CN120600905A

CN120600905A - Electrolytes, batteries and electrical equipment

Info

Publication number: CN120600905A
Application number: CN202510769507.1A
Authority: CN
Inventors: 史勇; 许铃鸿; 吴坚; 应杭君; 唐吉林
Original assignee: Guangzhou Automobile Group Co Ltd
Current assignee: Guangzhou Automobile Group Co Ltd
Priority date: 2025-06-09
Filing date: 2025-06-09
Publication date: 2025-09-05

Abstract

The embodiments of the present application provide an electrolyte, a battery and an electrical device, wherein the electrolyte includes a lithium salt, an organic solvent and a polymer matrix, and the monomers of the polymer matrix include vinylene carbonate and ethyl isocyanate acrylate. In the electrolyte provided in the embodiments of the present application, the monomers of the polymer matrix include vinylene carbonate and ethyl isocyanate acrylate, wherein the low HOMO energy level of ethyl isocyanate acrylate can weaken the electron loss ability of the polymer matrix, improve the oxidative stability of the electrolyte, and thus improve the poor electrochemical stability; and the copolymerization structure of vinylene carbonate and ethyl isocyanate acrylate reduces the crystallinity of the polymer matrix, providing a smoother path for Li ⁺ transmission, thereby improving the ionic conductivity of the electrolyte. Therefore, the electrolyte proposed in the present application can effectively improve the problems of low room temperature ionic conductivity and poor electrochemical stability of existing gel electrolytes, and has good application prospects.

Description

Electrolyte, battery and electric equipment

Technical Field

The application relates to the technical field of batteries, in particular to an electrolyte, a battery and electric equipment.

Background

At present, the gel electrolyte prepared by the in-situ polymerization method can effectively improve the physical contact between an electrode and an electrolyte interface, reduce interface impedance, and is compatible with the existing lithium ion battery manufacturing process, so that the gel electrolyte becomes one of solid electrolyte materials with the highest scale potential.

However, the existing gel electrolyte still has the conditions of low ionic conductivity at room temperature, narrow electrochemical window, serious interface side reaction and the like.

Based on this, development of an electrolyte is needed to solve the problems of low ionic conductivity and poor electrochemical stability of the gel electrolyte at room temperature.

Disclosure of Invention

The embodiment of the application provides an electrolyte, a battery and electric equipment, and aims to solve the problems of low ionic conductivity and poor electrochemical stability of the conventional gel electrolyte at room temperature.

In order to solve the problems, the application is realized by the following technical scheme:

The application provides an electrolyte, which comprises lithium salt, an organic solvent and a polymer matrix, wherein monomers of the polymer matrix comprise vinylene carbonate and isocyanate ethyl acrylate.

In the electrolyte provided by the embodiment of the application, the low HOMO energy level of the isocyanate ethyl acrylate can weaken the electron losing capability of the polymer matrix, and improve the oxidation stability of the electrolyte, so that the poor electrochemical stability is improved, and the copolymerization structure of the ethylene carbonate and the isocyanate ethyl acrylate reduces the crystallinity of the polymer matrix, so that a smoother path is provided for Li ⁺ transmission, and the ion conductivity of the electrolyte is improved. Therefore, the electrolyte provided by the application can effectively solve the problems of low ionic conductivity and poor electrochemical stability of the conventional gel electrolyte at room temperature, and has good application prospect.

Further, in the electrolyte, the lithium salt comprises lithium bis (trifluoromethanesulfonyl) imide and lithium difluorooxalato borate, and the molar ratio of the lithium bis (trifluoromethanesulfonyl) imide to the lithium difluorooxalato borate is (3-5): 1.

Further, in the electrolyte, the organic solvent comprises trimethyl phosphate and fluoroethylene carbonate, and the mass ratio of the trimethyl phosphate to the fluoroethylene carbonate is (2:3) - (3:2).

Further, the electrolyte is a gel electrolyte, and the electrolyte further comprises a cross-linking agent and/or an initiator;

the cross-linking agent comprises at least one of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, ethoxylated trimethylolpropane triacrylate and methylenebisacrylamide;

The initiator includes at least one of azobisisobutyronitrile, dibenzoyl peroxide, and azobisisoheptonitrile.

Further, in the organic solvent, the mass ratio of the trimethyl phosphate to the fluoroethylene carbonate is (2:3) - (3:2).

Further, the mole fraction of the crosslinking agent is 0.8-1.2% based on the total mole of monomers of the polymer matrix.

Further, the mass fraction of the initiator is 0.3-1% based on the total mass of the monomers of the polymer matrix.

Further, the mass ratio of the monomer of the polymer matrix to the lithium salt is (3-10): 1.

The application also provides a battery, which comprises a positive electrode plate, a negative electrode plate and the electrolyte.

The negative electrode sheet comprises metallic lithium, and/or

The positive electrode active material of the positive electrode plate comprises a lithium-rich manganese-based layered oxide.

The application also provides electric equipment, which comprises the battery, wherein the battery is used as a power supply of the electric equipment.

