Electrolyte, battery and electric equipment

Abstract

The embodiment of the invention provides an electrolyte, a battery and electric equipment, the electrolyte comprises a lithium salt, an organic solvent and a polymer matrix, and monomers of the polymer matrix comprise vinylene carbonate and isocyanate ethyl acrylate. In the electrolyte provided by the embodiment of the invention, the monomers of the polymer matrix comprise vinylene carbonate and isocyanate ethyl acrylate, and the low HOMO energy level of isocyanate ethyl acrylate can weaken the electron loss ability of the polymer matrix and improve the oxidation stability of the electrolyte, so that the relatively poor electrochemical stability is improved; and a copolymerization structure of vinylene carbonate and isocyanate ethyl acrylate reduces the crystallinity of a polymer matrix and provides a smoother path for Li < + > transmission, so that the ionic conductivity of the electrolyte is improved. Therefore, the electrolyte provided by the invention can effectively improve the problems of low room-temperature ionic conductivity and relatively poor electrochemical stability of the existing gel electrolyte, and has a good application prospect.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an electrolyte, a battery, and an electrical device. Background Art

[0002] Currently, gel electrolytes prepared by in-situ polymerization methods can effectively improve the physical contact between the electrode and electrolyte interface, reduce the interfacial impedance, and are compatible with existing lithium-ion battery manufacturing processes, making gel electrolytes one of the solid electrolyte materials with the greatest potential for scalability.

[0003] However, existing gel electrolytes still have problems such as low room temperature ionic conductivity, narrow electrochemical window and severe interfacial side reactions.

[0004] Based on this, there is an urgent need to develop an electrolyte that can simultaneously solve the problems of low room temperature ionic conductivity and poor electrochemical stability of gel electrolytes. Summary of the Invention

[0005] The embodiments of the present application provide an electrolyte, a battery, and an electrical device, aiming to improve the problems of low room temperature ionic conductivity and poor electrochemical stability of existing gel electrolytes.

[0006] In order to solve the above problems, this application is implemented through the following technical solutions:

[0007] The present application provides an electrolyte comprising a lithium salt, an organic solvent and a polymer matrix, wherein monomers of the polymer matrix comprise vinylene carbonate and ethyl isocyanate acrylate.

[0008] In the electrolyte provided in the embodiment of the present application, 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; while the copolymerization structure of vinylene carbonate and ethyl isocyanate acrylate reduces the crystallinity of the polymer matrix, which is Li + The transmission provides a smoother path, thereby improving the ionic conductivity of the electrolyte. Therefore, the electrolyte proposed in this application can effectively improve the low room temperature ionic conductivity and poor electrochemical stability of existing gel electrolytes, and has good application prospects.

[0009] Furthermore, in the electrolyte, the lithium salt includes lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalatoborate, and the molar ratio of lithium bis(trifluoromethanesulfonyl)imide to lithium difluorooxalatoborate is (3-5):1.

[0010] Furthermore, in the electrolyte, the organic solvent includes trimethyl phosphate and fluoroethylene carbonate, and the mass ratio of trimethyl phosphate to fluoroethylene carbonate is (2:3) to (3:2).

[0011] Furthermore, the electrolyte is a gel electrolyte, and the electrolyte further includes a cross-linking agent and / or an initiator;

[0012] The cross-linking agent comprises at least one of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, ethoxylated trimethylolpropane triacrylate and methylene bisacrylamide;

[0013] The initiator includes at least one of azobisisobutyronitrile, dibenzoyl peroxide and azobisisoheptylnitrile.

[0014] Furthermore, in the organic solvent, the mass ratio of trimethyl phosphate to fluoroethylene carbonate is (2:3) to (3:2).

[0015] Furthermore, the molar fraction of the crosslinking agent is 0.8 to 1.2% based on the total moles of monomers in the polymer matrix.

[0016] Furthermore, based on the total mass of monomers in the polymer matrix, the mass fraction of the initiator is 0.3-1%.

[0017] Furthermore, the mass ratio of the monomer of the polymer matrix to the lithium salt is (3-10):1.

[0018] The present application also proposes a battery, which includes a positive electrode sheet, a negative electrode sheet and the electrolyte as described above.

[0019] The negative electrode plate comprises metallic lithium; and / or

[0020] The positive electrode active material of the positive electrode plate includes a lithium-rich manganese-based layered oxide.

[0021] The present application also proposes an electrical device, comprising the battery as described above, wherein the battery serves as a power supply for the electrical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 : Fourier transform infrared spectra of the electrolytes in Test Example 1 and Test Example 2;

[0023] Figure 2 The scanning electron microscope morphology images of the electrolytes in Test Example 1 and Test Example 2;

[0024] Figure 3 This is the electrolyte energy dispersive X-ray spectrum in Test Example 1;

[0025] Figure 4 This is the electrolyte energy dispersive X-ray spectrum in Test Example 2;

[0026] Figure 5The Li+ conductivity analysis diagram of the electrolyte in Test Example 1 and Test Example 2;

[0027] Figure 6 The Li+ transference number analysis diagram of the electrolyte in Test Example 1 and Test Example 2;

[0028] Figure 7 The electrochemical impedance spectroscopy of the batteries in Test Example 3 and Test Example 4 is shown;

