An electrochemical device and a gel electrolyte

Abstract

The application relates to an electrochemical device and a gel electrolyte. The electrochemical device comprises a gel electrolyte, a positive electrode sheet and a negative electrode sheet, wherein the gel electrolyte comprises an acrylate polymer, a sulfur-containing additive and a lithium salt additive, the mass fraction of the acrylate polymer in the gel electrolyte is a, the mass fraction of the sulfur-containing additive is b, and the mass fraction of the lithium salt additive is c, and a, b and c satisfy: 0.5 <= a / (b+c) < 10. The electrochemical device can balance low internal resistance, high cycle performance and high safety performance.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to an electrochemical device and a gel electrolyte. Background Technology

[0002] Electric vehicles have seen significant development in recent years as a crucial means of achieving global carbon emission reduction. Electrochemical devices, as a common type of electrochemical device, have become the most popular energy storage system due to their high operating voltage, long lifespan, and environmental friendliness, and are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids, and other fields.

[0003] With the widespread application of electrochemical devices in passenger vehicles, their safety performance has become a growing concern. Using gel electrolytes instead of traditional liquid electrolytes can effectively improve battery safety against overcharge, compression, and puncture. However, compared to liquid electrolytes, gel electrolytes often suffer from low ionic conductivity and high film impedance, which in turn affects the battery's internal resistance and cycle performance. Therefore, maintaining high safety performance while simultaneously ensuring good internal resistance and cycle performance remains a challenging technical problem for those skilled in the art. Summary of the Invention

[0004] In view of this, the main objective of the present invention is to provide an electrochemical device and a gel electrolyte. This electrochemical device can achieve a balance of low internal resistance, high cycling performance, and high safety performance.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] A first aspect of the present invention provides an electrochemical device comprising a gel electrolyte, a positive electrode, and a negative electrode, wherein the gel electrolyte comprises an acrylate polymer, a sulfur-containing additive, and a lithium salt additive, wherein the mass fraction of the acrylate polymer in the gel electrolyte is a, the mass fraction of the sulfur-containing additive is b, and the mass fraction of the lithium salt additive is c, and a, b, and c satisfy: 0.5 ≤ a / (b+c) < 10.

[0007] In some implementations, lithium salt additives include lithium difluorophosphate.

[0008] In some implementations, a, b, and c satisfy: 1.2 ≤ a / (b+c) ≤ 4.

[0009] In some implementations, b and c satisfy: 1% ≤ b + c ≤ 5%.

[0010] In some embodiments, the mass fraction a of the acrylate polymer in the gel electrolyte is 1% to 20%.

[0011] In some embodiments, the mass fraction b of the sulfur-containing additive in the gel electrolyte is 0.1% to 3%.

[0012] In some embodiments, the mass fraction c of the lithium salt additive in the gel electrolyte is 0.1% to 1%.

[0013] In some embodiments, the monomers of the acrylate polymer include one or more of isobutyl methacrylate, 2-bromoethyl acrylate, pentabromophenyl acrylate, and trimethylolpropane triacrylate.

[0014] In some embodiments, the sulfur-containing additive includes one or more of vinyl sulfate, methylene disulfonate, 1,3-propanesulfonate lactone, and 1,3-propenesulfonate lactone.

[0015] A second aspect of the present invention provides a gel electrolyte comprising an acrylate polymer, a sulfur-containing additive, and a lithium salt additive, wherein the mass fraction of the acrylate polymer is a, the mass fraction of the sulfur-containing additive is b, and the mass fraction of the lithium salt additive is c, and a, b, and c satisfy: 0.5 ≤ a / (b+c) < 10.

[0016] In some implementations, lithium salt additives include lithium difluorophosphate.

[0017] In some implementations, a, b, and c satisfy: 1.2 ≤ a / (b+c) ≤ 4.

[0018] In some implementations, b and c satisfy: 1% ≤ b + c ≤ 5%.

[0019] In some embodiments, the mass fraction a of the acrylate polymer in the gel electrolyte is 1% to 20%.

[0020] In some embodiments, the mass fraction b of the sulfur-containing additive in the gel electrolyte is 0.1% to 3%.

[0021] In some embodiments, the mass fraction c of the lithium salt additive in the gel electrolyte is 0.1% to 1%.

