WO2025097059A1 - All-solid-state lithium secondary batteries and methods of preparing the same - Google Patents

Abstract

Embodiments pertain to an interlayer suitable for use in solid-state batteries. Such interlayers generally include: (1) a plurality of carbon nanomaterials; and (2) a plurality of magnesium (Mg) nanoparticles uniformly dispersed on the carbon nanomaterials. After lithiation, the interlayers also include a percolating network operational for regulating ion flux through the interlayer due to the volume expansion of Mg nanoparticles. Additional embodiments pertain to solid-state batteries that include such interlayers, methods of forming such interlayers, and methods of forming solid-state batteries that include the interlayers.

Description

TITLE

ALL-SOLID-STATE LITHIUM SECONDARY BATTERIES AND METHODS OF PREPARING THE SAME

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63/546,985, filed on November 2, 2023. The entirety of the aforementioned application is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] This invention was made with government support under DE-AC05-76RL01830, awarded by the U.S. Department of Energy. The government has certain rights in the invention.

BACKGROUND

[0003] A need exists for the development of more effective interlayers for solid-state energy storage devices. Numerous embodiments of the present disclosure address this need.

SUMMARY

[0004] In some embodiments, the present disclosure pertains to an interlayer for a solid-state battery. In some embodiments, the interlayer includes a plurality of carbon nanomaterials and a plurality of magnesium (Mg) particles uniformly dispersed on the carbon nanomaterials. In some embodiments, the Mg particles include Mg nanoparticles. In some embodiments, the Mg nanoparticles include average diameters below 1 pm.

[0005] Additional embodiments of the present disclosure pertain to solid-state batteries that include an interlayer of the present disclosure. In some embodiments, the solid-state batteries of the present disclosure may include: a cathode; a solid electrolyte; a current collector; and an interlayer of the present disclosure positioned between the solid electrolyte and the current collector. In some embodiments, the interlayer is in contact with the solid electrolyte. In some embodiments, the solid- state battery also includes an anode positioned between the current collector and the interlayer.

[0006] Further embodiments of the present disclosure pertain to anode-free solid-state batteries that include the interlayers of the present disclosure. In some embodiments, the anode-free solid-state lithium battery includes: a cathode; an electrolyte in contact with the cathode; a current collector; and an interlayer of the present disclosure positioned between the current collector and the solid electrolyte. [0007] Additional embodiments of the present disclosure pertain to methods of forming an interlayer with a percolating network capable of regulating ion flux therethrough. In some embodiments, the methods of the present disclosure include associating a plurality of Mg nanoparticles with a plurality of carbon nanomaterials. In some embodiments, the carbon nanomaterials are in the form of a substrate and include nanometer-sized dimensions. In some embodiments, the Mg nanoparticles become uniformly integrated in the carbon nanomaterial substrate. In some embodiments, the association results in the formation of a uniform Mg nanoparticle-carbon nanomaterial substrate composite.

[0008] Additional embodiments of the present disclosure pertain to methods of forming a solid-state battery. In some embodiments, such methods include: (1) attaching an interlayer of the present disclosure to a solid electrolyte; and (2) attaching an anode to the interlayer. In some embodiments, the solid-state battery formation methods of the present disclosure include steps of (1) attaching an interlayer to a surface of an anode to form an anode-interlayer assembly; and (2) attaching the anodeinterlayer assembly to a solid electrolyte-cathode assembly to form an anode-interlayer-solid- electrolyte-cathode assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1A provides an illustration of a solid-state battery in accordance with various embodiments of the present disclosure.

[0010] FIG. IB provides an illustration of an anode-free solid-state battery in accordance with various embodiments of the present disclosure.

[0011] FIGS. 1C-1D provide illustrations of an all-solid-state secondary lithium battery with an interlayer. The battery can be fabricated in two designs: A Li-anode design (FIG. 1C) or an “anode- free” design (FIG. ID). In the “anode-free” design, a Li anode forms in situ during the initial charge. Cell components are labeled in numbers. 401: cathode active material; 402: solid electrolyte; 403: interlayer; 404: Li metal (i.e., anode); and 405: current collector.

[0012] FIGS. 2A-2B show phase diagrams of Li-Mg (FIG. 2A) and Li-Ag (FIG. 2B) systems (high Li content region).

[0013] FIGS. 3A-3C show cycling performance of an all- solid- state lithium cell with a Mg-C interlayer. FIG. 3A shows a cross-section scanning electron microscopy (SEM) image of Mg-C interlayer on Ni substrate before cycling, and Mg-C interlayer in solid-state battery after cycling. FIGS. 3B-3C show the rate capability (FIG. 3B) and longevity test (FIG. 3C) of NMC | LiePSsCl | Mg-C | Li cell at 30 °C. The areal loading is 2.8 mAh cm ² and the cell was cycled at 1 C (2.8 mA cm ²) for the longevity test.

[0014] FIGS. 4A-4C show SEM images, Mg mapping and C mapping of pristine Mg-C interlayers fabricated by electrochemical deposition of Mg. FIG. 4D shows a first two cycle electrochemical performance of anode-free solid-state batteries with a Mg-C interlayer. FIG. 4E shows the morphology of a Mg-C interlayer after plating Li (3 mAh/cm²). Li was transported through and deposited beneath Mg-C in anode-free solid-state batteries. FIG. 4F shows a first two cycle electrochemical performance of anode-free solid-state batteries with a C interlayer. FIG. 4G shows a morphology of a C interlayer after plating Li (3 mAh/cm²). Li was deposited between SE and C in anode-free solid-state batteries. Cell components are labeled in numbers. 401: Li metal; 402: solid electrolyte; 403: Mg-C interlayer; 404: plated Li metal; 405: interlayer.