[0029] Figure 8 Dynamic relaxation time distribution cloud diagram of the battery in test example 3 and test example 4;

[0030] Figure 9 Activation energy analysis diagram of the battery in Test Example 3 and Test Example 4;

[0031] Figure 10 The electrochemical window analysis diagram of the electrolyte in Test Example 5 and Test Example 6;

[0032] Figure 11 The battery in test examples 3 and 4 is at 0.5 mA cm -2 and 0.5 mAh cm -2 Cyclic performance diagram under conditions;

[0033] Figure 12 The figure is the rate performance diagram of the battery in test example 3 and test example 4;

[0034] Figure 13 Scanning electron microscope images of the lithium negative electrode after battery cycling in Test Example 3 and Test Example 4;

[0035] Figure 14 Graph showing the cycle performance of the batteries in Example 1 and Comparative Example 1 under 0.2C operating conditions;

[0036] Figure 15 This is a graph of battery rate performance in Example 1 and Comparative Example 1;

[0037] Figure 16 The cyclic voltammetry curves of Example 1 and Comparative Example 1 are shown;

[0038] Figure 17 This is a cycle performance test of the batteries in Example 2 and Example 3 under 0.2C working conditions. DETAILED DESCRIPTION

[0039] In order to make the technical problems, technical solutions and beneficial effects solved by this application more clearly understood, this application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0040] Lithium-ion batteries (LIBs) typically utilize a graphite anode, a layered oxide cathode, and an organic liquid electrolyte. These batteries struggle to overcome low energy density (<300Wh / kg) and the risk of thermal runaway, failing to meet the demands for safe and efficient energy storage devices in the electronics and automotive industries. While the combination of a lithium metal anode (theoretical capacity 3860mAh / g) and a solid-state electrolyte is considered a core technology for next-generation batteries, its development is hampered by issues such as lithium dendrite growth and an unstable electrolyte / electrode interface.

[0041] The applicant has found that the use of high modulus, non-flammable solid electrolytes instead of flammable organic liquid electrolytes has been proven to be able to effectively overcome the limitations of lithium metal negative electrodes and significantly improve battery safety, making solid-state lithium metal batteries a very promising solution in advanced battery technology. Among them, the electrolyte prepared by the in-situ polymerization method can effectively improve the physical contact between the electrode and the electrolyte interface, reduce the interfacial impedance, and is compatible with the existing lithium-ion battery manufacturing process, making the electrolyte one of the solid electrolyte materials with the greatest potential for scalability. However, existing electrolytes still have problems such as low room temperature ionic conductivity, narrow electrochemical window, and serious interfacial side reactions.

[0042] Therefore, developing a gel polymer electrolyte that can efficiently accommodate lithium metal negative electrodes and high-voltage positive electrode materials while having good ion transport properties is of positive significance for promoting the development of solid-state lithium metal batteries and polymer solid electrolytes.

[0043] Based on the above findings, in order to solve the problems of low room temperature ionic conductivity and poor electrochemical stability of the above electrolyte, the embodiment of the present application provides an electrolyte, including a lithium salt, an organic solvent and a polymer matrix, wherein the monomers of the polymer matrix include vinylene carbonate (VC) and isocyanate ethyl acrylate (ICA). In the electrolyte provided by the embodiment of the present application, the HOMO (highest occupied molecular orbital) energy level of isocyanate ethyl acrylate as low as -7.68eV 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 isocyanate ethyl acrylate reduces the crystallinity of the polymer matrix, which is Li + The transmission provides a smoother path, thereby improving the ionic conductivity of the electrolyte. Therefore, the electrolyte proposed in this application can effectively improve the low room temperature ionic conductivity and poor electrochemical stability of existing gel electrolytes, and has good application prospects.

[0044] In one embodiment, infrared testing can be used to detect that the electrolyte of the battery includes components such as vinylene carbonate and isocyanate ethyl acrylate.

[0045] Alternatively, in one embodiment, in the electrolyte provided in the embodiments of the present application, the mass ratio of vinylene carbonate to ethyl isocyanate acrylate is (2:3) to (3:2), which can achieve a balance between the high-voltage stability of the electrolyte and the ionic conductivity. In some embodiments, the mass ratio of vinylene carbonate to ethyl isocyanate acrylate can be in the range of one or both of 3:2, 3:3, and 2:3.

[0046] In the electrolyte provided by the embodiment of the present invention, the above-mentioned lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium perchlorate, and lithium trifluoromethanesulfonate, which can be adapted to the above-mentioned polymer matrix to form an interface film rich in lithium nitrogen compounds that is conducive to ion conduction.

[0047] Alternatively, in one embodiment, the lithium salt includes lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluorooxalatoborate (LiDFOB).

[0048] In this embodiment, lithium bis(trifluoromethanesulfonyl imide) and lithium difluorooxalatoborate are used as lithium salts. The narrow LUMO-HOMO (lowest unoccupied molecular orbital-highest occupied molecular orbital) energy gap of lithium difluorooxalatoborate, which is as narrow as 5.13 eV, can promote its preferential decomposition on the electrode surface to form inorganic components rich in BO and BF, optimize the Li+ transmission path, and form a dense and stable interfacial layer. As a result, the electrolyte forms an inorganic-rich, dense and stable solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) on the surface of the lithium metal negative electrode and the lithium-rich manganese-based layered oxide positive electrode, which not only promotes the uniform deposition of lithium and inhibits dendrite growth, but also greatly reduces interfacial side reactions, so that the assembled solid-state lithium metal battery exhibits excellent high-voltage cycle stability and interfacial dynamics.