[0022] The electrochemical device disclosed in this application employs a gel electrolyte, which includes acrylate polymers, sulfur-containing additives, and lithium salt additives. The gel electrolyte provides good mechanical strength and elasticity, which is beneficial for achieving high safety performance in the electrochemical device. Furthermore, by adding sulfur-containing additives to the gel electrolyte, the sulfur element in the additives can undergo a reduction reaction during the operation of the electrochemical device, forming stable solid compounds such as lithium sulfide. These solid compounds can participate in the construction of the cathode electrolyte interface film (CEI) on the surface of the positive electrode and the solid electrolyte interphase (SEI) film on the surface of the negative electrode, thereby improving the stability of the battery device and thus enhancing its cycle performance. In addition, this application adds lithium salt additives to the gel electrolyte. Lithium salt additives help reduce the impedance of the CEI and SEI films, thereby reducing charge transfer impedance and promoting ion transport at the interface between the electrodes (positive and negative electrodes) and the gel electrolyte, thus reducing the internal resistance of the electrochemical device. Based on the above, by controlling 0.5≤a / (b+c)<10, the electrochemical device can achieve low internal resistance, high cycle performance, and high safety performance. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0024] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0025] Unless otherwise specified, the term "or" is inclusive in this invention. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0026] Unless otherwise specified, in this invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0027] The first aspect of this application provides an electrochemical device. This electrochemical device can be a cylindrical lithium-ion battery, a prismatic lithium-ion battery, a button-type lithium-ion battery, or a thin-film lithium-ion battery; however, the embodiments of this application are not limited to this type.

[0028] Typically, an electrochemical device includes a positive electrode, a negative electrode, and an electrolyte. During battery charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor of ions between the positive and negative electrodes and prevents short circuits between them.

[0029] The electrochemical device of this application includes a gel electrolyte, a positive electrode, and a negative electrode. The gel electrolyte includes an acrylate polymer, a sulfur-containing additive, and a lithium salt additive. In the gel electrolyte, the mass fraction of the acrylate polymer is a, the mass fraction of the sulfur-containing additive is b, and the mass fraction of the lithium salt additive is c. a, b, and c satisfy: 0.5 ≤ a / (b+c) < 10.

[0030] The electrochemical device disclosed in this application employs a gel electrolyte, which includes acrylate polymers, sulfur-containing additives, and lithium salt additives. The gel electrolyte provides good mechanical strength and elasticity, which is beneficial for achieving high safety performance in the electrochemical device. Furthermore, by adding sulfur-containing additives to the gel electrolyte, the sulfur element in the additives can undergo a reduction reaction during the operation of the electrochemical device, forming stable solid compounds such as lithium sulfide. These solid compounds can participate in the construction of the CEI film on the surface of the positive electrode and the SEI film on the surface of the negative electrode, thereby improving the stability of the battery device and thus enhancing its cycle performance. In addition, this application reduces the impedance of the CEI and SEI films by adding lithium salt additives to the gel electrolyte, thereby reducing charge transfer impedance and promoting ion transport at the interface between the electrodes (positive and negative electrodes) and the gel electrolyte, thus reducing the internal resistance of the electrochemical device.

[0031] Based on the above, in the gel electrolyte, the total mass percentage (b+c) of sulfur-containing additives and lithium salt additives reflects the uniformity, stability, and impedance of the CEI and SEI films. That is, the larger the mass percentage (b+c), the more uniform and stable the CEI and SEI films are, resulting in lower internal resistance and better cycle performance of the electrochemical device. In the gel electrolyte, the mass fraction (a) of acrylate polymers reflects the mechanical strength and elasticity of the gel electrolyte. That is, the larger the mass percentage (a) of the gel electrolyte, the better the mechanical strength and elasticity of the gel electrolyte, and the better the safety performance of the electrochemical device. Therefore, it is necessary to control the ratio of (a) to (b+c) in the gel electrolyte so that (a, b, c) satisfies the following relationship: 0.5 ≤ a / (b+c) < 10, thereby facilitating a balance between low internal resistance, high cycle performance, and high safety performance in the electrochemical device.

[0032] For example, a / (b+c) is any value within the range of 0.5, 1, 1.2, 2, 3, 4, 5, 6, 7, 8, 9, or any combination thereof.

[0033] In some implementations, a, b, and c satisfy: 1.2 ≤ a / (b+c) ≤ 4. A value of a / (b+c) within this range is more conducive to improving the mechanical strength and elasticity of the gel electrolyte while forming structurally stable CEI and SEI membranes with low internal resistance. This facilitates further reduction of internal resistance in the electrochemical device and further enhances its cycle performance and safety.

[0034] In some embodiments, b and c satisfy the condition: 1% ≤ b + c ≤ 5%. A value of b + c within this range reflects a moderate total amount of sulfur-containing additives and lithium salt additives, meaning that a structurally stable CEI and SEI membrane with low internal resistance can be formed without affecting the overall properties of the gel electrolyte. This is beneficial for reducing the internal resistance of the electrochemical device and improving its cycle performance. For example, b + c can be any value within the range of 1%, 2%, 3%, 4%, 5%, or any combination thereof.

[0035] The following is a further explanation of the components of the electrochemical device:

[0036] electrolytes

[0037] The electrolyte is positioned between the positive and negative electrodes, serving to conduct ions and prevent short circuits between the positive and negative electrodes. In this application, the electrolyte is a gel electrolyte, which includes acrylate polymers, sulfur-containing additives, and lithium salt additives.

[0038] In some embodiments, the lithium salt additive includes lithium difluorophosphate. By adding lithium difluorophosphate to the gel electrolyte, the impedance of the CEI and SEI films can be reduced, thereby reducing charge transfer impedance and promoting ion transport at the interface between the electrodes (positive and negative electrodes) and the gel electrolyte, thus reducing the internal resistance of the electrochemical device.