[0015] FIG. 5 illustrates material screening based on periodic table and a phase diagram. Elements are colored based on their solubility in Li 0 phase (bcc). Elements that form intermetallic ionic compounds are patterned.

[0016] FIG.6A illustrates the difference in the lithiation behavior of Ag-C and Mg-C in the interlayer. Components in the illustration are labeled in numbers. 601: solid electrolyte; 602: carbon; 603: Ag particle; 604: pure Li; 605: Li-Ag alloy; 606: Mg particle; 607: Li-Mg alloy. FIGS. 6B-6C show the voltage-capacity profile and differential capacity profile of Ag-C and Mg-C interlayers during lithiation.

DETAILED DESCRIPTION

[0017] It is to be understood that both the foregoing general description and the following detailed description are illustrative and explanatory, and are not restrictive of the subject matter, as claimed. In this application, the use of the singular includes the plural, the word “a” or “an” means “at least one”, and the use of “or” means “and/or”, unless specifically stated otherwise. Furthermore, the use of the term “including”, as well as other forms, such as “includes” and “included”, is not limiting. Also, terms such as “element” or “component” encompass both elements or components comprising one unit and elements or components that include more than one unit unless specifically stated otherwise.

[0018] The section headings used herein are for organizational purposes and are not to be construed as limiting the subject matter described. All documents, or portions of documents, cited in this application, including, but not limited to, patents, patent applications, articles, books, and treatises, are hereby expressly incorporated herein by reference in their entirety for any purpose. In the event that one or more of the incorporated literature and similar materials defines a term in a manner that contradicts the definition of that term in this application, this application controls.

[0019] All-solid-state lithium metal batteries are projected to offer one of the highest specific energy among rechargeable batteries. To increase cell-level energy density, a lithium metal anode (3860 mAh g^-1 and -3.04 V vs. standard hydrogen potential) outperforms a conventional graphite anode. Metalelectrolyte contact is a great challenge in all-solid-state batteries. Intrinsic surface roughness of both the lithium metal and the electrolyte results in poor interfacial contact, which acts as a precursor for lithium dendritic growth. The volumetric change of the lithium metal anode during stripping produces voids, which further deteriorates the metal-electrolyte contact.

[0020] An interlayer strategy has been reported by other groups between solid electrolyte and lithium metal, or between solid electrolyte and current collector, to buffer mechanical strain, promote better interfacial contact, alleviate chemical instability, improve stripping/plating homogeneity, and therefore suppress lithium dendrite formation and propagation. For instance, prior studies have demonstrated the use of mixed ionic-and-electronic conductor (MIEC) interlayer with silver-carbon (silver particle size 50-60 nm), which enabled high energy (>900 Wh L ¹ ), high current density (3.4 mA cm ²) and long cycle life (>900 cycles) for all- solid- state batteries at 60 °C.

[0021] For electric vehicle (EV) applications, room- temperature operation (charge and discharge) is desirable. However, prior studies showed high-current-density charging only at elevated temperature (60 °C). Moreover, existing technologies utilize noble metal (Ag) nanoparticles mixed with carbon and binder to produce interlayers. A typical Ag-C composite interlayer contains silver at 61-123 mg Ah^-1, corresponding to 17-33 grams of silver per kWh in NMC-based full cells, accounting for 10- 20% of a battery cost. Ag costs $900k per ton, while other metals cost $2.6 per ton. Moreover, low abundance of Ag in the Earth’s crust (10 ⁶ that of Mg) hinders Ag-containing interlayers to satisfy the gigawatt-hour market. [0022] As such, a need exists for the development of more effective interlayers for solid-state energy storage devices. Numerous embodiments of the present disclosure address this need.

[0023] Interlayers

[0024] In some embodiments, the present disclosure pertains to an interlayer. In some embodiments, the interlayer may be suitable for use in a solid-state battery. In some embodiments, the interlayer includes a plurality of carbon nanomaterials and a plurality of magnesium (Mg) particles uniformly dispersed on the carbon nanomaterials. As set forth in more detail herein, the interlayers of the present disclosure can have numerous embodiments and variations.

[0025] Carbon nanomaterials

[0026] The interlayers of the present disclosure can include numerous carbon nanomaterials. For instance, in some embodiments, the carbon nanomaterials are in the form of a substrate. In some embodiments, the carbon nanomaterials include, without limitation, carbon powder, carbon nanoparticles, amorphous carbon, porous carbon, carbon black, Ketjen Black, carbon nanotubes, vapor-grown carbon nanofibers, oxidized carbons, or combinations thereof.

[0027] In some embodiments, the carbon nanomaterials include oxidized carbon. In some embodiments, the oxidized carbon includes oxygen-based surface groups. In some embodiments, the oxygen-based surface groups include, without limitation, hydroxyl surface groups, oxide surface groups, or combinations thereof.

[0028] The interlayers of the present disclosure can include various amounts of carbon nanomaterials. For instance, in some embodiments, the interlayer includes from about 10 wt% to about 90 wt% of the carbon nanomaterials. In some embodiments, the interlayer includes from about 10 wt% to about 50 wt% of the carbon nano materials. In some embodiments, the interlayer includes from about 10 wt% to about 25 wt% of the carbon nanomaterials.

[0029] The carbon nanomaterials of the present disclosure can include various dimensions. For instance, in some embodiments, the carbon nanomaterials include nanometer- sized dimensions. In some embodiments, the nanometer- sized dimensions range from about 1 nm to about 100 nm.