[0049] Alternatively, in one embodiment, in the electrolyte provided in the embodiments of the present application, the molar ratio of lithium bis(trifluoromethanesulfonyl imide) to lithium difluorooxalatoborate as lithium salts is (3-5):1. This molar ratio results in a moderate thickness of the electrode / electrolyte interface phase and good interfacial stability. In some embodiments, the molar ratio of lithium bis(trifluoromethanesulfonyl imide) to lithium difluorooxalatoborate can be in the range of one or both of 3:1, 4:1, and 5:1.

[0050] 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 take into account excellent ionic conductivity, high-voltage cycle stability and interface dynamics.

[0051] In some embodiments, the mass ratio of the monomer of the polymer matrix to the lithium salt can be 3 : 1, 5 : 1, 10 : 1 or any two range values.

[0052] Optionally, in the electrolyte of the secondary battery provided by an embodiment of the present invention, the concentration of the lithium salt is 0.5 to 2 mol / L, for example, one or both of 0.5 mol / L, 1 mol / L, 1.5 mol / L, and 2 mol / L. A lithium salt concentration within this range not only effectively constructs a solid electrolyte interface primarily composed of inorganic components, but also avoids the problem of decreased ionic conductivity due to increased electrolyte viscosity.

[0053] Alternatively, in one embodiment, the organic solvent includes trimethyl phosphate and fluoroethylene carbonate.

[0054] In this embodiment, trimethyl phosphate (TMP) and fluoroethylene carbonate (FEC) are used as solvents in the electrolyte. The introduction of fluoroethylene carbonate can further increase the content of LiF in the SEI on the surface of the lithium metal negative electrode, reduce the Li+ diffusion barrier, and make the room temperature ionic conductivity of the electrolyte reach 0.12mS cm -1 , the Li+ migration number is increased to 0.435, which effectively alleviates the concentration polarization phenomenon, enhances the interface mechanical strength and ion transmission capacity, and the entry of trimethyl phosphate can improve the flame retardancy and ion transmission performance of the electrolyte.

[0055] Alternatively, in one embodiment, the mass ratio of trimethyl phosphate and fluoroethylene carbonate as organic solvents is (2:3) to (3:2), and the resulting electrolyte can have good flame retardancy, ion transport properties, and good lithium stability. In some embodiments, the mass ratio of trimethyl phosphate and fluoroethylene carbonate can be in the range of one or both of 3:2, 3:3, and 3:2.

[0056] Optionally, in one embodiment, the electrolyte further includes a crosslinking agent, and 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 methylene bisacrylamide (MBA);

[0057] In this embodiment, the cross-linking agent is introduced into the electrolyte, which can efficiently cross-link with the double bonds in vinylene carbonate and ethyl isocyanate acrylate to form a stable three-dimensional interconnected network, thereby improving the mechanical strength of the electrolyte.

[0058] Optionally, in some embodiments, the cross-linking agent is polyethylene glycol diacrylate (PEGDA). The polyethylene glycol diacrylate segment contains two acrylate groups at the end, which can efficiently cross-link with the double bonds in vinylene carbonate and isocyanate ethyl acrylate monomers to form a stable three-dimensional interconnected network, thereby improving the mechanical strength of the electrolyte. At the same time, the polyethylene glycol segment (-CH2CH2O-) in the polyethylene glycol diacrylate can give the electrolyte good flexibility, which is conducive to good interface contact between the electrolyte and the electrode material. In addition, polyethylene glycol diacrylate has good compatibility with monomers such as vinylene carbonate and isocyanate ethyl acrylate and solvents such as trimethyl phosphate and fluoroethylene carbonate, which helps to evenly distribute the polyethylene glycol diacrylate in the electrolyte slurry and improve the uniformity of the electrolyte component structure.

[0059] The electrolyte provided in the embodiments of the present application may be a gel electrolyte. Optionally, in one embodiment, the electrolyte further includes an initiator, wherein the initiator includes at least one of azobisisobutyronitrile (AIBN), dibenzoyl peroxide (BPO), and azobisisoheptanenitrile (ABVN).

[0060] In this embodiment, the initiator can be cleaved at a relatively low temperature of 60 to 80° C. to generate free radical active centers, and promote the chain polymerization reaction of vinylene carbonate and isocyanate ethyl acrylate, with a high initiation efficiency.

[0061] Optionally, in one embodiment, 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, which can effectively balance the mechanical strength of the electrolyte and its interface contact with the electrode, and inhibit the growth of lithium dendrites.

[0062] In some embodiments, the molar fraction of the crosslinking agent, based on the total moles of monomers in the polymer matrix, may be in the range of 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, or any two thereof.

[0063] Optionally, in some embodiments, the initiator is azobisisobutyronitrile (AIBN), which can not only generate free radical active centers by cleavage at a relatively low temperature of 60 to 80°C, but also promote chain polymerization of vinylene carbonate and isocyanate ethyl acrylate, with a high initiation efficiency; in addition, the decomposition products of azobisisobutyronitrile are nitrogen and a small amount of low-toxic isobutyronitrile, which have little effect on the chemical stability of the electrolyte system (such as lithium salts, solvents), thereby avoiding the introduction of harmful impurities.