Drawings

FIG. 1 is a Fourier transform infrared spectrum of the electrolyte in test example 1 and test example 2;

FIG. 2 is a scanning electron microscope topography of the electrolyte of test example 1 and test example 2;

FIG. 3 is an X-ray energy spectrum of the electrolyte energy dispersion type in test example 1;

FIG. 4 is an X-ray energy spectrum of the electrolyte energy dispersion type in test example 2;

FIG. 5 is a graph showing the analysis of Li+ conductivity of the electrolyte in test example 1 and test example 2;

FIG. 6 is a graph showing the analysis of the Li+ migration number of the electrolyte in test example 1 and test example 2;

FIG. 7 is an electrochemical impedance spectrum of the cells of test example 3 and test example 4;

FIG. 8 is a cloud of dynamic relaxation time distributions of the cells of test example 3 and test example 4;

FIG. 9 is an analysis chart of the activation energy of the batteries in test example 3 and test example 4;

FIG. 10 is an electrochemical window analysis of the electrolytes of test example 5 and test example 6;

FIG. 11 is a graph showing the cycle performance of the cells of test example 3 and test example 4 at 0.5mA cm ^-2 and 0.5mAh cm ^-2;

FIG. 12 is a graph showing the rate performance of the batteries of test example 3 and test example 4;

FIG. 13 is a scanning electron microscope image of the lithium anode after cycling of the battery in test example 3 and test example 4;

Fig. 14 is a graph showing the cycle performance of the batteries of example 1 and comparative example 1 under 0.2C operating conditions;

Fig. 15 is a graph of the battery rate performance in example 1 and comparative example 1;

FIG. 16 is a cyclic voltammogram of example 1 and comparative example 1;

fig. 17 is a cycle performance test of the batteries of example 2 and example 3 under 0.2C operating conditions.

Detailed Description

In order to make the technical problems, technical schemes and beneficial effects solved by the application more clear, the application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.

Lithium Ion Batteries (LIBs) generally employ graphite cathodes, layered oxide anodes, and organic liquid electrolytes, which are difficult to overcome low energy density (< 300 Wh/kg) and thermal runaway risks, and cannot meet the requirements of the electronics and automotive industries for safety and efficiency of energy storage devices. While the combination of lithium metal negative electrodes (theoretical capacity 3860 mAh/g) and solid state electrolytes is considered as the core direction of the next generation battery technology, the development of the lithium metal negative electrodes is limited by the problems of lithium dendrite growth, unstable electrolyte/electrode interface layers and the like.

The applicant finds that the use of a high modulus, non-flammable solid electrolyte instead of a flammable organic liquid electrolyte has proven to be an effective solution to overcome the limitations of lithium metal cathodes and significantly improve battery safety, making solid lithium metal batteries a very promising solution in advanced battery technology. The electrolyte prepared by the in-situ polymerization method can effectively improve the physical contact between the electrode and the electrolyte interface, reduce the interface impedance, and is compatible with the existing lithium ion battery manufacturing process, so that the electrolyte becomes one of solid electrolyte materials with the highest scale potential. However, the existing electrolyte still has the problems of low ionic conductivity at room temperature, narrow electrochemical window, serious interface side reaction and the like.

Therefore, the gel polymer electrolyte which can be efficiently compatible with lithium metal cathode and high-voltage cathode materials and has good ion transmission performance has positive significance in promoting the development of solid-state lithium metal batteries and polymer solid-state electrolytes.

Based on the above findings, the embodiments of the present application provide an electrolyte including a lithium salt, an organic solvent, and a polymer matrix whose monomers include Vinylene Carbonate (VC) and ethyl isocyanate acrylate (ICA) in order to solve the problems of low ionic conductivity and poor electrochemical stability at room temperature of the above electrolyte. In the electrolyte provided by the embodiment of the application, the HOMO (highest occupied molecular orbital) energy level of isocyanate ethyl acrylate as low as 7.68eV can weaken the electron losing capability of a polymer matrix, improve the oxidation stability of the electrolyte, so that the electrochemical stability is poor, and the copolymerization structure of ethylene carbonate and isocyanate ethyl acrylate reduces the crystallinity of the polymer matrix, provides a smoother path for Li ⁺ transmission, and further improves the ionic conductivity of the electrolyte. Therefore, the electrolyte provided by the application can effectively solve the problems of low ionic conductivity and poor electrochemical stability of the conventional gel electrolyte at room temperature, and has good application prospect.

In one embodiment, the battery electrolyte may be detected by infrared testing to include components such as vinylene carbonate and isocyanate ethyl acrylate.

Optionally, in an embodiment, in the electrolyte provided by the embodiment of the application, the mass ratio of the vinylene carbonate to the isocyanate ethyl acrylate is (2:3) - (3:2), so that the balance of high-voltage stability and ionic conductivity of the electrolyte can be realized. In some embodiments, the mass ratio of vinylene carbonate to isocyanate ethyl acrylate may be in the range of values of one or any two of 3:2, 3:3, 2:3.

In the electrolyte provided by the embodiment of the invention, the lithium salt comprises one or more of lithium bis (fluorosulfonyl) imide salt, lithium bis (trifluoromethane sulfonate) imide, lithium tetrafluoroborate, lithium perchlorate and lithium trifluoromethane sulfonate, and can be matched with the polymer matrix to form the interface film which is favorable for ion conduction and rich in lithium nitrogen compounds.

Alternatively, in one embodiment, the above lithium salts include lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) and lithium difluorooxalato borate (LiDFOB).

In the embodiment, the lithium bistrifluoromethane sulfonyl imide and the lithium difluorooxalato borate are used as lithium salts, and the LUMO-HOMO (lowest unoccupied molecular orbital-highest occupied molecular orbital) energy gap of the lithium difluorooxalato borate as narrow as 5.13eV can promote the preferential decomposition of the lithium difluorooxalato borate on the surface of an electrode to form inorganic components rich in B-O and B-F, so that a Li+ transmission path is optimized, a compact and stable interface layer is formed, and an electrolyte forms a solid electrolyte interface film (Solid Electrolyte Interphase, SEI) and a positive electrode electrolyte interface film (Cathode Electrolyte Interphase, CEI) which are rich in inorganic components and compact and stable on the surfaces of a lithium metal negative electrode and a lithium manganese-rich basal layer oxide, thereby not only promoting the uniform deposition of lithium, inhibiting the growth of dendrites, but also greatly reducing the side reaction of the interface, and enabling the assembled solid lithium metal battery to show excellent high-voltage cycle stability and interface dynamics.