[0030] Mg particles

[0031] The interlayers of the present disclosure can include various Mg particles. For instance, in some embodiments, the Mg particles are operable to undergo a peritectic reaction with lithium (Li). In some embodiments, the metals are soluble in a Li solid solution phase. [0032] In some embodiments, the diffusivity of metals of the Mg particles in a lithium (Li) solid solution phase is smaller than Li self-diffusivity. In some embodiments, the Mg particles expand upon contact with Li metal. In some embodiments, the Mg particles expand upon contact with lithium (Li) metal and become interconnected within the interlayer due to volume expansion to form a percolating network. In some embodiments, the percolating network is capable of selectively conducting flow of ions while restricting flow of electrons.

[0033] The Mg particles of the present disclosure can include various sizes. For instance, in some embodiments, the Mg particles include average diameters ranging from about 1 nm to about 1000 nm. In some embodiments, the Mg particles include average diameters ranging from about 1 nm to about 100 nm. In some embodiments, the Mg particles include average diameters of less than about 100 nm. In some embodiments, the Mg particles include average diameters of less than about 1000 nm.

[0034] In some embodiments, the Mg particles include Mg nanoparticles. In some embodiments, the Mg nanoparticles include average diameters below 1 pm. In some embodiments, the magnesium: carbon nanomaterial mass ratio ranges between 1:30 to 1:8.

[0035] Binders

[0036] In some embodiments, the interlayers of the present disclosure also include a binder. In some embodiments, the binder includes a polymer. In some embodiments, the polymer includes poly vinylidene fluoride.

[0037] In some embodiments, the interlayer is positioned between an anode and a solid electrolyte. In some embodiments, the interlayer is positioned between a current collector and a solid electrolyte. In some embodiments, the interlayer includes a mixed ionic-and-electronic conductor (MIEC) interlayer. In some embodiments, the interlayer forms a peritectic alloy with lithium metal.

[0038] Solid-state batteries

[0039] Additional embodiments of the present disclosure pertain to solid-state batteries that include an interlayer of the present disclosure. In some embodiments, the solid-state battery includes, without limitation, an all- solid- state battery (ASSB), an all- solid- state lithium metal battery (ASSLMBs), allsolid-state lithium secondary battery, an anode-free solid-state battery, or combinations thereof.

[0040] In some embodiments, the solid-state batteries of the present disclosure also include an anode and a solid electrolyte. In some embodiments, the interlayer is positioned between the anode and the solid electrolyte. In some embodiments, the anode includes a layer of lithium metal. In some embodiments, the solid electrolyte includes an oxide-based electrolyte.

[0041] In some embodiments, the solid-state batteries of the present disclosure also include a current collector and a solid electrolyte. In some embodiments, the interlayer is positioned between the current collector and the solid electrolyte.

[0042] The interlayers of the present disclosure may have various advantageous effects in the solid- state batteries of the present disclosure. For instance, in some embodiments, the interlayer is operational to optimize the interface between the anode and the solid electrolyte, thereby minimizing the formation of dendrites.

[0043] In some embodiments, the solid-state batteries of the present disclosure also include a cathode. In some embodiments, the cathode includes a transition metal oxide cathode. In some embodiments, the cathode includes a cathode active material layer. In some embodiments, the cathode is a lithium- ion cathode.

[0044] In some embodiments, the solid-state batteries of the present disclosure may be illustrated as solid-state battery 10 in FIG. 1A. In some embodiments, solid-state battery 10 includes: a cathode 12; a solid electrolyte 14; a current collector 18; and an interlayer 15 positioned between the solid electrolyte 14 and the current collector 18. In some embodiments, the interlayer 15 is in contact with the solid electrolyte 14. In some embodiments, interlayer 15 includes an interlayer of the present disclosure. For instance, in some embodiments, interlayer 15 includes: a plurality of carbon nanomaterials 16, and a plurality of Mg nanoparticles 17 uniformly dispersed on the carbon nanomaterials 16.

[0045] In some embodiments, the Mg nanoparticles 17 expand upon lithiation. In some embodiments, the lithiated interlayer 15 includes a percolating network operational for regulating ion flux through interlayer 15 such that the battery is capable of high rate cycling greater than 2.5 mA cm ² at areal capacities greater than 2 mAh cm ² under ambient temperatures of about 30 °C or less.

[0046] In some embodiments, solid-state battery 10 also includes an anode 20 positioned between current collector 18 and interlayer 15. In some embodiments, anode 20 includes a lithium metal. In some embodiments, metal elements in the interlayer inter-diffuses with the lithium metal. In some embodiments, the self-diffusion coefficient of lithium is smaller than the diffusion coefficient of the metal elements in the lithium. In some embodiments, the interdiffusion facilitates the volume expansion of the Mg nanoparticles and subsequent interconnection of the Mg nanoparticles within the interlayer.

[0047] In some embodiments, Mg nanoparticles 17 of interlayer 15 are operable to inter-diffuse with the lithium metal to form an alloy. In some embodiments, metal elements in interlayer 15 inter-diffuse with the lithium metal at a comparable rate to form an alloy. In some embodiments, the diffusion coefficient of the lithium in the metal elements is of the same order of magnitude as the diffusion coefficient of the metal elements in the lithium. In some embodiments, the interdiffusion facilitates the formation of a lithium-conducting percolating network.

