Electrochemical device and electronic apparatus

Abstract

An electrochemical device includes a positive electrode tab and a negative electrode tab, the positive electrode tab includes a positive electrode current collector and a positive electrode active material layer, the negative electrode tab includes a negative electrode current collector and a negative electrode active material layer, the positive electrode active material layer includes at least one of a first additive and a second additive, the first additive is a solid-state electrolyte, and a chemical coefficient of Li in a molecular formula of the solid-state electrolyte is greater than 0.5, the second additive is a polymer containing a polyacrylonitrile functional group, the negative electrode active material layer includes at least one of a third additive and a fourth additive, the third additive is a solid-state electrolyte, and a chemical coefficient of Li in a molecular formula of the solid-state electrolyte is less than 1, and the fourth additive is a polymer containing a polyacrylonitrile functional group or a sulfurized polyacrylonitrile. The application also provides an electronic device including the electrochemical device. The application can significantly improve the pass rate of overcharge / thermal box test of the electrochemical device by adding a small amount of additives in the positive electrode and the negative electrode, respectively.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, and in particular to an electrochemical device and an electronic device comprising the same. BACKGROUND

[0002] With the rapid development of lithium ion batteries, people's demand for the energy density of lithium ion batteries is increasing. At present, the main effective means to improve the energy density of lithium ion batteries is to increase the charging voltage of lithium cobalt oxide cathode to make the cathode release more lithium ions to increase the capacity. When the charging voltage of the battery using lithium cobalt oxide cathode is increased to above 4.45V, the cathode will release too much lithium, and the activity will be very strong, which is more likely to react with the electrolyte at high temperature, resulting in the destruction of the layered structure of the cathode, the release of lattice oxygen, the dissolution of cobalt metal, etc. At the same time, the negative electrode also embeds more lithium, and the lithium embedded in the negative electrode at high temperature is also easy to react with the electrolyte, producing some reducing gases and destroying the structure of the positive electrode. At present, the main ways to improve the safety of high-voltage lithium cobalt oxide batteries are flame-retardant electrolyte, lithium cobalt oxide material coating / doping modification, graphite material coating / surface treatment modification, etc. Some of these methods use fluorine-containing chemicals that are prohibited by regulations, and some methods will lose a lot of energy density (voltage > 4.45V). SUMMARY

[0003] In view of this, the first aspect of the present application provides an electrochemical device, comprising a positive electrode sheet and a negative electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, the positive electrode active material layer comprising at least one of a first additive and a second additive, the first additive being a solid-state electrolyte, and the chemical coefficient of Li in the molecular formula of the solid-state electrolyte being greater than 0.5, the second additive being a polymer containing a polyacrylonitrile functional group, the mass percentage of the first additive being 0.1% to 3% based on the mass of the positive electrode active material layer, and the mass percentage of the second additive being 0.05% to 3% based on the mass of the positive electrode active material layer; the negative electrode active material layer comprises at least one of a third additive and a fourth additive, the third additive being a solid-state electrolyte, and the chemical coefficient of Li in the molecular formula of the solid-state electrolyte being less than 1, the fourth additive being a polymer containing a polyacrylonitrile functional group or a sulfurized polyacrylonitrile, the mass percentage of the third additive being 0.1% to 3% based on the mass of the negative electrode active material layer, and the mass percentage of the fourth additive being 0.05% to 3% based on the mass of the negative electrode active material layer.

[0004] When the coefficient of Li in the molecular formula structure of the solid-state electrolyte in the positive electrode exceeds 0.5, for the high-voltage lithium cobalt oxide system, the degree of lithium extraction of the positive electrode LiCoO2 exceeds Li xCoO2(x<0.5), thus, Li + The role of migrating and supplementing lithium source to the positive active material. The polyacrylonitrile functional group-containing polymer can occur affinity with the cobalt of the positive electrode through the N element of the cyano group in the molecule, so as to reduce the reaction degree of the positive electrode and the electrolyte, so that the heat generation inside the electrochemical device under abuse conditions is alleviated, and when the positive electrode is over-lithiated, the polyacrylonitrile functional group-containing polymer can also capture Li + The role of migrating and supplementing lithium source to the positive active material. The polyacrylonitrile functional group-containing polymer can occur affinity with the cobalt of the positive electrode through the N element of the cyano group in the molecule, so as to reduce the reaction degree of the positive electrode and the electrolyte, so that the heat generation inside the electrochemical device under abuse conditions is alleviated, and when the positive electrode is over-lithiated, the polyacrylonitrile functional group-containing polymer can also capture Li

[0005] In some embodiments, the mass average molecular weight of the second additive and the fourth additive is in the range of 3000 to 500000. Further improve the safety performance of the electrochemical device.