[0039] In some embodiments, the mass fraction 'a' of the acrylate polymer in the gel electrolyte is between 1% and 20%. A mass fraction 'a' of the acrylate polymer in the gel electrolyte within this range is advantageous because, during the synthesis of the gel electrolyte, the monomers of the acrylate polymer are cured in situ to form the gel electrolyte, thereby improving the safety performance of the electrochemical device. When 'a' is too low, incomplete monomer polymerization occurs, preventing the formation of a uniform gel polymer electrolyte, thus the improvement in the safety performance of the electrochemical device is not significant. When 'a' is too high, residual polymer monomers remain, thereby deteriorating the impedance and cycling performance of the electrochemical device. Exemplarily, the mass fraction 'a' of the acrylate polymer in the gel electrolyte is any value within the range of 1%, 2%, 4%, 6%, 8%, 10%, 15%, 20%, or any combination thereof.

[0040] In this application, the acrylate polymers have the structure shown in general formula I: CH2=C(R1)C(O)OC n H 2n+1 Formula I, wherein R1 includes, but is not limited to, one or more of alkyl, alkoxy, haloalkyl, ester, halophenyl, and halohydroxy groups. Halohydroxy groups include groups with the structural formula -OX, where X includes one of fluorine, chlorine, bromine, and iodine.

[0041] In some embodiments, the mass fraction b of the sulfur-containing additive in the gel electrolyte is 0.1% to 3%. A mass fraction b of the sulfur-containing additive in the gel electrolyte within this range is beneficial for the sulfur-containing additive to help form a stable CEI film on the surface of the positive electrode and a stable SEI film on the surface of the negative electrode, thereby improving the cycle performance of the electrochemical device. Exemplarily, the mass fraction b of the sulfur-containing additive in the gel electrolyte is any value within the range of 0.1%, 0.5%, 1%, 2%, 3%, or any combination thereof.

[0042] In some embodiments, the mass fraction c of the lithium salt additive in the gel electrolyte is from 0.1% to 1%. A mass fraction c of lithium salt additive in the gel electrolyte within this range is beneficial for the lithium salt additive to form a low-resistance interfacial film on the surfaces of the positive and negative electrode plates, thereby reducing charge transfer impedance and promoting ion transport at the electrode-electrolyte interface, thus reducing the internal resistance of the electrochemical device. Exemplarily, the mass fraction c of lithium salt additive in the gel electrolyte is any value within the range of 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, or any combination thereof.

[0043] In some embodiments, the monomers of the acrylate polymer include at least one selected from isobutyl methacrylate, 2-bromoethyl acrylate, pentabromophenyl acrylate, and trimethylolpropane triacrylate. The raw materials for these monomers are readily available, which can reduce the production cost of the electrochemical device.

[0044] In some embodiments, the monomers of the acrylate polymers further include one or more of the following: methyl methacrylate, acrylonitrile, methoxy polyethylene glycol methacrylate, hydroxypropyl acrylate, isostearyl acrylate, 4-hydroxybutyl acrylate, tributyltin acrylate, propane-1,3-dimethyl diacrylate, 4-ethylphenyl acrylate, hydroxyethyl acrylate, hydroxypentabromophenyl methacrylate, 6-bromo-1-hexyl acrylate, 2-bromoethyl acrylate, 2-chloroethyl methacrylate, undecyl 11-phosphonate, tributyltin acrylate, and 2-(perfluorobutyl)ethyl acrylate.

[0045] In some embodiments, the sulfur-containing additives include one or more of vinyl sulfate (DTD), methylene methane disulfonate (MMDS), 1,3-propanesulfonate lactone (PS), and 1,3-propenesulfonate lactone (PST). These sulfur-containing additives can help form a stable CEI film on the surface of the positive electrode and a stable SEI film on the surface of the negative electrode, thereby improving the cycle performance of the electrochemical device.

[0046] In some embodiments, the lithium salt additives also include one or more of lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium difluorooxalate phosphate. Adding these lithium salt additives helps to further reduce the internal resistance of the electrochemical device.

[0047] In some embodiments, the gel electrolyte further includes an initiator, the initiator comprising, by mass fraction, 0.1% to 5% of the acrylate polymer in the gel electrolyte. A mass fraction of the initiator within this range facilitates in-situ curing of the acrylate polymer monomers to form the gel electrolyte, thereby improving the safety performance of the electrochemical device. Exemplarily, the mass fraction of the initiator in the gel electrolyte is any value within the range of 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5% of the acrylate polymer in the gel electrolyte, or any combination thereof.

[0048] In some embodiments, the initiator includes any initiator known in the art that can be used to initiate free radical polymerization and copolymerization reactions of olefins and dienes.

[0049] In some embodiments, the initiator includes one or more of azobisisobutyronitrile, azobisisoheptanenitrile, potassium persulfate, ammonium persulfate, lauroyl peroxide, benzoyl peroxide, and dodecyl peroxide.