[0048] In some embodiments, the solid-state batteries of the present disclosure include anode-free solid-state batteries. Additional embodiments of the present disclosure pertain to anode-free solid- state batteries that include the interlayers of the present disclosure. Anode-free solid-state batteries of the present disclosure may be illustrated as anode-free solid-state battery 30 in FIG. IB. In some embodiments, anode-free solid-state lithium battery 30 includes: a cathode 32; an electrolyte 34 in contact with the cathode 32; a current collector 38; and an interlayer 35 positioned between the current collector 38 and the solid electrolyte 34.

[0049] In some embodiments, interlayer 35 includes an interlayer of the present disclosure. For instance, in some embodiments, interlayer 35 includes: a plurality of carbon nanomaterials 36 that are in the form of a substrate. In some embodiments, interlayer 35 also includes a plurality of Mg nanoparticles 37 uniformly dispersed throughout the carbon nanomaterials 36 to form a percolating network. In some embodiments, the percolating network is operable to regulate lithium ion flux through interlayer 35.

[0050] Methods of forming interlayers

[0051] Additional embodiments of the present disclosure pertain to methods of forming the interlayers of the present disclosure. In some embodiments, the methods of the present disclosure include mixing a carbon nanomaterial with a Mg particle precursor to form a product, where the product includes Mg particles uniformly dispersed on the carbon nano materials. In some embodiments, the methods of the present disclosure also include a step of associating the product with a binder.

[0052] In some embodiments, the methods of the present disclosure also include a step of incorporating the formed interlayer as a component of a solid-state battery. In some embodiments, the incorporation includes pressing the formed interlayer onto a surface of an anode. In some embodiments, the pressing occurs by a method that includes, without limitation, hydraulic pressing, isostatic pressing, or combinations thereof.

[0053] The methods of the present disclosure can include various mixing steps. For instance, in some embodiments, the mixing step occurs by a method that includes, without limitation, sonication, ultrasonication, mortar-and-pestle mixing, shear-force homogenization, planetary mixing, planetary milling, wet milling, agitation in solvent media, sonication in solvent media, vortex mixing, chemical precipitation, co-precipitation mixing, electrochemical deposition, thermal decomposition, or combinations thereof.

[0054] In some embodiments, the mixing includes directly depositing Mg particles on the surface of carbon nanomaterials. In some embodiments, the deposition occurs by electrochemical or chemical steps.

[0055] The methods of the present disclosure may utilize various Mg particle precursors. For instance, in some embodiments, the Mg particle precursor includes, without limitation, solvated Mg salts, Mg counter electrodes, or combinations thereof.

[0056] The methods of the present disclosure may be utilized to form various Mg particles. Suitable Mg particles were described supra and are incorporated herein by reference. For instance, in some embodiments, the Mg particles are in non- aggregated form. In some embodiments, the Mg particles include average diameters ranging from about 1 nm to about 1000 nm. In some embodiments, the Mg particles include average diameters ranging from about 1 nm to about 100 nm. In some embodiments, the Mg particles include average diameters of less than about 100 nm.

[0057] The methods of the present disclosure may utilize various carbon nanomaterials. Suitable carbon nanomaterials were described supra and are incorporated herein by reference. For instance, in some embodiments, the carbon nanomaterials include, without limitation, carbon powder, carbon nanoparticles, amorphous carbon, porous carbon, carbon black, Ketjen Black, carbon nanotubes, vapor-grown carbon nanofibers, oxidized carbons, or combinations thereof. In some embodiments, the carbon nanomaterials constitute from about 10 wt% to about 90 wt% of the interlayer.

[0058] In some embodiments, the carbon nanomaterials include oxidized carbon. In some embodiments, the methods of the present disclosure also include a step of treating the carbon nanomaterials with an acid to form oxidized carbon. In some embodiments, the treatment occurs prior to the mixing step. In some embodiments, the acid includes nitric acid. In some embodiments, the oxidized carbon includes oxygen-based surface groups. In some embodiments, the oxygen-based surface groups include, without limitation, hydroxyl surface groups, oxide surface groups, or combinations thereof.

[0059] The methods of the present disclosure may also utilize various binders. Suitable binders were also described supra and are incorporated herein by reference. For instance, in some embodiments, the binder includes a polymer. In some embodiments, the polymer includes polyvinylidene fluoride. [0060] The methods of the present disclosure may form various interlayers. Suitable interlayers were described supra and are incorporated herein by reference. For instance, in some embodiments, the interlayer forms a peritectic alloy with lithium metal. In some embodiments, the interlayer includes a mixed ionic-and-electronic conductor (MIEC) interlayer.

[0061] In some embodiments, the plurality of Mg particles of the interlayer form a percolating network. In some embodiments, the percolating network is operable to enable rapid lithium transport through the interlayer and thereby prevent dendrite formation. In some embodiments, the Mg particles of the interlayer become bonded to the surface of the interlayer carbon nano materials.

[0062] In some embodiments, the present disclosure pertains to methods of forming an interlayer with a percolating network capable of regulating ion flux therethrough. In some embodiments, the methods of the present disclosure include associating a plurality of Mg nanoparticles with a plurality of carbon nanomaterials. In some embodiments, the carbon nanomaterials are in the form of a substrate and include nanometer- sized dimensions. In some embodiments, the Mg nanoparticles become uniformly integrated in the carbon nanomaterial substrate. In some embodiments, the association results in the formation of a uniform Mg nanoparticle-carbon nanomaterial substrate composite. In some embodiments, the association step occurs by a method that includes, without limitation, chemical precipitation, electrochemical deposition, ultrasonication, thermal decomposition, or a combination thereof. In some embodiments, the Mg nanoparticles include diameters between about 5 nm to about 1000 nm.