[0006] In some embodiments, the ratio of the molar content of nitrogen element and carbon element in the polyacrylonitrile functional group-containing polymer in the second additive and the fourth additive satisfies the following relationship: 0.03≤N / C<0.33. When the N / C molar ratio is closer to 0.33, the content of polyacrylonitrile (PAN) in the polymer is closer to 100%, and when the N / C molar ratio decreases, the proportion of polyacrylonitrile in the polymer decreases. Controlling the molar content ratio of N / C in the polyacrylonitrile functional group-containing polymer to be 0.03≤N / C<0.33, the electrochemical device has higher energy density and improved safety performance.

[0007] In some embodiments, the polyacrylonitrile functional group-containing polymer comprises at least one of the following repeating units: Wherein n≥2. The polyacrylonitrile functional group-containing polymer containing PAA repeating units is beneficial to improve the bonding performance, the polyacrylonitrile functional group-containing polymer containing PEO repeating units is beneficial to improve the ion conductivity of the polymer molecules, and the polyacrylonitrile functional group-containing polymer containing PMMA repeating units is beneficial to improve the flexibility of the polymer.

[0008] In some embodiments, the ratio of the molar content of nitrogen element and carbon element N / C and the ratio of the molar content of sulfur element and carbon element S / C in the sulfurized polyacrylonitrile satisfy the following relationship: 0.29 < N / C < 0.33, 0.53 < S / C < 1.6. The higher the S / C ratio in the sulfurized polyacrylonitrile, the higher the relative content of sulfur in the sulfurized polyacrylonitrile, and the better the affinity for lithium ions at high temperature. Controlling the molar content ratio of N / C in the sulfurized polyacrylonitrile to be 0.29 < N / C < 0.33 and the molar content ratio of S / C to be 0.53 < S / C < 1.6, the electrochemical device has a high energy density and improved safety performance.

[0009] In some embodiments, the sulfurized polyacrylonitrile comprises the following repeating unit:

[0010] wherein n > 2. The presence of PAA repeating units in the sulfurized polyacrylonitrile is beneficial to improve the bonding performance.

[0011] In some embodiments, the mass content of sulfur element in the sulfurized polyacrylonitrile is 20wt% to 60wt%. The safety performance of the electrochemical device can be further improved.

[0012] In some embodiments, the particle size distribution of the solid-state electrolyte in the first additive and the third additive satisfies the following relationship: Dv90 is 0.1 μm to 10 μm, and Dv50 is 0.1 μm to 1 μm. By controlling the approximate particle size range of the solid-state electrolyte to satisfy the above range, the thermal chamber test / overcharge performance of the battery can be improved.

[0013] In some embodiments, the powder ionic conductivity of the solid-state electrolyte in the first additive and the third additive is greater than or equal to 10 -7 S / cm. The powder ionic conductivity of the solid-state electrolyte is large, which is beneficial to the insertion and extraction of lithium ions at low temperature, thereby improving the low-temperature discharge performance of the battery.

[0014] In some embodiments, the voltage of the electrochemical device when fully charged is greater than or equal to 4.45V. By adding a small amount of a specific positive electrode additive to the positive electrode and a small amount of a specific negative electrode additive to the negative electrode, the charging voltage of the above-mentioned electrochemical device can be effectively increased to more than 4.45V.

[0015] The second aspect of the present application provides an electronic device comprising the above-mentioned electrochemical device. The above-mentioned electrochemical device is used as the power source of the electronic device, and the electrochemical device has stable performance and can stably supply power to the electronic device. DETAILED DESCRIPTION

[0016] The embodiments of the present application will be described below with reference to the embodiments of the present application. The data range values recorded in the present application should include the end values unless otherwise specified.

[0017] The present application provides an electrochemical device, which includes a negative electrode, a positive electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode. The positive electrode tab includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The negative electrode tab includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. In some embodiments, the full charge voltage of the electrochemical device is greater than or equal to 4.45 V.

[0018] The electrochemical device of the present application can be a lithium ion battery, but is not limited thereto, and can be any other suitable electrochemical device.

[0019] It should be noted that the following content of the present application uses a lithium ion battery as an example to explain the present application, but the electrochemical device of the present application is not limited to a lithium ion battery.