Optionally, in one embodiment, in the electrolyte provided by the embodiment of the application, the molar ratio of the lithium bistrifluoromethane sulfonyl imide serving as the lithium salt to the lithium difluorooxalic acid borate is (3-5): 1, and the electrode/electrolyte interface phase formed under the molar ratio is moderate in thickness and good in interface stability. In some embodiments, the molar ratio of lithium bistrifluoromethane sulfonimide to lithium difluorooxalato borate may be in the range of values of one or any two of 3:1, 4:1, 5:1.

Optionally, in one embodiment, the mass ratio of the monomer of the polymer matrix to the lithium salt is (3-10): 1, so that the electrolyte can effectively achieve excellent ionic conductivity, high-pressure cycle stability and interfacial kinetics.

In some embodiments, the mass ratio of monomer to lithium salt of the polymer matrix described above may be in the range of one or any two of 3 _:1、5_:1、10_: <1 >.

Optionally, in the electrolyte solution of the secondary battery provided by the embodiment of the invention, the concentration of the lithium salt is 0.5-2 mol/L, and may be, for example, one or any two of 0.5mol/L, 1mol/L, 1.5mol/L and 2 mol/L. In the above range, the lithium salt concentration not only effectively constructs a solid electrolyte interface mainly composed of inorganic components, but also avoids the problem of decrease in ionic conductivity due to increase in the viscosity of the electrolyte.

Alternatively, in one embodiment, the organic solvent includes trimethyl phosphate and fluoroethylene carbonate.

In the embodiment, trimethyl phosphate (TMP) and fluoroethylene carbonate (FEC) are used as solvents in the electrolyte, wherein the introduction of fluoroethylene carbonate can further increase the content of LiF in the SEI on the surface of a lithium metal negative electrode, reduce the Li+ diffusion barrier, enable the room-temperature ion conductivity of the electrolyte to reach 0.12mS cm ^-1, and enable the Li+ migration number to be increased to 0.435, effectively relieve the concentration polarization phenomenon, enhance the mechanical strength and the ion transmission capacity of an interface, and the entering of trimethyl phosphate can improve the flame retardance and the ion transmission performance of the electrolyte.

Optionally, in one embodiment, the mass ratio of trimethyl phosphate to fluoroethylene carbonate as the organic solvent is (2:3) - (3:2), and the formed electrolyte can have better flame retardance, ion transmission performance and lithium stability. In some embodiments, the mass ratio of trimethyl phosphate to fluoroethylene carbonate may be in the range of one or any two of 3:2, 3:3, 3:2.

Optionally, in one embodiment, the electrolyte further includes a crosslinking agent, the crosslinking agent including at least one of polyethylene glycol diacrylate (PEGDA), polyethylene glycol dimethacrylate (PEGDMA), polypropylene glycol diacrylate (PPGDA), ethoxylated Trimethylol Propane Triacrylate (ETPTA), and Methylenebisacrylamide (MBA);

in the embodiment, the cross-linking agent is introduced into the electrolyte, so that the cross-linking agent can be efficiently cross-linked with double bonds in ethylene carbonate and isocyanate ethyl acrylate to form a stable three-dimensional interconnected network, and the mechanical strength of the electrolyte is improved.

Alternatively, in some embodiments, the cross-linking agent is polyethylene glycol diacrylate (PEGDA). The terminal of the polyethylene glycol diacrylate ester chain segment contains two acrylate groups, can be efficiently crosslinked with double bonds in ethylene carbonate and isocyanate ethyl acrylate monomers to form a stable three-dimensional interconnected network, improves the mechanical strength of electrolyte, meanwhile, the polyethylene glycol chain segment (-CH ₂CH₂ O-) in the polyethylene glycol diacrylate ester can endow the electrolyte with good flexibility, is beneficial to good interface contact between the electrolyte and an electrode material, and in addition, the compatibility of the polyethylene glycol diacrylate ester with ethylene carbonate, isocyanate ethyl acrylate monomers and other monomers and trimethyl phosphate, fluoroethylene carbonate and other solvents is good, so that the polyethylene glycol diacrylate ester can be uniformly distributed in electrolyte slurry, and the uniformity of the electrolyte component structure is improved.

The electrolyte provided by the embodiment of the application can be specifically gel electrolyte. Optionally, in one embodiment, the electrolyte further includes an initiator including at least one of Azobisisobutyronitrile (AIBN), dibenzoyl peroxide (BPO), and Azobisisoheptonitrile (ABVN).

In the embodiment, the initiator can crack at a lower temperature of 60-80 ℃ to generate a free radical active center, promote chain polymerization reaction of vinylene carbonate and isocyanate ethyl acrylate, and has high initiation efficiency.

Optionally, in one embodiment, the molar fraction of the crosslinking agent is 0.8-1.2% based on the total monomer mole of the polymer matrix, so that the mechanical strength of the electrolyte and the interface contact between the electrolyte and the electrode can be effectively balanced, and the growth of lithium dendrites can be inhibited.

In some embodiments, the mole fraction of the above-described crosslinking agent may be in the range of values of one or any two of 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, based on the total moles of monomers of the polymer matrix.

Optionally, in some embodiments, the initiator is Azobisisobutyronitrile (AIBN), which not only can be cracked at a lower temperature of 60-80 ℃ to generate a free radical active center and promote chain polymerization reaction of vinylene carbonate and isocyanate ethyl acrylate, and has higher initiation efficiency, but also has less influence on chemical stability of an electrolyte system (such as lithium salt and solvent) due to nitrogen and a small amount of low-toxicity isobutyronitrile as an azobisisobutyronitrile decomposition product, so that introduction of harmful impurities is avoided.