[0063] Methods of forming solid-state batteries

[0064] Additional embodiments of the present disclosure pertain to methods of forming a solid-state battery. In some embodiments, such methods include: (1) attaching an interlayer of the present disclosure to a solid electrolyte; and (2) attaching an anode to the interlayer. In some embodiments, the solid electrolyte is attached to a cathode. In some embodiments, the solid-state battery formation methods of the present disclosure include steps of (1) attaching an interlayer to a surface of an anode to form an anode-interlayer assembly; and (2) attaching the anode-interlayer assembly to a solid electrolyte-cathode assembly to form an anode-interlayer-solid-electrolyte-cathode assembly.

[0065] In some embodiments, the interlayer includes a plurality of carbon nano materials. In some embodiments, the carbon nanomaterials are in the form of a substrate. In some embodiments, the interlayer also includes a plurality of Mg nanoparticles uniformly dispersed on the carbon nanomaterials. In some embodiments, the Mg nanoparticles form a coating on the carbon nanomaterials without aggregating. In some embodiments, the interlayer also includes a percolating network operable for regulating an ion flux therethrough.

[0066] In some embodiments, the Mg nanoparticles expand upon contact with a lithium source and become interconnected to form a percolating network operable for regulating an ion flux therethrough. [0067] In some embodiments, the anode includes a current collector. In some embodiments, the anode also includes a layer of anode metal. In some embodiments, the anode includes lithium. In some embodiments, the metal nanoparticles include Mg nanoparticles.

[0068] Additional embodiments

[0069] Reference will now be made to more specific embodiments of the present disclosure and experimental results that provide support for such embodiments. However, Applicant notes that the disclosure below is for illustrative purposes only and is not intended to limit the scope of the claimed subject matter in any way.

[0070] Example 1. Development of an all-solid-state lithium secondary battery

[0071] This Example describes an all- solid- state lithium secondary battery that includes a positive electrode, a solid electrolyte separator, a lithium metal layer and an interlayer in all- solid- state secondary batteries. The interlayer includes finely dispersed, lithium-reactive, Mg (magnesium, Mg) nanoparticles as the active component.

[0072] The interlayer is positioned between a solid electrolyte layer and Li (or Li alloy) or between a solid electrolyte layer and a current collector in an anode-free configuration. The interlayer includes Mg nanoparticles, carbon, and polymeric binders.

[0073] The interlayer is formed with a slurry coating process. The cell that includes this interlayer shows unprecedented stability over 1200 cycles without forming Li dendrites at temperatures between -20 to 30 °C. Li in the BCC -phase of a Li-Mg alloy provides large solubility without experiencing phase transition. Moreover, this interlayer eliminated the need to use noble metals. Replacing Ag with Mg drastically reduces metal weight and material cost for the interlayer.

[0074] This Example aims in part to resolve the instability of Li metal anodes in all- solid- state batteries (ASSBs). MIEC-type interlayer started to gain attention recently. A typical MIEC interlayer is composed of carbon (to provide structural support and electron conduction), metal (to assist Li transport), and binder (to enable scale up processing). It helps to protect ASSBs from electrolyte penetration by mechanically insulating Li metal anode and solid electrolyte, as well as separating the redox reaction and Li deposition/dissolution process.

[0075] FIGS. 1C-1D show the structure of an all-solid-state lithium secondary battery with an interlayer. The presence of metal nanoparticles such as Ag or Mg may help decrease the nucleation barrier of lithium, as well as to increase lithium mobility by alloying, which enabled prolonged cycling at high current density and elevated temperature (60 °C).

[0076] The experimental results demonstrate that a Mg-C interlayer with nano-dispersed Mg enables stable cycling of ASSB at high current density and ambient temperature (30 °C). The working mechanisms of Mg-C interlayer and Ag-C interlayer are different. Upon reaction with Li, Li-Mg forms peritectic with a higher melting temperature, suppressing Li diffusion within the alloy. This contrasts with Li-Ag, which forms a eutectic, reducing the metal’s melting point (T_m decrease to 145 °C), as demonstrated in the phase diagrams in FIGS. 2A-2B.

[0077] According to the hypothesized working mechanisms in existing literature, one might anticipate that the Mg-C interlayer would exhibit inferior performance compared to its Ag-C counterparts. However, unexpectedly, Applicant found that Mg-C shows competitive performance with Ag-C reported in the literature, which either required high temperature, or additional adhesive between electrolyte and interlayer to function.

[0078] FIGS. 3A-3C show the cycling performance of full cell (LiNio.saMno.iiCoo.oeChlLiePSsCllMg- C|Li), which included a Mg-C interlayer. The cell cycles at a high current density (2.8 mA cm ²) at 30 °C for more than 1200 cycles. This suggests Li transport in Mg-C interlayer does not rely on the “premelting mechanism” proposed by existing work, and the operation of the cell does not require elevated operating temperature or strong adhesion between the interlayer and solid electrolyte.

[0079] It is important to note that Mg-C interlayers prepared by different methods operate similarly. For instance, the Mg-C interlayer in FIG. 3A uses a direct mixing method, where Mg nanopowders and carbon nanopowders are directly mixed with mortar and pestle. The white shades in the “pristine” image represent the location of Mg particles. After cycling, Mg-C becomes fully lithiated, as evidenced by the identical image contrast of particles (Li-Mg alloy in Li BCC phase) within interlayer compared to Li substrate at the bottom.