[0064] Optionally, in some embodiments, the mass fraction of the above-mentioned initiator is 0.3-1% based on the total mass of the monomers of the polymer matrix, which can not only provide sufficient free radicals to avoid residual unpolymerized monomers and reduce the mechanical strength and chemical stability of the electrolyte, but also avoid the initiator or its by-products remaining in the electrolyte, triggering interfacial side reactions and worsening the battery cycle stability.

[0065] In some embodiments, the mass fraction of the initiator is in the range of 0.3%, 0.5%, 1.0%, or any two of the above, based on the total molar fraction of the monomers in the polymer matrix.

[0066] In a specific embodiment, the electrolyte provided in the examples of the present application uses a copolymer of VC and ICA as monomers, LiTFSI and LiDFOB as lithium salts, PEGDA as a cross-linking agent, and AIBN as an initiator.

[0067] In the embodiments of the present application, a two-component synergistic modulation strategy is adopted to synergistically optimize the polymer matrix of the electrolyte and the electrolyte components, broaden the electrochemical window of the electrolyte and improve the electrolyte / electrode interface compatibility, and promote the steady improvement of the cycle stability and rate performance of the solid-state lithium metal battery.

[0068] Among them, the low HOMO energy level of isocyanate ethyl acrylate can weaken the electron loss ability of the polymer matrix and improve the oxidative stability of the electrolyte; the narrow LUMO-HOMO energy gap of lithium difluorooxalatoborate can promote its preferential decomposition on the electrode surface, forming a dense and stable interface layer. At the same time, the introduction of fluoroethylene carbonate further increases the content of LiF in the SEI on the surface of the lithium metal negative electrode, enhancing the mechanical strength of the interface and the ion transport capacity. In addition, the copolymerization structure of vinylene carbonate and isocyanate ethyl acrylate reduces the crystallinity of the polymer matrix, which is a good choice for Li metal anode. + The electrolyte provides a smoother path for transport. Thanks to this, the electrolyte forms dense and stable SEI and CEI layers rich in inorganic components on the surface of the lithium metal negative electrode and the 4.6V LRMO (lithium-rich manganese-based positive electrode material). This not only promotes the uniform deposition of lithium and inhibits dendrite growth, but also significantly reduces interfacial side reactions, making the assembled solid-state lithium metal battery exhibit excellent high-voltage cycling stability and interfacial dynamics.

[0069] The electrolyte provided in the embodiments of the present application can construct a stable interfacial layer in situ on the surface of the lithium metal negative electrode and the LRMO positive electrode; wherein, the decomposition products of LiDFOB (BO, BF) and FEC-derived LiF together form SEI and CEI layers with high mechanical strength and ionic conductivity, effectively suppressing lithium dendrite growth and interfacial side reactions.

[0070] The electrolyte provided in the embodiments of the present application has excellent high-voltage stability and an electrochemical window of more than 5.1V (vs. Li + / Li), meeting the application requirements of 4.6V-class LRMO cathodes. The copolymerization design of vinylene carbonate and ethyl isocyanate acrylate reduces the electronic activity of the polymer matrix and inhibits oxidative decomposition under high voltage. At the same time, the synergistic effect of LiDFOB and FEC forms a CEI layer rich in BO, BF, and LiF at the cathode interface, significantly reducing electrolyte side reactions and ensuring long-term cycling stability under high voltage. Solid-state lithium batteries based on this electrolyte can still maintain 99.75% of the initial coulombic efficiency and 76.8% capacity retention after 100 cycles at a high voltage of 4.6V.

[0071] In addition, the electrolyte provided in the embodiments of the present application can be prepared using an in-situ thermal polymerization process, with a polymerization temperature of only 70°C, a simple process with low energy consumption. In addition, the cost of the electrolyte raw materials is controllable, and it has the potential for large-scale production.

[0072] The present invention provides a method for preparing an electrolyte. Figure 1 As shown, the method includes steps 101 to 103:

[0073] Step 101: Mixing monomers of a polymer matrix with a cross-linking agent to obtain a first slurry; wherein the monomers of the polymer matrix include vinylene carbonate and ethyl isocyanate acrylate;

[0074] Step 102: mixing a lithium salt with an organic solvent to obtain a second slurry;

[0075] Step 103: Mix the first slurry and the second slurry, and then add an initiator to obtain an electrolyte.

[0076] In the embodiment of the present application, an in-situ thermal polymerization process is adopted to prepare the electrolyte as described above through steps 101 to 203; wherein, vinylene carbonate and ethyl isocyanate acrylate are used as polymer monomers, and the low HOMO energy level of ethyl isocyanate acrylate can weaken the electron loss ability of the polymer matrix, improve the oxidation 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, which is Li + The transport provides a smoother path, thereby improving the ionic conductivity of the electrolyte.

[0077] Therefore, the electrolyte prepared in this application can effectively improve the problems of low room temperature ionic conductivity and poor electrochemical stability of existing electrolytes, and has good application prospects.

[0078] In addition, in the above preparation process, the polymerization temperature is as low as 70°C, the process is simple and the energy consumption is low, and the cost of electrolyte raw materials is controllable, which is suitable for large-scale production.