Optionally, in some embodiments, the mass fraction of the initiator is 0.3-1% based on the total mass of the monomers of the polymer matrix, so that not only enough free radicals can be provided, but also the mechanical strength and chemical stability of the electrolyte are prevented from being reduced due to the fact that unpolymerized monomers remain, and the initiator or byproducts thereof are prevented from remaining in the electrolyte, so that interface side reactions are caused, and the cycle stability of the battery is deteriorated.

In some embodiments, the mass fraction of the initiator is in the range of one or any two of 0.3%, 0.5%, 1.0% based on the total moles of monomers of the polymer matrix.

In a specific embodiment, the electrolyte provided in the embodiment of the application uses VC and ICA copolymer as monomers, liTFSI and LiDFOB as lithium salt, PEGDA as a cross-linking agent, and AIBN as an initiator.

In the embodiment of the application, the polymer matrix and the electrolyte components of the electrolyte are synergistically optimized by adopting a bi-component synergistic modulation strategy, so that the electrochemical window of the electrolyte is widened, the compatibility of the electrolyte/electrode interface is improved, and the stability of the solid-state lithium metal battery in circulation and the stable improvement of the rate capability are promoted.

The low HOMO energy level of the isocyanate ethyl acrylate can weaken the electron losing capability of a polymer matrix, improve the oxidation stability of electrolyte, and promote the preferential decomposition of lithium difluoro oxalate borate on the surface of an electrode to form a compact and stable interface layer. Meanwhile, the introduction of fluoroethylene carbonate further increases the content of LiF in the SEI on the surface of the lithium metal negative electrode, and enhances the mechanical strength and the ion transmission capability of the interface. In addition, the copolymerized structure of vinylene carbonate and isocyanate ethyl acrylate reduces the crystallinity of the polymer matrix, providing a smoother path for Li ⁺ transport. Thanks to this, the above electrolyte forms an inorganic component-rich and compact stable SEI and CEI layer on the surfaces of a lithium metal anode and a 4.6V LRMO (lithium-rich manganese-based cathode material) cathode, which not only promotes uniform deposition of lithium, suppresses dendrite growth, but also greatly reduces interfacial side reactions, so that the assembled solid lithium metal battery exhibits excellent high-voltage cycle stability and interfacial kinetics.

The electrolyte provided by the embodiment of the application can construct a stable interface layer in situ on the surfaces of a lithium metal anode and an LRMO anode, wherein a decomposition product (B-O, B-F) of LiDFOB and FEC derived LiF form SEI and CEI layers with high mechanical strength and ion conductivity together, and lithium dendrite growth and interface side reaction are effectively inhibited.

The electrolyte provided by the embodiment of the application has excellent high-voltage stability, the electrochemical window exceeds 5.1V (vs. Li ⁺/Li), and the application requirement of the 4.6V-level LRMO anode can be met. Meanwhile, the synergistic effect of LiDFOB and FEC forms a CEI layer rich in B-O, B-F and LiF at the interface of the positive electrode, thereby obviously reducing side reaction of electrolyte and ensuring long-term circulation stability under high pressure. The electrolyte-based solid-state lithium battery can maintain 99.75% of initial coulombic efficiency and 76.8% of capacity retention after 100 cycles at a high voltage of 4.6V.

In addition, the electrolyte provided by the embodiment of the application can be prepared by adopting an in-situ thermal polymerization process, the polymerization temperature is only 70 ℃, the process is simple, and the energy consumption is low. In addition, the cost of the electrolyte raw material is controllable, and the potential of large-scale production is provided.

The embodiment of the application provides a preparation method of an electrolyte, as shown in fig. 1, the method comprises the following steps of 101-103:

step 101, mixing a monomer of a polymer matrix with a cross-linking agent to obtain first slurry, wherein the monomer of the polymer matrix comprises vinylene carbonate and isocyanate ethyl acrylate;

102, mixing lithium salt with an organic solvent to obtain second slurry;

step 103, mixing the first slurry with the second slurry, and adding an initiator to obtain the electrolyte.

In the embodiment of the application, the electrolyte is prepared through steps 101 to 203 by adopting an in-situ thermal polymerization process, wherein ethylene carbonate and ethyl isocyanate acrylate are used as polymer monomers, the low HOMO energy level of the ethyl isocyanate acrylate can weaken the electron loss capability of a polymer matrix, and the oxidation stability of the electrolyte is improved, so that the poor electrochemical stability is improved, and the copolymerization structure of the ethylene carbonate and the ethyl isocyanate acrylate reduces the crystallinity of the polymer matrix, and provides a smoother path for Li ⁺ transmission, so that the ion conductivity of the electrolyte is improved.

Therefore, the electrolyte prepared by the application can effectively solve the problems of low ionic conductivity and poor electrochemical stability of the existing electrolyte at room temperature, and has good application prospect.

In addition, in the preparation process, the polymerization temperature is as low as 70 ℃, the process is simple, the energy consumption is low, the cost of the electrolyte raw materials is controllable, and the method is suitable for large-scale production.

Optionally, in the step 101, after adding the crosslinking agent to the monomer of the polymer matrix, the mixture may be uniformly mixed by stirring, where the stirring time may be one or any two of 1h, 2h, 6h and 12h, and the mass ratio of the vinylene carbonate to the isocyanate ethyl acrylate is (2:3) - (3:2), so as to achieve balance between high-voltage stability and ionic conductivity of the electrolyte. In some embodiments, the mass ratio of vinylene carbonate to isocyanate ethyl acrylate may be in the range of values of one or any two of 3:2, 3:3, 3:2.