[0050] In some embodiments, the gel electrolyte further includes a solvent, which includes one or more of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethyl acetate (EA), and propyl acetate (PA).

[0051] In some embodiments, the gel electrolyte further includes an electrolyte salt, the mass fraction of which is 0.1% to 2%. A mass fraction of the electrolyte salt within this range facilitates the dissociation of ions from the electrolyte salt within the gel electrolyte, thereby promoting ion transport between the positive and negative electrodes and maintaining charge balance, thus improving the cycle performance and safety of the electrochemical device. Exemplarily, the mass fraction of the electrolyte salt in the gel electrolyte is any value within the range of 0.1%, 0.5%, 1%, 1.5%, 2%, or any combination thereof.

[0052] In some embodiments, the electrolyte salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0053] In some embodiments, the gel electrolyte further includes an additive containing unsaturated bonds, wherein the mass fraction of the additive containing unsaturated bonds in the gel electrolyte is 0.1% to 2%. A mass fraction of the additive containing unsaturated bonds in the gel electrolyte within the above range is beneficial for the additive containing unsaturated bonds to form a uniform, stable solid electrolyte interface (CEI) film with good ion transport properties on the surface of the positive electrode, thereby helping to reduce the internal resistance of the electrochemical device and improving its cycle performance and safety. Exemplarily, the mass fraction of the additive containing unsaturated bonds in the gel electrolyte is any value within the range of 0.1%, 0.5%, 1%, 1.5%, 2%, or any combination thereof.

[0054] In this application, additives containing unsaturated bonds refer to additives containing double or triple bonds. Their molecular structure contains substituent groups (i.e., unsaturated bonds) with double or triple bonds. These unsaturated bonds endow these compounds with high chemical reactivity, allowing them to readily undergo bond-breaking polymerization reactions, thereby forming a uniform, stable, and highly ion-transporting solid electrolyte interphase (CEI) film on the surface of the positive electrode layer. The double bonds include, but are not limited to, carbon-carbon double bonds and carbon-oxygen double bonds, while the triple bonds include, but are not limited to, carbon-carbon triple bonds and carbon-nitrogen triple bonds.

[0055] In some embodiments, the additives containing unsaturated bonds include one or more of vinylene carbonate (VC) and tripropynyl phosphate (TP).

[0056] In some embodiments, the gel electrolyte further includes an acid-removing additive, the mass fraction of which is 0.1% to 2%. A mass fraction of the acid-removing additive in the gel electrolyte within this range is beneficial for improving the interfacial properties, electrochemical performance, and long-term stability of the electrochemical device, thereby enhancing the overall performance of the electrochemical device. Exemplarily, the mass fraction of the acid-removing additive in the gel electrolyte is any value within the range of 0.1%, 0.5%, 1%, 1.5%, 2%, or any combination thereof.

[0057] In some embodiments, the acid-removing additive includes one or more of tris(trimethylsilane)phosphate (TMSP) and tris(trimethylsilane)borate (TMSB).

[0058] Positive electrode sheet

[0059] In this application, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0060] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0061] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0062] In some embodiments, when the electrochemical device is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0063] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0064] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0065] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0066] Negative electrode sheet

[0067] In this application, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0068] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0069] In some implementations, the negative electrode current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil.

[0070] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0071] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0072] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0073] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0074] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0075] Separating membrane

[0076] In some embodiments, the electrochemical device also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0077] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0078] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0079] A second aspect of this application provides a gel electrolyte. The gel electrolyte comprises an acrylate polymer, a sulfur-containing additive, and a lithium salt additive. In the gel electrolyte, the mass fraction of the acrylate polymer is a, the mass fraction of the sulfur-containing additive is b, and the mass fraction of the lithium salt additive is c. a, b, and c satisfy: 0.5 ≤ a / (b+c) < 10.

[0080] In some implementations, lithium salt additives include lithium difluorophosphate.

[0081] In some implementations, a, b, and c satisfy: 1.2 ≤ a / (b+c) ≤ 4.

[0082] In some implementations, b and c satisfy: 1% ≤ b + c ≤ 5%.

[0083] In some embodiments, the mass fraction a of the acrylate polymer in the gel electrolyte is 1% to 20%.

[0084] In some embodiments, the mass fraction b of the sulfur-containing additive in the gel electrolyte is 0.1% to 3%.

[0085] In some embodiments, the mass fraction c of the lithium salt additive in the gel electrolyte is 0.1% to 1%.

[0086] Example 1

[0087] The preparation method of the electrochemical device is as follows:

[0088] (1) Preparation of positive electrode sheet

[0089] Lithium nickel cobalt manganese oxide (LiNi) is used as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black (Super P), polyvinylidene fluoride (PVDF) and carbon nanotubes (CNT) are mixed in the solvent N-methylpyrrolidone at a weight ratio of 97.6:0.8:1:0.6 and stirred evenly to obtain the positive electrode slurry.