[0080] Alternatively, Mg can be electrochemically deposited into porous carbon film, as shown in FIGS. 4A-4G. Mg shows uniform distribution in Mg-C film prepared by an electrochemical deposition method, as shown by uniform Mg and C mapping in FIGS. 4A-4C. A plating test on the interlayer shows Li can transport through Mg-C and deposit on the counter side of the interlayer in FIGS. 4D-4E. In contrast, an interlayer of carbon alone cannot provide sufficient Mg transport capability (FIGS. 4F-4G). Additionally, Li deposits between the solid electrolyte and interlayer, causing lower Coulombic efficiency and risk of cell short-circuiting.

[0081] Moreover, the preparation of a Mg-containing interlayer is not trivial due to Mg metal’s reactivity and ductility. Unlike Ag nanoparticles that are stable in air, Mg nanoparticles are vulnerable to oxidation and could be pyrophoric at ambient conditions.

[0082] Applicant has developed approaches to finely dispersed Mg in carbon-based interlayer films and demonstrated all- solid- state batteries with Mg-containing interlayer that cycles at high current density and shows long cycle life. As such, Li metal transports through the mixed-conducting interlayer and deposits between the interlayer and current collector.

[0083] Without being bound by theory, Applicant envisions that Mg’s large solubility in the Li metal BCC phase plays an important role in the interlayer. Applicant hypothesizes that Li⁺ ion first reduces at the interlayer-electrolyte interface. Then, atomic Li diffuses through the interlayer towards Li anode and current collector. In the proposed diffusion model, the solubility of metal in Li and its reactivity with Li is important. If the metal is insoluble in Li, the interlayer becomes less lithiophilic, and the reduced Li tends to nucleate and deposit at the interlayer-electrolyte interface. If the metal forms ionic or intermetallic compounds with Li, it becomes too stable and traps Li within the interlayer. An ideal candidate of metal should be soluble in Li and does not form intermetallic or ionic compounds with Li.

[0084] As illustrated in FIG. 5, Applicant screened the solubility limit of various elements in Li (BCC phase) and whether they react with Li. Only Ag and Mg showed solubility in Li (BCC phase) to some extent, and Mg’s solubility (70%) is much higher than that of Ag (0.5%). Higher solubility means the electrochemical potential of the interlayer has a wider range while maintaining Li solid solution phase (BCC). When the interlayer lithiates, metal nanoparticles initially become lithium alloy, and the composition gradually shifts towards a Li solid solution (BCC phase). When the Ag-C interlayer contacts with a Li source, Ag and Li inter-diffuse within Ag-C, forming a percolated network that facilitates Li transport as shown in FIG. 6A. The Ag-C volume remains relatively stable as excess Ag diffuses into the Li metal anode. This is due to Ag’s high diffusivity in Li metal (5. Ox 10 ¹¹ cm²/s) compared to Li’s self-diffusivity ( 1 ,3x 10 ¹² cm²/s). In contrast, when Mg-C contacts the Li source, the Mg particles increase in size due to Mg’s much lower diffusivity in Li (2.1xl0 ¹³ cm²/s), driving unidirectional Li flux into Mg. The Mg particles in Mg-C interlayer expand and become interconnected, while the binder provides a flexible carbon matrix that maintains the structural integrity of the composite.

[0085] Despite the different lithiation mechanisms, both Ag-C and Mg-C facilitate Li transport towards the metal anode. FIG. 6B shows the voltage profile and its derivative during lithiation of an Ag-C interlayer. Ag particles undergo multiple phase transitions during lithiation, and eventually reach a Li solid solution phase just above 0 V. This suggests that inhomogeneous nucleation of Li is not likely to happen since Li will alloy with Ag before nucleating at 0 V. Similarly, in the Mg-C interlayer, Mg phase (HCP phase) directly transforms to Li phase (BCC phase) at an early stage, and lithium directly grows out as a solid solution without overcoming additional nucleation barriers.

[0086] The differential capacity profile of Mg-C interlayer in FIG. 6C shows one peak corresponding to (Mg)-to-(Li) phase transition occurring at around 0.3 V. This suggests that, as long as the overpotential in interlayer remains below 0.3 V, Li will uniformly deposit as Li solid solution (BCC phase). The ability to allow uniform deposition at higher overpotential indicates that the interlayer survives higher current density and is less likely to fail under the same cycling conditions. Because of its high solubility in lithium, magnesium stands out as a promising candidate for the MIEC interlayer.

[0087] The preparation of Mg-C interlayers may require special conditions. Different from Ag, Mg nanoparticles are highly reactive with air and moisture, which requires inert-atmosphere handling. Moreover, conventional grinding or milling approaches cannot downsize Mg due to its ductile nature. The Mg-containing MIEC interlayer was prepared either by simple mixing or a precipitation method. For simple mixing, commercial Mg nanopowders (1-1000 nm, prepared by atomization method) were mechanically mixed with amorphous carbon, binder (polyvinylidene fluoride, PVdF) and solvent (N- methylpyrrolidone, NMP). The slurry was tape-casted on Ni foil and eventually transfer-printed onto a solid electrolyte with a hydraulic or isostatic press.

[0088] For the electroplating method, a porous carbon base layer was first prepared by slurry-casting. Amorphous carbon nanoparticles and PVdF binder were dissolved in NMP, and then casted on a metal substrate, such as Ni or Cu. Next, Mg was electrochemically plated on carbon film in all-phenyl complex electrolyte (AICI3 and CeHsMgCl dissolved in tetrahydrofuran, THF) from a magnesium metal counter electrode, at current densities of 0.1-1 mA cm ².