Optionally, in the step 101, the crosslinking agent includes at least one of polyethylene glycol diacrylate (PEGDA), polyethylene glycol dimethacrylate (PEGDMA), polypropylene glycol diacrylate (PPGDA), ethoxylated trimethylolpropane triacrylate (ETPTA), and Methylenebisacrylamide (MBA);

the addition amount of the cross-linking agent is 0.8-1.2% of the total mole of the monomers of the polymer, so that the mechanical strength of the electrolyte and the interface contact between the electrolyte and the electrode can be balanced, and the growth of lithium dendrites can be inhibited.

Optionally, the cross-linking agent may be polyethylene glycol diacrylate (PEGDA), and the PEGDA does not undergo thermal decomposition reaction at the thermal polymerization reaction temperature (70 ℃), so that the content of PEGDA in the product is still maintained at 0.8-1.2 mol% of the monomer of the polymer.

In the preparation method provided by the embodiment of the invention, in the step 102, after the lithium salt is added into the organic solvent, the organic solvent is uniformly mixed by stirring and the like, wherein the stirring time can be one or any two of the range values of 1h, 2h, 6h and 12h, and the lithium salt comprises one or more of lithium difluorosulfimide salt, lithium bistrifluoromethanesulfonate imide, lithium tetrafluoroborate, lithium perchlorate and lithium trifluoromethane sulfonate, and can be matched with the polymer matrix to form the interfacial film which is favorable for ion conduction and contains the lithium nitrogen compound.

Alternatively, in one embodiment, in step 102 above, the lithium salt includes lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) and lithium difluoro (lidadiob) oxalato borate (litdiob).

Optionally, in the step 102, the molar ratio of lithium bistrifluoromethane sulfonyl imide to lithium difluoro oxalato borate is (3-5): 1, and the electrode/electrolyte interface phase formed by the molar ratio is moderate in thickness and good in interface stability. In some embodiments, the molar ratio of lithium bistrifluoromethane sulfonimide to lithium difluorooxalato borate may be in the range of values of one or any two of 3:1, 4:1, 5:1.

Optionally, in one embodiment, in the step 102, the mass ratio of the monomer of the polymer matrix to the lithium salt is controlled to be (3-10): 1, so that the electrolyte can effectively achieve excellent ionic conductivity, high-pressure cycle stability and interfacial kinetics.

Optionally, in an embodiment, in the step 102, the concentration of the lithium salt is controlled to be 0.5 to 2mol/L, for example, one or any two of 0.5mol/L, 1mol/L, 1.5mol/L, and 2mol/L may be used. In the above range, the lithium salt concentration not only effectively constructs a solid electrolyte interface mainly composed of inorganic components, but also avoids the problem of decrease in ionic conductivity due to increase in the viscosity of the electrolyte.

Optionally, in the step 102, the organic solvent includes trimethyl phosphate and fluoroethylene carbonate, and the mass ratio of trimethyl phosphate to fluoroethylene carbonate is controlled to be (2:3) - (3:2), so that the formed electrolyte has better flame retardance, ion transmission performance and good lithium stability. In some embodiments, the mass ratio of trimethyl phosphate to fluoroethylene carbonate may be in the range of one or any two of 3:2, 3:3, 3:2.

Optionally, in step 103, the initiator includes at least one of Azobisisobutyronitrile (AIBN), dibenzoyl peroxide (BPO), and Azobisisoheptonitrile (ABVN).

Optionally, in the step 103, the addition amount of the initiator is 0.3-1% of the total monomer mass of the polymer matrix, so that enough free radicals can be provided, the residual unpolymerized monomer is avoided to reduce the mechanical strength and chemical stability of the electrolyte, and the initiator or the byproducts thereof are prevented from remaining in the electrolyte to cause interface side reactions, thereby deteriorating the cycle stability of the battery.

The embodiment of the application also provides a battery, which comprises a positive electrode plate, a negative electrode plate and the electrolyte.

Alternatively, in one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium ion transition metal oxide. The lithium ion transition metal oxide comprises at least one of nickel cobalt lithium manganate, lithium cobaltate, lithium manganate and lithium iron phosphate.

Optionally, in one embodiment, the positive electrode active material includes a lithium-rich manganese-based layered oxide (LRMO), so that not only the advantages of a higher theoretical specific capacity (> 300mAh g ^-1) and a higher upper operating voltage limit (> 4.8V) of the lithium-rich manganese-based layered oxide can be fully exerted, but also an inorganic-rich and compact stable CEI layer can be formed on the 4.6V LRMO positive electrode surface by using the electrolyte in situ, which not only promotes uniform deposition of lithium, inhibits dendrite growth, but also greatly reduces interface side reactions, so that the assembled solid-state lithium metal battery exhibits excellent high-voltage cycling stability and interface dynamics.

Symmetrical battery tests show that the electrolyte can enable the critical current density of lithium deposition to reach 4.0mA cm ^-2, realize stable circulation for more than 500 hours under the condition of 0.5mA cm ^-2, and has the activation energy as low as 0.70eV, which is obviously superior to the traditional polymer electrolyte.

In the battery provided by the embodiment of the application, the positive electrode plate further comprises a conductive agent and a binder, optionally, the conductive agent comprises at least one of conductive carbon black, acetylene black, ketjen black, carbon nanotubes and graphene, and the binder comprises at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer and a tetrafluoroethylene-hexafluoropropylene copolymer.