[0090] Aluminum foil was used as the positive electrode current collector, and the positive electrode slurry was coated on both sides of the positive electrode current collector with a coating amount of 260 g / m². 2 The positive electrode sheet is prepared by baking at 85°C for 1 hour, followed by cold pressing, cutting, and slitting.

[0091] (2) Preparation of negative electrode sheet

[0092] The negative electrode active materials, artificial graphite, conductive carbon black (Super P), carbon nanotubes (CNT), sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), were mixed in deionized water at a weight ratio of 95.64:1:0.06:1.3:2 and stirred evenly to obtain the negative electrode slurry.

[0093] Copper foil was used as the negative electrode current collector, and the negative electrode slurry was coated on both sides of the negative electrode current collector with a coating amount of 156 g / m². 2 The negative electrode sheet is prepared by baking at 120°C for 1 hour, followed by cold pressing, cutting, and slitting.

[0094] (3) Preparation of electrolytes

[0095] In an argon atmosphere, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a mass ratio of 3:7 to obtain a mixed solvent. To this mixed solvent, the electrolyte salt lithium hexafluorophosphate (LiPF6), sulfur-containing additives vinyl sulfate (DTD) and 1,3-propanesulfonate lactone (PS), lithium salt additive lithium difluorophosphate (LiPO2F2), polymer monomer isobutyl methacrylate, and initiator azobisisobutyronitrile are added to obtain an electrolyte. The electrolyte contains 5% isobutyl methacrylate monomer (a), 1.5% vinyl sulfate, 0.5% 1,3-propanesulfonate lactone (i.e., 2% sulfur-containing additive (b)), 0.5% lithium difluorophosphate (c), 13% lithium hexafluorophosphate, and 0.05% azobisisobutyronitrile.

[0096] (4) Preparation of the separating membrane

[0097] A polyethylene film with a thickness of 12 μm was used as the separator.

[0098] (5) Assembly of electrochemical devices

[0099] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode to provide isolation. The stacked positive electrode, separator, and negative electrode are then placed into an aluminum-plastic film to obtain the electrode assembly.

[0100] After baking the electrode assembly under vacuum at 95°C for 24 hours, the electrolyte was injected into the electrode assembly and immersed at room temperature for 72 hours to ensure uniform electrolyte wetting. Then, the electrode assembly was cured at 60°C for 6 hours to form a gel electrolyte. The electrode assembly was then formed at 45°C and aged at room temperature for 24 hours to obtain the electrochemical device.

[0101] The performance of the obtained electrochemical device was tested using the following methods:

[0102] Direct Current Resistance (DCR) Test:

[0103] At 25°C, the electrochemical device prepared in Example 1 was charged to 4.25V with a constant current of 0.33C, and then discharged with a constant current of 0.33C for 30 minutes. The voltage V1 was recorded. After standing for 10 minutes, it was discharged with a constant current of 4C for 10 seconds. The voltage V2 was recorded. The DC resistance DCR of the electrochemical device was calculated as (V2-V1) / current. The test results are recorded in Table 1 below.

[0104] Cyclic performance test:

[0105] At 25°C, the electrochemical device prepared in Example 1 was charged to 4.25V with a constant current of 1C to reach a fully charged state, and then discharged to 2.5V with a constant current of 1C to reach a fully discharged state, which is the first cycle. The discharge capacity of the first cycle is denoted as C0.

[0106] The above steps are repeated n times. The discharge capacity of the nth cycle is denoted as Cn, and the capacity retention rate of the nth cycle is (Cn / C0)*100%. The above charge-discharge cycle is repeated, and the number of cycles when the capacity retention rate is 80% is recorded. The test results are recorded in Table 1 below.

[0107] Security performance test:

[0108] The electrochemical device prepared in Example 1 was charged to 4.25V with a constant current of 0.33C. A high-temperature resistant steel needle with a diameter of 6mm was inserted into the electrochemical device at a speed of 25±5mm / s. During and after the needle insertion, the changes (ignition) on the surface of the electrochemical device were observed and recorded. The test results are recorded in Table 1 below.

[0109] Example 2

[0110] The electrochemical device was prepared using the same method as in Example 1, except that at least one of the following was adjusted according to Table 1: the mass fraction a of the acrylate polymer in the gel electrolyte, the mass fraction b of the sulfur-containing additive in the gel electrolyte, and the mass fraction c of the lithium salt additive in the gel electrolyte. In Example 2, a / (b+c) was 0.5.

[0111] Example 3

[0112] The electrochemical device was prepared using the same method as in Example 1, except that at least one of the following was adjusted according to Table 1: the mass fraction a of the acrylate polymer in the gel electrolyte, the mass fraction b of the sulfur-containing additive in the gel electrolyte, and the mass fraction c of the lithium salt additive in the gel electrolyte. In Example 3, a / (b+c) was 1.2.

