbon is ethylene.

4. The method of claim 1 , 2 or 3, further comprising: (a) size reduction of the hard carbon particles prior to the hydrocarbon treatment, and/or (b) classification of the hard carbon particles before or after the hydrocarbon treatment to a particle size distribution between about 1 micron and about 40 microns.

5. The method of claim 4, wherein the size reduction is done after thermal treatment, after pyrolysis or after carbonization.

6. The method of claim 4, wherein the classification is done before or after the hydrocarbon treatment.

7. The method of any one of claims 1 to 6, further comprising washing the hard carbon particles with an aqueous acid prior to the hydrocarbon treatment.

8. The method of claim 7, wherein the aqueous acid is hydrochloric acid, hydrofluoric acid, sulfuric acid, or nitric acid.

9. The method of any one of claims 1 to 6, further comprising one or more purification steps prior to the hydrocarbon treatment.

10. The method of claim 9, wherein the hardwood lignin is purified prior to the thermal pretreatment step.

11 . The method of claim 9 or 10, wherein the pretreated lignin is purified prior to the oxidative stabilization step.

12. The method of claim 9, 10 or 11 , wherein the stabilized lignin is purified prior to the pyrolysis step.

13. The method of any one of claims 9 to 12, wherein the pyrolysed lignin is purified prior to the carbonization step.

14. The method of any one of claims 9 to 13, wherein the hard carbon particles are purified prior to the hydrocarbon treatment.

15. Coated hardwood lignin-derived hard carbon particles produced according to the method as defined in any one of claims 1 to 14.

16. The coated hardwood lignin-derived hard carbon particles of claim 15, for use as an electrode active layer for an electrode.

17. The coated hardwood lignin-derived hard carbon particles of claim 15, for use as the electrode active layer for an anode.

18. The coated hardwood lignin-derived hard carbon particles of claim 15, for use as an electrode active layer for an anode in a lithium ion battery or in a sodium ion battery.

19. An electrode comprising a current collector coated with hardwood lignin-derived hard carbon particles as defined in any one of claims 15-18, a binder and a conductivity additive, wherein a ratio of the hardwood lignin-derived hard carbon particles : the binder : the conductivity additive is between 80:10:10 and 99:1 :1.

20. The electrode of claim 19, wherein the binder is polyvinylidene difluoride, and/or the conductivity additive is C65 conductive carbon black.