[0089] Other electrolytes with Mg salt solvated in organic solvent also functions similarly. The mass ratio of Mg and C is 1:30 to 1:8, a value much lower than values reported in the literature. After washing in organic solvent (THF) to remove excess electrolyte salt, a Mg-C interlayer was vacuum- dried overnight. The as-prepared Mg-C interlayer can be directly used in the fabrication of ASSBs.

[0090] After preparation of the solid electrolyte layer, a composite cathode and a Mg-C interlayer were attached to two sides and densified with hydraulic press or isostatic press. A piece of thin Li metal was attached to the Mg-C interlayer after removal of the metal substrate. The fabricated ASSB was tested in a constant-temperature oven. In another example, the as-prepared Mg-C interlayer can be directly used in the fabrication of ASSBs with oxide-based solid electrolytes (e.g., lithium lanthanum zirconium oxide, LLZO). In another example, the as-prepared Mg-C interlayer can be directly used in the fabrication of ASSBs with polymer solid electrolytes (e.g., PEO).

[0091] Example 1.1. Formation of a cathode layer

[0092] Composite cathodes were prepared using a dry process. The cathode active material (e.g., LiNio.83Mno.11Coo.06O2), solid electrolyte (LiePSsCl), and vapor- grown carbon fiber powders were hand-milled at a mass ratio of 70:27:3 with an agate mortar and pestle for 15 minutes until a homogenous mixture was achieved. Next, 0.5 wt% of polytetrafluoroethylene (PTFE) powder was added and hand-milled for another 30 minutes. During the hand-milling process with PTFE, the materials adhered together, forming a homogeneous and malleable paste under shear force. The paste was then subjected to shear-rolling between two metal sheets until a desired loading (20 mg cm ²) was achieved.

[0093] Example 1.2. Formation of an interlayer by direct mixing [0094] In this Example, Mg-C was prepared by physically mixing Mg and C nanoparticles. A slurry for the interlayer was prepared by physically mixing nano-silver particles (~800 nm in diameter), C65 nanocarbon particles at 1:15 by weight, then mixing with a solvent N-methyl-2-pyrrolidone (NMP) and PVDF (7 wt%) using a planetary mixer. After coating the slurry onto a 10-pm-thick Ni foil using a doctor blade, it was dried in Ar at 80 °C for 20 minutes, followed by further drying under vacuum at 100 °C for 12 hours. The thickness of the Mg-C nanocomposite layer was 5-10 pm.

[0095] Example 1.3. Formation of an interlayer by electrochemical deposition

[0096] In Example 1.3, Mg-C was prepared by depositing Mg onto C film. First, a porous carbon coating was prepared by slurry casting. C65 nanocarbon particles were mixed with solvent N-methyl- 2-pyrrolidone (NMP) and PVDF (7 wt%) using planetary mixer. After coating the slurry onto a 10- pm-thick Ni foil using a doctor blade, it was dried in air at 80 °C for 20 minutes, followed by further drying under vacuum at 100 °C for 12 hours. The thickness of the porous carbon film was 5-10 pm and the mass was around 1-1.28 mg/cm². Then, Mg was plated in porous carbon film using Mg metal as counter electrode and all-phenyl complex electrolyte as electrolyte. The electrolyte composition is 0.4 M phenyl magnesium chloride and 0.2 M aluminum trichloride dissolved in tetrahydrofuran (THF). The current density is 1 mA cm^-2 and the duration was 0.1-0.128 hour. Then, the film was washed with THF twice and vacuum-dried.

[0097] Example 1,4, Fabrication of pellet-type solid-state batteries

[0098] In Examples 1.2 and 1.3, electrochemical tests were carried out in pellet cell format in polyether-ether-ketone (PEEK) die with a diameter of 12.7 mm. Typically, 130 mg sulfide solid electrolyte powder (LiePSsCl) was compressed in the die under 150 MPa to form a pellet. A dryprocess composite cathode (17.8 mg active material, 2.8 mAh cm ²) and Mg-C interlayer on Ni substrate were placed on both sides of the solid electrolyte and further densified at 375 MPa. Ni substrate becomes easily detachable from the rest of the cell. After densification, a piece of ~50 pm Li foil was added between the Ni substrate and interlayer and further pressed at 50 MPa for 10 seconds to improve interfacial contact. The cell is subject to a stack pressure of 14 MPa. The cells were heated at 60 °C for 8 hours, then charge-discharged for 1 hour each at 0.1 mA/cm² for 20 cycles to facilitate lithiation of Mg-C interlayer. Then, the cell was cooled down to 30 °C for further evaluation.

[0099] All evaluations were conducted at a temperature of 30 °C within a climate-controlled oven. Cycling performance is shown in FIG. 3B. Both cells are first charged at a constant current of 0.1 C (0.28 mA cm ²) until 4.25 V and discharged until 2.6 V at the same rate (0.1 C, 0.28 mA cm ²) for two cycles. Then, the current density gradually increased every two cycles, following 0.1 C, 0.2 C, 0.33 C, 0.5 C, and 1 C. The cell with Mg-C enables more than 1200 cycles at a high current density of 1 C (2.8 mA cm ²).

[00100] Without further elaboration, it is believed that one skilled in the art can, using the description herein, utilize the present disclosure to its fullest extent. The embodiments described herein are to be construed as illustrative and not as constraining the remainder of the disclosure in any way whatsoever. While the embodiments have been shown and described, many variations and modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims, including all equivalents of the subject matter of the claims. The disclosures of all patents, patent applications and publications cited herein are hereby incorporated herein by reference, to the extent that they provide procedural or other details consistent with and supplementary to those set forth herein.