[0079] Alternatively, in one embodiment, in the above step 101, after adding the crosslinking agent to the monomer of the polymer matrix, the mixture can be mixed by stirring or the like, and the stirring time can be one of or any two of 1 hour, 2 hours, 6 hours, and 12 hours; wherein, the mass ratio of vinylene carbonate and ethyl isocyanate acrylate is (2:3) to (3:2), which can achieve a balance between the high-voltage stability of the electrolyte and the ionic conductivity. In some embodiments, the mass ratio of vinylene carbonate and ethyl isocyanate acrylate can be one of or any two of 3:2, 3:3, and 3:2.

[0080] Optionally, in step 101, the cross-linking 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);

[0081] The amount of the cross-linking agent added is 0.8-1.2% of the total molar amount of the monomers of the polymer, which can balance the mechanical strength of the electrolyte and the interface contact between the electrolyte and the electrode, and inhibit the growth of lithium dendrites.

[0082] Optionally, the cross-linking agent may be polyethylene glycol diacrylate (PEGDA). Since PEGDA does not undergo thermal decomposition within the thermal polymerization temperature (70° C.), the PEGDA content in the product is still maintained at 0.8 to 1.2 mol % of the monomer of the polymer.

[0083] In the preparation method provided in an embodiment of the present invention, in the above-mentioned step 102, after the lithium salt is added to the organic solvent, it can be mixed by stirring or the like, and the stirring time can be one or two of the range values ​​of 1h, 2h, 6h, 12h; wherein the lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium perchlorate, and lithium trifluoromethanesulfonate, which can be adapted to the above-mentioned polymer matrix to form an interface film rich in lithium nitrogen compounds that is conducive to ion conduction.

[0084] Optionally, in one embodiment, in the step 102, the lithium salt includes lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluorooxalatoborate (LiDFOB).

[0085] Alternatively, in one embodiment, in step 102, the molar ratio of lithium bis(trifluoromethanesulfonylimide) to lithium difluorooxalatoborate as the lithium salt is (3-5):1. This molar ratio results in an electrode / electrolyte interface with a moderate thickness and good interfacial stability. In some embodiments, the molar ratio of lithium bis(trifluoromethanesulfonylimide) to lithium difluorooxalatoborate can be within the range of 3:1, 4:1, 5:1, or any two of these.

[0086] Optionally, in one embodiment, in the above step 102, the mass ratio of the monomer of the polymer matrix to the above lithium salt is controlled to be (3-10):1, so that the electrolyte can effectively take into account excellent ionic conductivity, high-voltage cycle stability and interface dynamics.

[0087] Optionally, in one embodiment, in step 102, the concentration of the lithium salt is controlled to be 0.5 to 2 mol / L, for example, in the range of 0.5 mol / L, 1 mol / L, 1.5 mol / L, or 2 mol / L, or any two thereof. A lithium salt concentration within the above range not only effectively constructs a solid electrolyte interface composed primarily of inorganic components, but also avoids the problem of decreased ionic conductivity due to increased electrolyte viscosity.

[0088] Optionally, in 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) to (3:2). The resulting electrolyte can have good flame retardancy, ion transport properties, and good lithium stability. In some embodiments, the mass ratio of trimethyl phosphate to fluoroethylene carbonate can be in the range of 3:2, 3:3, 3:2, or any two of them.

[0089] Optionally, in step 103, the initiator includes at least one of azobisisobutyronitrile (AIBN), dibenzoyl peroxide (BPO) and azobisisoheptanenitrile (ABVN).

[0090] In this embodiment, the initiator can be cleaved at a relatively low temperature of 60 to 80° C. to generate free radical active centers, and promote the chain polymerization reaction of vinylene carbonate and isocyanate ethyl acrylate, with a high initiation efficiency.

[0091] Optionally, in one embodiment, in the above-mentioned step 103, the amount of the above-mentioned initiator added is 0.3 to 1% of the total mass of the monomers of the polymer matrix, which can not only provide sufficient free radicals to avoid residual unpolymerized monomers and reduce the mechanical strength and chemical stability of the electrolyte, but also avoid the initiator or its by-products remaining in the electrolyte, triggering interfacial side reactions and worsening the battery cycle stability.

[0092] Optionally, in some embodiments, the initiator is azobisisobutyronitrile (AIBN), which can not only generate free radical active centers by cleavage at a relatively low temperature of 60 to 80°C, but also promote chain polymerization of vinylene carbonate and isocyanate ethyl acrylate, with a high initiation efficiency; in addition, the decomposition products of azobisisobutyronitrile are nitrogen and a small amount of low-toxic isobutyronitrile, which have little effect on the chemical stability of the electrolyte system (such as lithium salts, solvents), thereby avoiding the introduction of harmful impurities.

[0093] An embodiment of the present application also provides a battery, comprising a positive electrode sheet, a negative electrode sheet and the electrolyte as described above.

[0094] 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 includes at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate.

[0095] Optionally, in one embodiment, the positive electrode active material includes lithium-rich manganese-based layered oxide (LRMO), which can not only give full play to the higher theoretical specific capacity (>300mAh g -1 ) and a higher operating voltage limit (~4.8V). The above electrolyte can also be used to in situ construct an inorganic-rich, dense and stable CEI layer on the surface of the 4.6V LRMO cathode, which not only promotes the uniform deposition of lithium and inhibits dendrite growth, but also greatly reduces interfacial side reactions, making the assembled solid-state lithium metal battery exhibit excellent high-voltage cycling stability and interfacial dynamics.