[0113] Example 4

[0114] The electrochemical device was prepared using the same method as in Example 1, except that at least one of the following was adjusted according to Table 1: the mass fraction a of the acrylate polymer in the gel electrolyte, the mass fraction b of the sulfur-containing additive in the gel electrolyte, and the mass fraction c of the lithium salt additive in the gel electrolyte. In Example 4, a / (b+c) was 4.

[0115] Example 5

[0116] The electrochemical device was prepared using the same method as in Example 1, except that at least one of the following was adjusted according to Table 1: the mass fraction a of the acrylate polymer in the gel electrolyte, the mass fraction b of the sulfur-containing additive in the gel electrolyte, and the mass fraction c of the lithium salt additive in the gel electrolyte. In Example 5, a / (b+c) was 8.

[0117] Comparative Example 1

[0118] The electrochemical device was prepared using the same method as in Example 1, except that in Comparative Example 1, isobutyl methacrylate and azobisisobutyronitrile were not added to the electrolyte.

[0119] Comparative Example 2

[0120] The electrochemical device was prepared using the same method as in Example 1, except that in Comparative Example 2, isobutyl methacrylate and azobisisobutyronitrile were not added to the electrolyte, and the mass fraction of DTD was adjusted to 1% according to Table 1 below.

[0121] Comparative Example 3

[0122] The electrochemical device was prepared using the same method as in Example 1, except that in Comparative Example 3, no sulfur-containing additive (ethylene sulfate) was added to the gel electrolyte.

[0123] Comparative Example 4

[0124] The electrochemical device was prepared using the same method as in Example 1, except that no lithium salt additive (lithium difluorophosphate) was added to the gel electrolyte in Comparative Example 4.

[0125] Comparative Example 5

[0126] The electrochemical device was prepared in the same manner as in Example 1, except that at least one of the following was adjusted according to Table 1: the mass fraction a of the acrylate polymer in the gel electrolyte, the mass fraction b of the sulfur-containing additive in the gel electrolyte, and the mass fraction c of the lithium salt additive in the gel electrolyte. In Comparative Example 5, a / (b+c) was 11.54.

[0127] Comparative Example 6

[0128] The electrochemical device was prepared in the same manner as in Example 1, except that at least one of the following was adjusted according to Table 1: the mass fraction a of the acrylate polymer in the gel electrolyte, the mass fraction b of the sulfur-containing additive in the gel electrolyte, and the mass fraction c of the lithium salt additive in the gel electrolyte. In Comparative Example 6, a / (b+c) was 10.

[0129] Comparative Example 7

[0130] The electrochemical device was prepared in the same manner as in Example 1, except that at least one of the following was adjusted according to Table 1: the mass fraction a of the acrylate polymer in the gel electrolyte, the mass fraction b of the sulfur-containing additive in the gel electrolyte, and the mass fraction c of the lithium salt additive in the gel electrolyte. In Comparative Example 7, a / (b+c) was 0.43.

[0131] Comparative Example 8

[0132] The electrochemical device was prepared in the same manner as in Example 1, except that at least one of the following was adjusted according to Table 1: the mass fraction a of the acrylate polymer in the gel electrolyte, the mass fraction b of the sulfur-containing additive in the gel electrolyte, and the mass fraction c of the lithium salt additive in the gel electrolyte. In Comparative Example 8, a / (b+c) was 0.48.

[0133] The electrochemical devices obtained in Examples 1 to 5 and Comparative Examples 1 to 8 were tested using the same test methods as in Example 1. The test results of Examples 1 to 5 and Comparative Examples 1 to 8 are shown in Table 1 below.

[0134] Table 1

[0135]

[0136] As can be seen from the data in Table 1, compared to Comparative Examples 1 and 2 (the electrolyte does not contain acrylate polymers, i.e., the electrolyte is still liquid in the electrochemical device after formation), Comparative Example 3 (the gel electrolyte does not contain sulfur-containing additives), Comparative Example 4 (the gel electrolyte does not contain lithium salt additives), Comparative Examples 5 and 6 (a / (b+c) is greater than or equal to 10), and Comparative Examples 7 and 8 (a / (b+c) is less than 0.5), Examples 1 to 5, by adding acrylate polymers, sulfur-containing additives, and lithium salt additives to the gel electrolyte and controlling the mass fraction of the three in the gel electrolyte to satisfy 0.5 ≤ a / (b+c) < 10, enable the electrochemical device to achieve low internal resistance, high cycle performance, and high safety performance. In particular, when 1.2 ≤ a / (b+c) ≤ 4, the internal resistance of the electrochemical device is further reduced, and the cycle performance and safety performance are further improved.

[0137] Example 6

[0138] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction b of the sulfur-containing additive in the gel electrolyte and the mass fraction c of the lithium salt additive in the gel electrolyte were different. In Example 6, b+c was 1%.

[0139] Example 7

[0140] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction b of the sulfur-containing additive in the gel electrolyte and the mass fraction c of the lithium salt additive in the gel electrolyte were different. In Example 7, b+c was 5%.