In some embodiments, the positive electrode sheet is prepared by dispersing the above components for preparing the positive electrode sheet, including the above positive electrode material, an adhesive and any other components, in a solvent such as N-methylpyrrolidone to form a positive electrode slurry, coating the positive electrode slurry on both sides of a positive electrode current collector such as aluminum foil, and baking, rolling, cutting, and slitting the positive electrode sheet.

The secondary battery provided by the embodiment of the invention further comprises a diaphragm.

In some embodiments, the negative electrode sheet is a metallic lithium sheet.

Meanwhile, the electrolyte is utilized to construct and form solid SEI rich in inorganic components and compact and stable on the surface of the lithium metal negative electrode in situ, so that the uniform deposition of lithium is promoted, the growth of dendrites is inhibited, the side reaction of an interface is greatly reduced, and the assembled solid lithium metal battery shows excellent high-voltage cycle stability and interface dynamics.

In other embodiments, the negative electrode tab includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, where the negative electrode active material layer may employ a negative electrode active material for a battery, and the negative electrode active material includes any one or a combination of at least two of hard carbon, soft carbon, graphite, and silicon oxide.

In the case that the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, the negative electrode sheet is prepared by dispersing the components for preparing the negative electrode sheet, such as the negative electrode active material, the adhesive and the conductive agent, in a solvent such as deionized water to form negative electrode slurry, coating the negative electrode slurry on two sides of the negative electrode current collector such as copper foil, and baking, rolling, cutting, slitting and the like.

In practical application, the negative electrode plate, the diaphragm and the positive electrode plate are sequentially stacked and wound to obtain a winding core, the winding core is packaged to obtain a bare cell, and the bare cell is baked, injected with liquid, formed, sealed for two times and separated to obtain the secondary battery.

The invention also provides electric equipment, which comprises the battery, wherein the battery is used as a power supply of the electric equipment.

For the above-mentioned embodiments of the electrical equipment, which include the above-mentioned battery and achieve the same technical effects, for avoiding repetition, the description is omitted herein, and the relevant parts only need to refer to the part of the description of the embodiments of the battery.

In order to make the objects, technical solutions and advantageous effects of the present invention clearer, the present invention is further described below with reference to examples. It is to be understood that these examples are illustrative of the present invention and are not intended to limit the scope of the present invention.

The present invention will be described in detail with reference to examples.

Example 1

(1) Electrolyte preparation

S1, mixing a polymer monomer VC and an ICA in a mass ratio of 1:1, adding PEGDA with a monomer concentration of 1mol%, and stirring to obtain a first slurry;

s2, uniformly mixing 0.8M LiTFSI, 0.2M LiDFOB and TMP/FEC (1:1wt%) solvent, stirring to obtain a second slurry;

S3, mixing the first slurry and the second slurry in a mass ratio of 1:1, stirring, adding AIBN initiator accounting for 0.5wt% of the monomer mass, and performing thermal polymerization at 70 ℃ for 2 hours to obtain an electrolyte;

(2) Preparation of positive electrode plate

Uniformly mixing the positive electrode material lithiated manganese oxide, a conductive agent Super P and a binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, adding an NMP solvent, stirring and uniformly mixing under a vacuum condition, coating the slurry on two sides of a carbon-coated aluminum foil with 14um, controlling the surface load to be 2.5mg/cm ², then drying in an oven at a high temperature of 110 ℃, and then rolling, cutting, slitting and the like to obtain the positive electrode plate.

(3) Preparation of negative electrode plate

And selecting a metal lithium sheet as a negative electrode sheet.

(4) Preparation of a Battery

In a glove box with argon and water oxygen values of less than 1ppm, assembling the positive electrode plate prepared in the step (2), the negative electrode plate prepared in the step (3) and the electrolyte prepared in the step (1) by adopting a 2032 type battery shell to obtain a lithium metal full battery, wherein the packaging pressure is 3MPa.

Example 2

Example 2 differs from example 1 in that:

in the step S1, the monomer concentration of which the mass ratio of VC to ICA is 2:3 and the addition amount of PEGDA is 0.8mol% is adjusted;

In the step S2, the addition amount of LiTFSI is adjusted to be 0.6M, and the mass ratio of TMP/FEC is 2:3;

in step S3, the AIBN initiator is adjusted to be added in an amount of 0.3wt% of the monomer mass.

Example 3

Example 3 differs from example 1 in that:

In the step S1, the monomer concentration of which the mass ratio of VC to ICA is 3:2 and the addition amount of PEGDA is 1.2mol% is adjusted;

In the step S2, the addition amount of LiTFSI is adjusted to be 1.0M, and the mass ratio of TMP/FEC is 3:2;

in step S3, the AIBN initiator is adjusted to 1.0wt% monomer mass.

Comparative example 1

Comparative example 1 differs from example 1 in that no ICA monomer was added in step S1, and no lidaob salt and FEC solvent were added in step S2.

Test example 1

The electrolyte prepared in example 1, a working electrode and a reference electrode are assembled in a glove box (H ₂O≤0.1ppm,O₂ is less than or equal to 0.1 ppm) filled with argon atmosphere by adopting 2032 type battery cases to obtain the stainless steel symmetrical battery, wherein the working electrode and the reference electrode are stainless steel sheets, and the packaging pressure is 3MPa.

Test example 2

The electrolyte prepared in comparative example 1, a working electrode and a reference electrode are assembled in a glove box (H ₂O≤0.1ppm,O₂ is less than or equal to 0.1 ppm) filled with argon atmosphere by adopting 2032 type battery cases to obtain a stainless steel symmetrical battery, the working electrode and the reference electrode are stainless steel sheets, and the packaging pressure is 3MPa.