[0020] In the present application, the positive electrode active material layer and the negative electrode active material layer are respectively added with a specific additive. The positive electrode active material layer includes at least one of a first additive and a second additive. The first additive is a solid-state electrolyte, and the chemical coefficient of Li in the molecular formula of the solid-state electrolyte is greater than 0.5, for example, Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li 1.5 Al 0.3 Ti 1.5 (PO4)3, Li 1.4 Al 0.4 Ti 1.6 (PO4)3, Li7La3Zr2O 12 , Nb 0.25 Li 6.75 La3Zr2O 12 , Li7La3Zr 1.75 Nb 0.25 O 12 , Li 6.75 La3Zr 1.75 Ta 0.25 O 12 , Li 6.4 La3Zr 1.4 Ta 0.6 O 12 When the coefficient of Li in the molecular formula structure of the solid-state electrolyte in the positive electrode exceeds 0.5, for the high-voltage lithium cobaltate system, the degree of delithiation of the positive electrode LiCoO2 exceeds Li x CoO2(x<0.5), therefore, Li+ The second additive is a polymer containing polyacrylonitrile functional groups, and can be a polymer of acrylonitrile and other monomers. The polymer containing polyacrylonitrile functional groups can reduce the reaction between the positive electrode and the electrolyte by the affinity between the N element of the cyano group in the molecule and cobalt in the positive electrode, and can slow down the heat generation inside the electrochemical device under abuse conditions. When the positive electrode is over-lithiated, the polymer containing polyacrylonitrile functional groups can also capture Li + The over-lithiation is reduced.

[0021] The mass percentage of the first additive is 0.1% to 3% and the mass percentage of the second additive is 0.05% to 3% based on the mass of the positive electrode active material layer. The safety performance of the electrochemical device can be further improved and the electrochemical device has a higher energy density.

[0022] The negative electrode active material layer includes at least one of a third additive and a fourth additive. The third additive is a solid-state electrolyte, and the chemical coefficient of Li in the molecular formula of the solid-state electrolyte is less than 1, for example, La 0.5 Li 0.5 TiO3, Li 0.33 La 0.57 TiO3, Li 0.16 La 0.62 TiO3, Li 3x La (2 / 3-x)(1 / 3-2x) TiO3(0.03 < x < 0.167), La 0.55 Li 0.35 TiO3, La 0.55 Li 0.35 TiO3, La 0.6 Li 0.2 TiO3, La 0.63 Li 0.1 TiO3, La 0.55 Li 0.35 TiO3, La 0.57 Li 0.29 TiO3. When the chemical coefficient of Li in the molecular formula of the solid-state electrolyte in the negative electrode is less than 1, it can act as an additional lithium reservoir for fully charged graphite LiC6. The Li that tends to react with the electrolyte at high temperatures can be adsorbed and captured by the solid-state electrolyte, reducing the occurrence of side reactions. The fourth additive is a polymer containing polyacrylonitrile functional groups or sulfidized polyacrylonitrile. The polymer containing polyacrylonitrile and the sulfidized polyacrylonitrile can reduce the reaction between the negative electrode and the electrolyte by the affinity between the N and S elements of the cyano group in the molecule and Li in the negative electrode, and can slow down the heat generation inside the electrochemical device under abuse conditions.

[0023] The mass percentage of the third additive is 0.1% to 3% and the mass percentage of the fourth additive is 0.05% to 3% based on the mass of the negative active material layer. The safety performance of the electrochemical device can be further improved and the electrochemical device has a higher energy density.

[0024] In some embodiments, the mass average molecular weight Mw of the second additive and the fourth additive ranges from 3000 to 500000. The safety performance of the electrochemical device can be further improved.

[0025] In some embodiments, the ratio of the molar content of nitrogen element and carbon element N / C in the polymer containing polyacrylonitrile functional groups in the second additive and the fourth additive satisfies the following relationship: 0.03≤N / C<0.33. When the molar ratio of N / C is closer to 0.33, the proportion of polyacrylonitrile (PAN) in the polymer is closer to 100%, and when the molar ratio of N / C decreases, the proportion of polyacrylonitrile in the polymer decreases. By controlling the molar content ratio of N / C in the polymer containing polyacrylonitrile functional groups to be 0.03≤N / C<0.33, the electrochemical device has a higher energy density and improved safety performance.

[0026] In some embodiments, the polymer containing polyacrylonitrile functional groups comprises polyacrylonitrile and at least one of the following repeating units:

[0027] wherein n≥2. The polymer containing polyacrylonitrile functional groups contains PAA repeating units to improve the adhesion performance of the polymer, PEO repeating units to improve the ion conductivity of the polymer molecules, and PMMA repeating units to improve the flexibility of the polymer.