[0141] The electrochemical devices obtained in Examples 6 and 7 were tested using the same testing methods as in Example 1. The test results for Examples 6 and 7 are shown in Table 2 below. For ease of comparison, the data from Example 1 are also shown.

[0142] Table 2

[0143]

[0144]

[0145] As can be seen from the data in Table 2, when the relationship between the mass fraction b of sulfur-containing additives in the gel electrolyte and the mass fraction c of lithium salt additives in the gel electrolyte satisfies 1% ≤ b + c ≤ 5%, the resulting electrochemical device can achieve a balance between low internal resistance, high cycle performance, and high safety performance.

[0146] Example 8

[0147] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction a of the acrylate polymer in the gel electrolyte was different; in Example 8, a was 8%.

[0148] Example 9

[0149] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction a of the acrylate polymer in the gel electrolyte was different; in Comparative Example 7, a was 15%.

[0150] The electrochemical devices obtained in Examples 8 and 9 were tested using the same testing methods as in Example 1. The test results for Examples 8 and 9 are shown in Table 3 below. For ease of comparison, the data from Examples 1 to 5 are also shown.

[0151] Table 3

[0152]

[0153] The data in Table 3 show that when the mass fraction 'a' of acrylate polymers in the gel electrolyte is in the range of 1% to 20%, the resulting electrochemical device can achieve a balance of low internal resistance, high cycling performance, and high safety. In particular, a mass fraction 'a' in the range of 1% to 10% is beneficial for further reducing the internal resistance of the electrochemical device.

[0154] Example 10

[0155] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction b of the sulfur-containing additive in the gel electrolyte was different; in Example 10, b was 0.1%.

[0156] Example 11

[0157] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction b of the sulfur-containing additive in the gel electrolyte was different; in Example 11, b was 1.5%.

[0158] Example 12

[0159] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction b of the sulfur-containing additive in the gel electrolyte was different; in Example 12, b was 2.5%.

[0160] Example 13

[0161] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction b of the sulfur-containing additive in the gel electrolyte was different; in Example 13, b was 0.5%.

[0162] Example 14

[0163] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction b of the sulfur-containing additive in the gel electrolyte was different; in Example 14, b was 3%.

[0164] The electrochemical devices obtained in Examples 10 to 14 were subjected to performance tests using the same test methods as in Example 1. The test results for Examples 10 to 14 are shown in Table 4 below. For ease of comparison, the data from Example 1 are also shown.

[0165] Table 4

[0166]

[0167] As can be seen from the data in Table 4, when the mass fraction b of the sulfur-containing additive in the gel electrolyte is in the range of 0.1% to 3%, the resulting electrochemical device can achieve a balance between low internal resistance, high cycle performance, and high safety performance. In particular, when b is in the range of 1% to 3%, the cycle performance of the battery device can be further improved.

[0168] Example 15

[0169] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction c of the lithium salt additive in the gel electrolyte was different; in Example 15, c was 0.1%.

[0170] Example 16

[0171] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction c of the lithium salt additive in the gel electrolyte was different; in Example 16, c was 0.3%.

[0172] Example 17

[0173] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction c of the lithium salt additive in the gel electrolyte was different; in Example 17, c was 0.8%.

[0174] Example 18

[0175] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction c of the lithium salt additive in the gel electrolyte was different; in Example 18, c was 1%.

[0176] The electrochemical devices obtained in Examples 15 to 18 were subjected to performance tests using the same test methods as in Example 1. The test results for Examples 15 to 18 are shown in Table 5 below. For ease of comparison, the data from Example 1 are also shown.

[0177] Table 5

[0178]

[0179]

[0180] As can be seen from the data in Table 5, when the mass fraction c of lithium salt additives in the gel electrolyte is in the range of 0.1% to 1%, the resulting electrochemical device can achieve a balance of low internal resistance, high cycle performance, and high safety performance.

[0181] Example 19

[0182] The electrochemical device was prepared using the same method as in Example 1, except that in Example 19, 2-bromoethyl acrylate was used as the monomer of the acrylate polymer.

[0183] Example 20

[0184] The electrochemical device was prepared using the same method as in Example 1, except that in Example 20, pentabromophenyl acrylate was used as the monomer of the acrylate polymer.

[0185] Example 21

[0186] The electrochemical device was prepared using the same method as in Example 1, except that in Example 21, trimethylolpropane triacrylate was used as the monomer of the acrylate polymer.

[0187] The electrochemical devices obtained in Examples 19 to 21 were subjected to performance tests using the same testing methods as in Example 1. The test results for Examples 19 to 21 are shown in Table 6 below. For ease of comparison, the data from Example 1 are also shown.

[0188] Table 6

[0189]

[0190] As can be seen from the data in Table 6, Examples 1 and 19 to 21, by adding monomers of the above-mentioned types of acrylate polymers to the electrolyte, enable the electrochemical device to achieve low internal resistance, high cycling performance, and high safety performance.

[0191] Example 22

[0192] The electrochemical device was prepared using the same method as in Example 1, except that in Example 22, ethylene sulfate (DTD) and methylene disulfonate (MMDS) were used as sulfur-containing additives, and the mass fraction c of lithium salt additives in the gel electrolyte was 0.3%.