[0096] Symmetrical battery tests show that the electrolyte can achieve a critical current density of lithium deposition of 4.0 mA cm -2 , and at 0.5 mA cm -2 It achieves stable cycling for more than 500 hours with an activation energy as low as 0.70 eV, which is significantly better than traditional polymer electrolytes.

[0097] In the battery provided in the embodiment of the present application, the positive electrode plate also includes a conductive agent and a binder; optionally, the conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene, and the binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0098] In some embodiments, the positive electrode sheet is prepared as follows: the components for preparing the positive electrode sheet, such as the positive electrode material, the adhesive and any other components, are dispersed in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; the positive electrode slurry is coated on both sides of a positive electrode current collector such as aluminum foil; and after baking, rolling, cutting, striping and other processes, the positive electrode sheet can be obtained.

[0099] The secondary battery provided by the embodiment of the present invention further includes a separator.

[0100] In some embodiments, the negative electrode plate is a metal lithium plate.

[0101] The lithium metal negative electrode has a capacity of 3860mAh g -1 The high theoretical specific capacity and low electrode potential of -3.04V (vs.SHE) can maximize the energy density of the battery system; at the same time, the above-mentioned electrolyte is used to in situ construct an inorganic-rich, dense and stable SEI on the surface of the lithium metal negative electrode, which not only promotes the uniform deposition of lithium and inhibits dendrite growth, but also greatly reduces interfacial side reactions, so that the assembled solid-state lithium metal battery exhibits excellent high-voltage cycle stability and interfacial dynamics.

[0102] In other embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The above-mentioned negative electrode active material layer can adopt negative electrode active materials used for batteries, and the negative electrode active materials include any one of hard carbon, soft carbon, graphite, and silicon oxide, or a combination of at least two of them.

[0103] In the case where the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode sheet is prepared as follows: the components for preparing the negative electrode sheet, such as the negative electrode active material, the binder, and the conductive agent, are dispersed in a solvent such as deionized water to form a negative electrode slurry; the negative electrode slurry is coated on both sides of a negative electrode current collector such as copper foil; and after processes such as baking, rolling, cutting, and slitting, the negative electrode sheet can be obtained.

[0104] In practical applications, the negative electrode sheet, separator and positive electrode sheet are stacked in order and wound to obtain a core, which is then packaged to obtain a bare cell. The bare cell is baked and then injected, formed, sealed and sorted to obtain the above-mentioned secondary battery.

[0105] The present invention also provides an electrical device, which includes the above-mentioned battery, and the battery serves as a power supply for the electrical device.

[0106] For the above-mentioned electrical equipment embodiment, it includes the above-mentioned battery and can achieve the same technical effect. In order to avoid repetition, it will not be described here. For relevant matters, please refer to the partial description of the battery embodiment.

[0107] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention is further described below in conjunction with examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0108] The present invention is described in detail below by way of examples.

[0109] Example 1

[0110] (1) Electrolyte preparation

[0111] S1, mixing polymer monomers VC and ICA in a mass ratio of 1:1, adding PEGDA with a monomer concentration of 1 mol%, and stirring to obtain a first slurry;

[0112] S2, uniformly mixing 0.8M LiTFSI, 0.2M LiDFOB and TMP / FEC (1:1 wt%) solvent, and stirring to obtain a second slurry;

[0113] S3, mixing the first slurry and the second slurry in a mass ratio of 1:1, adding 0.5 wt% of the monomer mass of AIBN initiator after stirring, and thermally polymerizing at 70° C. for 2 h to obtain an electrolyte;

[0114] (2) Preparation of positive electrode sheet

[0115] The above-mentioned positive electrode material, lithium manganese oxide, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed uniformly in a mass ratio of 8:1:1, and NMP solvent was added and stirred under vacuum conditions to mix uniformly. The above slurry was coated on both sides of 14μm carbon-coated aluminum foil, and the surface loading was controlled to be 2.5mg / cm 2 , and then placed in an oven to dry at a high temperature of 110°C, and then through processes such as rolling, cutting, and slitting to prepare the positive electrode sheet.

[0116] (3) Preparation of negative electrode sheet

[0117] Metal lithium sheet is selected as the negative electrode.

[0118] (4) Preparation of batteries

[0119] In a glove box where the argon and water oxygen values ​​are both <1 ppm, the positive electrode sheet prepared by step (2), the negative electrode sheet prepared by step (3) and the electrolyte prepared by step (1) are assembled into a lithium metal full battery using a 2032 type battery shell, and the packaging pressure is 3 MPa.

[0120] Example 2

[0121] The difference between Example 2 and Example 1 is that:

[0122] In step S1, the mass ratio of VC to ICA was adjusted to 2:3, and the amount of PEGDA added was adjusted to a monomer concentration of 0.8 mol%;

[0123] In step S2, the amount of LiTFSI added was adjusted to 0.6 M and the mass ratio of TMP / FEC was adjusted to 2:3;

[0124] In step S3, the amount of AIBN initiator added is adjusted to 0.3 wt% of the monomer mass.