[0028] In some embodiments, in the fourth additive, the ratio of the molar content of nitrogen element and carbon element N / C and the ratio of the molar content of sulfur element and carbon element S / C in the sulfidized polyacrylonitrile satisfy the following relationship: 0.29≤N / C<0.33, 0.53<S / C<1.6. The higher the S / C ratio in the sulfidized polyacrylonitrile, the higher the relative content of sulfur in the sulfidized polyacrylonitrile, and the better the affinity for lithium ions at high temperatures. Under high-temperature abuse conditions, the heat generation reaction of the negative lithium ions and the electrolyte is more moderate, and the thermal runaway / overcharge pass rates of the battery are significantly improved. By controlling the molar content ratio of N / C in the sulfidized polyacrylonitrile to be 0.29≤N / C<0.33 and the molar content ratio of S / C to be 0.53<S / C<1.6, the electrochemical device has a higher energy density and improved safety performance.

[0029] In some embodiments, the sulfidized polyacrylonitrile comprises the following repeating unit:

[0030] The sulfurized polyacrylonitrile containing PAA repeating units is beneficial to improve the bonding performance.

[0031] In some embodiments, the mass percentage of sulfur in the sulfurized polyacrylonitrile is 20wt% to 60wt%. The safety performance of the electrochemical device can be further improved.

[0032] In some embodiments, the particle size distribution of the solid-state electrolyte in the first additive and the third additive satisfies the following relationship: the particle size Dv90 corresponding to 90% in the volume distribution is 0.1 μm to 10 μm, and the particle size Dv50 corresponding to 50% in the volume distribution is 0.1 μm to 1 μm. When the particle size Dv50 and Dv90 of the solid-state electrolyte are less than 1 μm and 10 μm respectively, the smaller Dv50 and Dv90 can achieve better coating of the positive and negative active materials by the solid-state electrolyte, thereby reducing the occurrence of high-temperature positive and negative side reactions. The oversized particles of the solid-state electrolyte can deteriorate the thermal box performance and overcharge performance. Therefore, by controlling the approximate particle size range of the solid-state electrolyte to satisfy the above range, the thermal box test / overcharge performance of the battery can be improved.

[0033] In some embodiments, the powder ionic conductivity of the solid-state electrolyte in the first additive and the third additive is greater than or equal to 10 -7 S / cm. When the powder ionic conductivity of the solid-state electrolyte is large, it is beneficial to the embedding and extraction of lithium ions at low temperature, thereby improving the low-temperature discharge performance of the battery.

[0034] The present application adds a specific positive electrode additive to the positive electrode and a specific negative electrode additive to the negative electrode, and the positive electrode additive and the negative electrode additive can interact with the lithium of the positive and negative electrodes, stabilize the reaction of the positive and negative electrodes at high temperature, and at the same time, through the hard combination of the solid-state electrolyte and the soft coating of the high molecular containing polyacrylonitrile functional group, the thermal stability of the positive and negative electrodes is improved. In addition, the molecules containing polyacrylonitrile functional group and the sulfurized polyacrylonitrile can interact with the cobalt of the positive electrode and the Li of the negative electrode through the N and S elements of the cyano group in the molecule, so that the reaction degree of the positive / negative electrode and the electrolyte is reduced, and the heat generation inside the electrochemical device under abuse conditions is slowed down. When the positive electrode is over-lithiated, the molecules containing polyacrylonitrile or the sulfurized polyacrylonitrile can also capture Li + to reduce over-lithiation. Therefore, when the thermal box test with high degree of delithiation or the overcharge test with over-lithiation is performed, the electrochemical device of the present application can obtain a higher test pass rate, and the thermal box test performance of the electrochemical device of the present application is improved at a high voltage of 4.45V or above. The electrochemical device of the present application has the characteristics of high energy density and good safety performance, and has good application prospect and value.

[0035] positive electrode

[0036] It is understood that the positive electrode active material layer includes, in addition to the additives described above, a positive electrode active material. The specific type of positive electrode active material is not particularly limited and can be selected as desired.

[0037] In some embodiments, the positive electrode active material includes a compound that reversibly intercalates and deintercalates lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive electrode active material can include a lithium transition metal complex oxide. The lithium transition metal complex oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material is selected from at least one of lithium cobaltate (LiCo02), lithium nickel manganese cobalt ternary material (NCM), lithium manganate (LiMn204), lithium nickel manganate (LiNi 0.5 Mn 1.5 04), lithium iron phosphate (LiFeP04), lithium nickel cobalt manganate, or lithium-rich manganese material.