[0193] Example 23

[0194] The electrochemical device was prepared using the same method as in Example 1, except that in Example 23, vinyl sulfate (DTD) and 1,3-propenesulfonyl lactone (PST) were used as sulfur-containing additives, and the mass fraction c of the lithium salt additive in the gel electrolyte was 0.8%.

[0195] The electrochemical devices obtained in Examples 22 and 23 were tested using the same testing methods as in Example 1. The test results for Examples 22 and 23 are shown in Table 7 below. For ease of comparison, the data from Example 1 are also shown.

[0196] Table 7

[0197]

[0198] As can be seen from the data in Table 7, Examples 1, 22, and 23, by adding the above-mentioned sulfur-containing additives to the gel electrolyte, enable the electrochemical device to achieve low internal resistance, high cycling performance, and high safety performance.

[0199] Example 24

[0200] The electrochemical device was prepared using the same method as in Example 1, except that in Example 24, lithium tetrafluorophosphate was selected as the lithium salt additive.

[0201] The electrochemical device obtained in Example 24 was tested using the same testing methods as in Example 1. The test results for Example 24 are shown in Table 8 below. For ease of comparison, the data from Example 1 are also shown.

[0202] Table 8

[0203]

[0204] As can be seen from the data in Table 7, Examples 1 and 24, by adding the aforementioned types of lithium salt additives to the gel electrolyte, enabled the electrochemical devices to achieve a balance of low internal resistance, high cycle performance, and high safety performance. In particular, when the lithium salt additive is lithium difluorophosphate, the internal resistance of the electrochemical device can be further reduced.

[0205] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An electrochemical device, characterized in that, The electrochemical device includes a gel electrolyte, a positive electrode, and a negative electrode, wherein the gel electrolyte includes an acrylate polymer, a sulfur-containing additive, and a lithium salt additive. In the gel electrolyte, the mass fraction of the acrylate polymer is a, the mass fraction of the sulfur-containing additive is b, and the mass fraction of the lithium salt additive is c. The mass fraction of a, b, and c satisfies: 0.5 ≤ a / (b+c) < 10.

2. The electrochemical device according to claim 1, characterized in that, The lithium salt additives include lithium difluorophosphate.

3. The electrochemical device according to claim 1 or 2, characterized in that, The condition a, b, and c satisfy: 1.2 ≤ a / (b+c) ≤ 4.

4. The electrochemical device according to claim 1 or 2, characterized in that, The condition b and c satisfy the following: 1% ≤ b + c ≤ 5%.

5. The electrochemical device according to any one of claims 1 to 4, characterized in that, The mass fraction (a) of the acrylate polymer in the gel electrolyte is 1% to 20%.

6. The electrochemical device according to any one of claims 1 to 5, characterized in that, The sulfur-containing additive has a mass fraction b of 0.1% to 3% in the gel electrolyte.

7. The electrochemical device according to any one of claims 1 to 6, characterized in that, The lithium salt additive has a mass fraction (c) of 0.1% to 1% in the gel electrolyte.

8. The electrochemical device according to any one of claims 1 to 7, characterized in that, The monomers of the acrylate polymers include one or more of isobutyl methacrylate, 2-bromoethyl acrylate, pentabromophenyl acrylate, and trimethylolpropane triacrylate.

9. The electrochemical device according to any one of claims 1 to 8, characterized in that, The sulfur-containing additives include one or more of vinyl sulfate, methylene disulfonate, 1,3-propanesulfonate lactone, and 1,3-propenesulfonate lactone.

10. A gel electrolyte, characterized in that, The gel electrolyte comprises acrylate polymers, sulfur-containing additives, and lithium salt additives. In the gel electrolyte, the mass fraction of the acrylate polymer is a, the mass fraction of the sulfur-containing additive is b, and the mass fraction of the lithium salt additive is c. The mass fraction of a, b, and c satisfies: 0.5 ≤ a / (b+c) < 10.

11. The gel electrolyte according to claim 10, characterized in that, The lithium salt additives include lithium difluorophosphate.

12. The gel electrolyte according to claim 10 or 11, characterized in that, The condition a, b, and c satisfy: 1.2 ≤ a / (b+c) ≤ 4.

13. The gel electrolyte according to claim 10 or 11, characterized in that, The condition b and c satisfy the following: 1% ≤ b + c ≤ 5%.

14. The gel electrolyte according to any one of claims 10 to 13, characterized in that, The mass fraction (a) of the acrylate polymer in the gel electrolyte is 1% to 20%.

15. The gel electrolyte according to any one of claims 10 to 14, characterized in that, The sulfur-containing additive has a mass fraction b of 0.1% to 3% in the gel electrolyte.

16. The gel electrolyte according to any one of claims 10 to 15, characterized in that, The lithium salt additive has a mass fraction (c) of 0.1% to 1% in the gel electrolyte.

Images