[0125] Example 3

[0126] The difference between Example 3 and Example 1 is that:

[0127] In step S1, the mass ratio of VC to ICA was adjusted to 3:2, and the amount of PEGDA added was adjusted to a monomer concentration of 1.2 mol%;

[0128] In step S2, the amount of LiTFSI added was adjusted to 1.0 M and the mass ratio of TMP / FEC was adjusted to 3:2;

[0129] In step S3, the amount of AIBN initiator added is adjusted to 1.0 wt% of the monomer mass.

[0130] Comparative Example 1

[0131] The difference between Comparative Example 1 and Example 1 is that in step S1, ICA monomer is not added, and in step S2, LiDFOB salt and FEC solvent are not added.

[0132] Test Example 1

[0133] The electrolyte prepared in Example 1, the working electrode, and the reference electrode were assembled in a glove box filled with argon atmosphere (H2O≤0.1ppm, O2≤0.1ppm) using a 2032 type battery shell to obtain a stainless steel symmetrical battery. The working electrode and the reference electrode were both stainless steel sheets, and the packaging pressure was 3MPa.

[0134] Test Example 2

[0135] The electrolyte prepared in Comparative Example 1 was assembled with the working electrode and the reference electrode in a glove box filled with argon atmosphere (H2O≤0.1ppm, O2≤0.1ppm) using a 2032 type battery shell to obtain a stainless steel symmetrical battery. The working electrode and the reference electrode were both stainless steel sheets, and the packaging pressure was 3MPa.

[0136] Test Example 3

[0137] The electrolyte prepared in Example 1 was assembled with the working electrode and the reference electrode in a glove box filled with argon atmosphere (H2O≤0.1ppm, O2≤0.1ppm) using a 2032 type battery shell to obtain a lithium metal symmetrical battery. The working electrode and the reference electrode were both lithium sheets, and the packaging pressure was 3MPa.

[0138] Test Example 4

[0139] The electrolyte prepared in Comparative Example 1 was assembled with the working electrode and the reference electrode in a glove box filled with argon atmosphere (H2O≤0.1ppm, O2≤0.1ppm) using a 2032 type battery shell to obtain a lithium metal symmetrical battery. The working electrode and the reference electrode were both lithium sheets, and the packaging pressure was 3MPa.

[0140] Test Example 5

[0141] The electrolyte prepared in Example 1 was assembled with the working electrode and the reference electrode in a glove box filled with argon atmosphere (H2O≤0.1ppm, O2≤0.1ppm) using a 2032 type battery shell to obtain a lithium metal half-cell. The working electrode was a stainless steel sheet, and the reference electrode was lithium metal. The packaging pressure was 3MPa.

[0142] Test Example 6

[0143] The electrolyte prepared in Comparative Example 1 was assembled with the working electrode and the reference electrode in a glove box filled with argon atmosphere (H2O≤0.1ppm, O2≤0.1ppm) using a 2032 type battery shell to obtain a lithium metal half-cell. The working electrode was a stainless steel sheet, the reference electrode was lithium metal, and the packaging pressure was 3MPa.

[0144] The electrolytes in Test Example 1 and Test Example 2 were analyzed by Fourier Transform Infrared Spectroscopy (FTIR). The results are as follows: Figure 1 As shown, it can be seen that VC and ICA in this embodiment are successfully copolymerized into a matrix.

[0145] The electrolytes in Test Example 1 and Test Example 2 were subjected to scanning electron microscope (SEM) morphology analysis, and the results were as follows: Figure 2 As shown in (a) and (b), it can be seen that compared with Comparative Example 1, the surface of the electrolyte prepared in Example 1 of the present application is smoother, which is conducive to improving the physical contact with the electrode.

[0146] The electrolytes in Test Example 1 and Test Example 2 were subjected to Energy Dispersive X-ray Spectroscopy (EDS) analysis of C, F, and B elements. The results were as follows: Figure 3 、 4 As shown, it can be seen that the C and F elements are evenly distributed in the electrolytes prepared in Example 1 and Comparative Example 1 of the present application, and the presence of the B element in Example 1 indicates the dissolution and even distribution of the LiDFOB salt.

[0147] The electrolytes in Test Example 1 and Test Example 2 were subjected to Li+ conductivity analysis at 30°C-80°C working conditions and Li+ transference number analysis at 10mV working conditions. The results are as follows: Figure 5 、 6 As shown, it can be seen that the conductivity of the electrolyte prepared in Example 1 of the present application is slightly lower than that in Comparative Example 1, but it shows a higher Li+ migration number at 30°C, which alleviates the concentration polarization phenomenon at the lithium negative electrode interface.

[0148] The batteries prepared in Test Example 3 and Test Example 4 were subjected to EIS spectrum analysis, dynamic relaxation time distribution (DRT) cloud analysis under 30-80°C working conditions, and activation energy analysis, respectively. The results are as follows: Figures 7-9 shown.

[0149] Depend on Figure 9 It can be seen that the activation energies of the batteries prepared in Test Example 3 and Test Example 4 are -0.7 eV and -0.79 eV, respectively, indicating that the electrolyte prepared in the embodiment of the present application has a lower Li+ transport activation energy (0.7 eV).

[0150] Depend on Figure 7 、 8 It can be seen that the battery prepared in Test Example 3 has a higher interfacial resistance than the battery prepared in Test Example 4, but the activation energy of Li+ transmission through SEI is lower, indicating that the SEI stability is enhanced.