Test example 3

The electrolyte prepared in example 1, a working electrode and a reference electrode are assembled in a glove box (H ₂O≤0.1ppm,O₂ is less than or equal to 0.1 ppm) filled with argon atmosphere by adopting 2032 type battery cases to obtain the lithium metal symmetrical battery, wherein the working electrode and the reference electrode are both lithium sheets, and the packaging pressure is 3MPa.

Test example 4

The electrolyte prepared in the comparative example 1, a working electrode and a reference electrode are assembled in a glove box (H ₂O≤0.1ppm,O₂ is less than or equal to 0.1 ppm) filled with argon atmosphere by adopting a 2032 type battery shell to obtain a lithium metal symmetrical battery, wherein the working electrode and the reference electrode are both lithium sheets, and the packaging pressure is 3MPa.

Test example 5

The electrolyte prepared in example 1, a working electrode and a reference electrode are assembled in a glove box (H ₂O≤0.1ppm,O₂ is less than or equal to 0.1 ppm) filled with argon atmosphere by adopting a 2032 type battery shell to obtain a lithium metal half-cell, the working electrode is a stainless steel sheet, the reference electrode is lithium metal, and the packaging pressure is 3MPa.

Test example 6

The electrolyte prepared in comparative example 1, a working electrode and a reference electrode are assembled in a glove box (H ₂O≤0.1ppm,O₂ is less than or equal to 0.1 ppm) filled with argon atmosphere by adopting a 2032 type battery shell to obtain a lithium metal half-cell, the working electrode is a stainless steel sheet, the reference electrode is lithium metal, and the packaging pressure is 3MPa.

The electrolytes of test examples 1 and 2 were subjected to fourier transform infrared spectroscopy (Fourier Transforminfrared spectroscopy, FTIR) and the results are shown in fig. 1, and it can be seen that VC and ICA were successfully copolymerized into a matrix in this example.

The results of the scanning electron microscope (Scanning Electron Microscope, SEM) morphology analysis of the electrolytes of test example 1 and test example 2 are shown in fig. 2 (a) and (b), respectively, and it is found that the electrolyte prepared in example 1 of the present application has smoother surface compared with comparative example 1, which is advantageous for improving physical contact with the electrode.

The electrolytes of test example 1 and test example 2 were subjected to C, F, B element energy dispersive X-ray Spectroscopy (EDS) analysis, and the results are shown in fig. 3 and 4, respectively, and it was found that the two elements C and F in the electrolytes prepared in example 1 and comparative example 1 of the present application were uniformly distributed, and the presence of the B element in example 1 indicates dissolution and uniform distribution of the lipfob salt.

The results of the analysis of the Li+ conductivity at 30-80 ℃ and the Li+ migration number at 10mV are shown in FIGS. 5 and 6, respectively, showing that the electrolyte prepared in example 1 of the present application has slightly lower conductivity than that of comparative example 1, but exhibits higher Li+ migration number at 30 ℃ and thus alleviates the concentration polarization phenomenon at the lithium anode interface.

The batteries prepared in test example 3 and test example 4 were subjected to EIS spectrum analysis, dynamic relaxation time distribution ((Dynamic Relaxation Time Distribution, DRT) cloud image analysis and activation energy analysis under 30-80 ℃ working conditions, respectively, and the results are shown in fig. 7-9 in sequence.

As can be seen from fig. 9, the activation energies of the batteries prepared in test example 3 and test example 4 were-0.7 eV and-0.79 eV, respectively, indicating that the electrolyte prepared in the examples of the present application has a lower li+ transport activation energy (0.7 eV).

As can be seen from fig. 7 and 8, the battery prepared in test example 3 has higher interfacial resistance than the battery prepared in test example 4, but the activation energy of li+ transport through the SEI is lower, indicating enhanced SEI stability.

The batteries prepared in test example 3 and test example 4 were subjected to critical current density tests, respectively, and the results showed that the critical current densities of the batteries prepared in test example 3 and test example 4 were 4.0mA/cm ²、3.5mA/cm², respectively, indicating that the electrolytes prepared in the examples of the present application had higher critical current densities.

The electrochemical window analysis of the cells prepared in test example 5 and test example 6 is shown in fig. 10, and it can be seen that the electrochemical windows of the cells prepared in test example 5 and test example 6 are 5.1V and 4.3V, respectively, which shows that the electrolyte prepared in the embodiment of the present application has a wider electrochemical stability window, and the good oxidation stability of the electrolyte is highlighted.

As can be seen from the above data, compared with the comparative example, the electrolyte prepared in the example of the present application has a higher critical current density (4.0 mA/cm ²), a wider electrochemical stability window (5.1V) and a lower li+ transport activation energy (0.7 eV), indicating that it has excellent stability to lithium metal and also has high voltage compatibility, and can maintain long-term stability of the interface structure of both lithium/electrolyte and electrolyte/anode.

The batteries prepared in test example 3 and test example 4 were subjected to cycle performance test and multiplying power performance test under conditions of 0.5mAcm ^-2 and 0.5mAh cm ^-2 respectively, and lithium negative electrode SEM images of the batteries after the batteries were cycled under conditions of 0.5mAcm ^-2 and 0.5mAh cm ^-2 were obtained, and the results are shown in FIGS. 11-13 respectively.

As can be seen from 11-13, the lithium-symmetric battery assembled in test example 3 can maintain stable overpotential under long cycle of 0.5mA cm ^-2、0.5mAh cm^-2 and 590h, which shows that the derived interface layer has good stability and can realize uniform and compact lithium metal deposition, while the lithium-symmetric battery assembled in test example 4 has rapid overpotential rising after 300h and can be attributed to dynamic degradation caused by interface degradation, and the recycled lithium metal presents obvious folds and protrusions, which proves the advantages of the electrolyte prepared by the embodiment of the application in regulating lithium deposition, and the lithium-symmetric battery assembled by the gel polymer electrolyte prepared by the application has more excellent cycle stability and rate capability.