Claims

1. An interlayer for a solid-state battery, wherein the interlayer comprises: a plurality of carbon nanomaterials, wherein the carbon nanomaterials are in the form of a substrate; and a plurality of magnesium (Mg) particles uniformly dispersed on the carbon nanomaterials.

2. The interlayer of claim 1, wherein the carbon nanomaterials comprise nanometer- sized dimensions ranging from about 1 nm to about 100 nm, and wherein the carbon nanomaterials are selected from the group consisting of carbon powder, carbon nanoparticles, amorphous carbon, porous carbon, carbon black, Ketjen Black, carbon nanotubes, vapor-grown carbon nanofibers, oxidized carbons, or combinations thereof.

3. The interlayer of claim 1, wherein the Mg particles comprise Mg nanoparticles, wherein the Mg nanoparticles comprise average diameters below 1 pm.

4. The interlayer of claim 1, wherein the Mg particles are operable to undergo a peritectic reaction with lithium (Li), and wherein the metals are soluble in a Li solid solution phase.

5. The interlayer of claim 1, wherein the magnesium: carbon nanomaterial mass ratio ranges between 1:30 to 1:8.

6. The interlayer of claim 1, wherein the diffusivity of metals of the Mg particles in a lithium (Li) solid solution phase is smaller than Li self-diffusivity, and wherein the Mg particles expand upon contact with Li metal.

7. The interlayer of claim 1, wherein the Mg particles expand upon contact with lithium (Li) metal and become interconnected within the interlayer due to volume expansion to form a percolating network, and wherein the percolating network is capable of selectively conducting flow of ions while restricting flow of electrons.

8. The interlayer of claim 1, wherein the interlayer comprises from about 10 wt% to about 90 wt% of the carbon nanomaterials.

9. A solid-state battery comprising: a cathode; a solid electrolyte; a current collector; and an interlayer positioned between the solid electrolyte and the current collector, wherein the interlayer is in contact with the solid electrolyte, and wherein the interlayer comprises: a plurality of carbon nanomaterials, and a plurality of Mg nanoparticles uniformly dispersed on the carbon nanomaterials, wherein the Mg nanoparticles expand upon lithiation, wherein the lithiated interlayer comprises a percolating network operational for regulating ion flux through the interlayer such that the battery is capable of high rate cycling greater than 2.5 mA cm ² at areal capacities greater than 2 mAh cm ² under ambient temperatures of about 30 °C or less.

10. The solid-state battery of claim 9, further comprising an anode positioned between the current collector and the interlayer.

11. The solid-state battery of claim 9, wherein the cathode is a lithium-ion cathode.

12. The solid-state battery of claim 10, wherein the anode comprises lithium metal, wherein metal elements in the interlayer inter-diffuses with the lithium metal, wherein the self-diffusion coefficient of lithium is smaller than the diffusion coefficient of the metal elements in the lithium, and wherein the interdiffusion facilitates the volume expansion of the Mg nanoparticles and subsequent interconnection of the Mg nanoparticles within the interlayer.

13. An anode-free solid-state lithium battery comprising: a cathode; an electrolyte in contact with the cathode; a current collector; and an interlayer positioned between the current collector and the solid electrolyte, wherein the interlayer comprises: a plurality of carbon nanomaterials, wherein the carbon nanomaterials are in the form of a substrate, and a plurality of Mg nanoparticles, wherein the Mg nanoparticles are uniformly dispersed throughout the carbon nanomaterial substrate to form a percolating network, wherein the percolating network is operable to regulate lithium ion flux through the interlayer.

14. A method of forming an interlayer comprising a percolating network capable of regulating ion flux therethrough, the method comprising: associating a plurality of Mg nanoparticles with a plurality of carbon nanomaterials, wherein the carbon nanomaterials are in the form of a substrate and comprise nanometer- sized dimensions, wherein the Mg nanoparticles become uniformly integrated in the carbon nanomaterial substrate, and wherein the associating results in the formation of a uniform Mg nanoparticle-carbon nanomaterial substrate composite.

15. The method of claim 14, wherein the associating step occurs by a method selected from the group consisting of chemical precipitation, electrochemical deposition, ultrasonication, thermal decomposition, or a combination thereof.

16. The method of claim 14, wherein the Mg nanoparticles comprise diameters between about 5 nm to about 1000 nm.

17. A method of forming a solid-state battery, comprising: attaching an interlayer to a solid electrolyte, wherein the solid electrolyte is attached to a cathode, and wherein the interlayer comprises: a plurality of carbon nanomaterials, wherein the carbon nanomaterials are in the form of a substrate, a plurality of Mg nanoparticles uniformly dispersed on the carbon nanomaterials, wherein the Mg nanoparticles form a coating on the carbon nanomaterials without aggregating, and a percolating network operable for regulating an ion flux therethrough; and attaching an anode to the interlayer, wherein the anode comprises a current collector, and optionally a layer of anode metal.

18. A method of forming a solid-state battery, comprising: attaching an interlayer to a surface of an anode to form an anode-interlayer assembly, wherein the interlayer comprises: a plurality of carbon nanomaterials, wherein the carbon nanomaterials are in the form of a substrate, a plurality of Mg nanoparticles uniformly dispersed on the carbon nanomaterials, wherein the Mg nanoparticles expand upon contact with a lithium source and become interconnected to form a percolating network operable for regulating an ion flux therethrough; and attaching the anode-interlayer assembly to a solid electrolyte-cathode assembly to form an anode-interlayer- solid-electrolyte-cathode assembly.

19. The method of claim 18, wherein the anode comprises lithium.