[0151] The critical current density of the batteries prepared in Test Example 3 and Test Example 4 was tested respectively. The results showed that the critical current density of the batteries prepared in Test Example 3 and Test Example 4 was 4.0 mA / cm 2 , 3.5mA / cm 2 , indicating that the electrolyte prepared in the embodiment of the present application has a higher critical current density.

[0152] The batteries prepared in Test Example 5 and Test Example 6 were subjected to electrochemical window analysis, and the results were as follows: Figure 10As shown, it can be seen that the electrochemical windows of the batteries prepared in Test Example 5 and Test Example 6 are 5.1 V and 4.3 V, respectively, indicating that the electrolyte prepared in the embodiment of the present application has a wider electrochemical stability window, highlighting the good oxidation stability of the electrolyte.

[0153] From the above data, it can be seen that compared with the comparative example, the electrolyte prepared in the embodiment 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+ transfer activation energy (0.7eV), indicating its excellent stability to lithium metal and high voltage compatibility, and its ability to maintain the long-term stability of the interface structures of lithium / electrolyte and electrolyte / positive electrode.

[0154] The batteries prepared in Test Example 3 and Test Example 4 were respectively -2 and 0.5 mAh cm -2 The cycle performance test and rate performance test were carried out under the conditions and the battery was tested at 0.5 mA cm -2 and 0.5 mAh cm -2 The SEM images of the lithium negative electrode after cycling under the conditions are as follows: Figures 11-13 shown.

[0155] As shown in Figures 11 to 13, the lithium symmetrical battery assembled in Test Example 3 can -2 , 0.5mAh cm -2 , and maintain a stable overpotential under long cycles of 590h, indicating that its derived interface layer has good stability and can achieve uniform and dense lithium metal deposition; while the lithium symmetrical battery assembled in Test Example 4 has a rapid increase in overpotential after 300h, which can be attributed to the kinetic decay caused by interface degradation, and the lithium metal after the cycle shows obvious wrinkles and protrusions; this confirms the advantages of the electrolyte prepared in the examples of the present application in regulating lithium deposition, and the lithium symmetrical battery assembled using the gel polymer electrolyte prepared by the present invention exhibits more excellent cycle stability and rate performance.

[0156] The batteries assembled in Example 1 and Comparative Example 1 were subjected to cycle performance test, rate performance test and cyclic voltammetry curve (CV) test under 0.2C working condition, and the results are as follows: Figures 14-16 shown.

[0157] As shown in Figures 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, and an initial specific capacity of 215.2 mAh g at 0.2C. -1The reversible specific capacity at 1C is maintained at 156.4 mAh g -1 , which can significantly improve the Li+ diffusion coefficient of the positive electrode, which is attributed to its excellent oxidation stability and interface contact characteristics; while in Comparative Example 1, although the initial interface impedance is small, its capacity decays rapidly, the polarization voltage rises rapidly, and it completely loses its electrochemical activity after 100 cycles.

[0158] The cycling performance of the batteries assembled in Example 2 and Example 3 under 0.2C working conditions was further tested to compare and analyze the evolution of the electrochemical performance of the batteries under different electrolyte composition ratios. The relevant results are as follows: Figure 17 As shown. It can be seen that compared with Example 3 (229.6 mAh g -1 , 46.6%), although the battery in Example 2 exhibited a relatively low initial discharge specific capacity (169.0 mAh g -1 ), but with a higher capacity retention (51.4%) after 100 cycles. This is attributed to the excellent oxidative stability and interfacial compatibility induced by the higher ICA copolymer segment and LiDFOB content in the electrolyte of Example 2. Unfortunately, the reduction in ionic conductivity resulted in a decrease in the initial discharge specific capacity.

[0159] The above results show that the lithium metal solid-state battery assembled using the electrolyte prepared in the embodiment of the present application exhibits better cycle stability and rate performance, and has high-voltage resistance.

[0160] In summary, 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 this application can effectively improve the problems of low room temperature ionic conductivity and poor electrochemical stability of existing electrolytes, and has good application prospects.

[0161] Terminology

[0162] In this application, a plurality refers to two or more.

[0163] The terms "first," "second," "third," "fourth," etc. (if any) in this application are used to distinguish similar objects and are not necessarily used to describe a particular sequential order.

[0164] The term "and / or" in this application simply describes an association between related objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this application generally indicates that the related objects are in an "or" relationship.

[0165] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly. For example, a statement that the method includes steps A and B indicates that the method may include steps A and B performed sequentially, or steps B and A performed sequentially. For example, a statement that the method may also include step C indicates that step C may be added to the method in any order, for example, the method may include steps A, B, and C, or steps A, C, and B, or steps C, A, and B, etc.

[0166] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

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

2. The electrolyte according to claim 1, characterized in that The lithium salt includes 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, characterized in that The organic solvent includes 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, characterized in that 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 methylene bisacrylamide; The initiator includes at least one of azobisisobutyronitrile, dibenzoyl peroxide and azobisisoheptylnitrile.

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

6. The electrolyte according to claim 4, characterized in that 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, characterized in that 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 in that: The device comprises a battery as described in claim 8 or 9, wherein the battery serves as a power supply for the electrical device.

Images