The batteries assembled in example 1 and comparative example 1 were subjected to cycle performance test, rate performance test and cyclic voltammogram (Cyclic Voltammetry Curve, CV) test under 0.2C operating conditions, respectively, and the results are shown in fig. 14 to 16 in order.

As can be seen from 14 to 16, the battery prepared in example 1 can achieve a high coulombic efficiency of 99.75%, a capacity retention rate of 76.86% after 100 cycles at 0.2C, an initial specific capacity of 215.2mAh g ^-1 at 0.2C, and a reversible specific capacity of 156.4mAh g ^-1 at 1C, and can significantly improve the li+ diffusion coefficient of the positive electrode due to its excellent oxidation stability and interface contact characteristics, whereas comparative example 1 has a rapid capacity decay, a rapid rise in polarization voltage, and complete loss of electrochemical activity after 100 cycles despite a small initial interface impedance.

The batteries assembled in example 2 and example 3 were further tested for cycle performance under 0.2C operating conditions to compare and analyze the evolution of electrochemical performance of the batteries at different electrolyte composition ratios, and the related results are shown in fig. 17. It can be seen that the battery in example 2 exhibited a relatively low initial specific discharge capacity (169.0 mAh g ^-1) at 0.2C but had a higher capacity retention (51.4%) after 100 cycles, compared to example 3 (229.6 mAh g ^-1, 46.6%). This is due to the superior oxidation stability and interfacial compatibility induced by the higher ICA copolymer segment and the lipfob content in the electrolyte of example 2. Unfortunately, the decrease in ionic conductivity causes a decrease in its initial specific discharge capacity.

The above results demonstrate that the lithium metal solid-state battery assembled by the electrolyte prepared by the embodiment of the application shows more excellent cycle stability and rate capability and has high-voltage resistance.

In summary, in the electrolyte provided by the embodiment of the application, the monomers of the polymer matrix comprise ethylene carbonate and isocyanate ethyl acrylate, wherein the low HOMO energy level of the isocyanate ethyl acrylate can weaken the power-off capability of the polymer matrix, and improve the oxidation stability of the electrolyte, so that the poor electrochemical stability is improved, and the copolymerization structure of the ethylene carbonate and the isocyanate ethyl acrylate reduces the crystallinity of the polymer matrix, provides a smoother path for Li+ transmission, and further improves the ionic conductivity of the electrolyte. Therefore, the electrolyte provided by the application can effectively solve the problems of low ionic conductivity and poor electrochemical stability of the conventional electrolyte at room temperature, and has good application prospect.

Description of the terms

In the present application, a plurality means two or more.

The terms "first," "second," "third," "fourth," and the like in this disclosure, if any, are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order.

The term "and/or" in the present application is merely an association relation describing the association object, and indicates that three kinds of relations may exist, for example, a and/or B may indicate that a exists alone, while a and B exist together, and B exists alone. In the present application, the character "/" generally indicates that the front and rear related objects are an or relationship.

All steps of the present application may be performed sequentially or randomly unless otherwise specified. For example, the method comprises steps a and B, meaning that the method may comprise steps a and B performed sequentially, or may comprise steps B and a performed sequentially. For example, the method may further include step C, meaning that step C may be added to the method in any order, e.g., the method may include steps A, B and C, may include steps A, C and B, may include steps C, A and B, etc.

The foregoing description of the preferred embodiments of the application is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the application.

Claims

1. An electrolyte, characterized in that the electrolyte comprises a lithium salt, an organic solvent and a polymer matrix, wherein monomers of the polymer matrix comprise vinylene carbonate and ethyl isocyanate acrylate.

2. The electrolyte according to claim 1, wherein the lithium salt comprises lithium bis(trifluoromethanesulfonyl imide) and lithium difluorooxalatoborate, and the molar ratio of lithium bis(trifluoromethanesulfonyl imide) to lithium difluorooxalatoborate is (3-5):1.

3. The electrolyte according to claim 1, wherein the organic solvent comprises trimethyl phosphate and fluoroethylene carbonate, and the mass ratio of trimethyl phosphate to fluoroethylene carbonate is (2:3) to (3:2).

4. The electrolyte according to claim 1, wherein the electrolyte is a gel electrolyte, and further comprises a cross-linking agent and/or an initiator;

The cross-linking agent comprises at least one of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, ethoxylated trimethylolpropane triacrylate and methylene bisacrylamide;

The initiator includes at least one of azobisisobutyronitrile, dibenzoyl peroxide and azobisisoheptylnitrile.

5 . The electrolyte according to claim 1 , wherein the mass ratio of vinylene carbonate to ethyl isocyanate acrylate is (2:3) to (3:2).

6. The electrolyte according to claim 4, wherein the molar fraction of the crosslinking agent is 0.8 to 1.2% based on the total molar fraction of the monomers in the polymer matrix; and/or

Based on the total mass of monomers in the polymer matrix, the mass fraction of the initiator is 0.3-1%.

7. The electrolyte according to any one of claims 1 to 6, characterized in that the mass ratio of the monomer of the polymer matrix to the lithium salt is (3-10):1.

8. A battery, characterized in that the battery comprises a positive electrode sheet, a negative electrode sheet and the electrolyte according to any one of claims 1 to 7.

9. The battery according to claim 8, wherein the negative electrode plate comprises metallic lithium; and/or

The positive electrode active material of the positive electrode plate includes a lithium-rich manganese-based layered oxide.

10. An electrical device, characterized by comprising the battery according to claim 8 or 9, wherein the battery serves as a power supply for the electrical device.