[0038] In some embodiments, the positive electrode active material layer further includes a binder, and optionally, a conductive material. The binder can improve the cohesion of the positive electrode active material particles to each other and can improve the cohesion of the positive electrode active material to the positive electrode current collector. In some embodiments, the binder includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymeric ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, and nylon, among others.

[0039] In some embodiments, the positive electrode active material layer further includes a conductive material, thereby imparting electrical conductivity to the electrode. The conductive material can include any conductive material, so long as it does not cause chemical changes. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, etc.), metal-based materials (e.g., metal powders, metal fibers, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0040] In some embodiments, the positive electrode current collector is a metal, such as, for example, but not limited to, an aluminum foil.

[0041] In some embodiments, the structure of the positive electrode is a positive electrode structure known in the art that can be used in an electrochemical device.

[0042] In some embodiments, the method of preparing the positive electrode is a method of preparing a positive electrode for an electrochemical device known in the art. For example, the positive electrode can be obtained by mixing an active material, a conductive material, a binder, and the above-described positive electrode additive in a solvent to prepare a positive electrode active material slurry, and coating the positive electrode active material slurry on a current collector, drying, and cold-pressing to form a positive electrode active material layer. In some embodiments, the solvent can include water, N-methylpyrrolidone, etc., but is not limited thereto.

[0043] negative electrode

[0044] It can be understood that the negative electrode active material layer includes, in addition to the above-described additive, mainly a negative electrode active material. In some embodiments, the negative electrode active material includes a carbon material, a silicon-oxygen material, a silicon-carbon material. In some embodiments, the carbon material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, or hard carbon. In some embodiments, the negative electrode active material particles include at least one of natural graphite and artificial graphite. In some embodiments, the negative electrode active material particles can be graphite particles.

[0045] According to embodiments of the present application, the negative electrode active material particles can be obtained by selecting some low-volatile petroleum coke as a raw material, crushing it into single particles, and after being converted into graphite through heat treatment, performing surface modification treatment, and finally obtaining negative electrode active particles. Of course, the method of preparing the negative electrode active particles is not limited thereto, but other methods known in the art can also be used for preparation.

[0046] In some embodiments, the negative electrode active material layer further includes a binder. The binder can include various binder polymers such as polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene-styrene rubber, acrylated butadiene-styrene rubber, epoxy resin, nylon, etc.

[0047] In some embodiments, the negative electrode active material layer further includes a conductive agent to improve the conductivity of the electrode. Any electrically conductive material can be used as the conductive material as long as it does not cause chemical changes. Examples of the conductive agent include, but are not limited to, carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, etc.; metal-based materials such as metal powder or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives, etc.; or mixtures thereof.

[0048] In some embodiments, the negative current collector includes, but is not limited to, copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, polymer substrate coated with conductive metal, and any combination thereof. In some embodiments, the negative current collector is copper foil.

[0049] In some embodiments, the structure of the negative electrode is any structure known in the art that can be used in a negative electrode of an electrochemical device.

[0050] In some embodiments, the method of preparing the negative electrode is any method known in the art that can be used in a negative electrode of an electrochemical device. For example, the negative electrode can be prepared by mixing the active material, the conductive agent, the binder, and the above-mentioned negative electrode additives in a solvent, and heating the thickening agent as needed to prepare a negative electrode active material slurry, and coating the negative electrode active material slurry on a current collector, drying, and cold-pressing to form a negative electrode active material layer. In some embodiments, the solvent can include, but is not limited to, water, N-methylpyrrolidone.

[0051] electrolyte solution

[0052] The electrolyte used in the embodiments of the present application can be any electrolyte known in the art. The electrolyte can be classified into aqueous electrolyte and non-aqueous electrolyte, wherein the electrochemical device using the non-aqueous electrolyte can operate at a wider voltage window compared to the aqueous electrolyte, thereby achieving a higher energy density. In some embodiments, the non-aqueous electrolyte includes an organic solvent, an electrolyte, and an additive.

[0053] Electrolytes that can be used in the electrolyte of embodiments of the present application include, but are not limited to, inorganic lithium salts such as LiCIO4, LiAsF6, LiPF6, LiBF4, LiSbF6, LiSO3F, LiN(FSO2)2, and the like; fluorine-containing organic lithium salts such as LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,3-hexafluoropropanedisulfonimide lithium, cyclic 1,2-tetrafluoroethane disulfonimide lithium, LiPF4(CF3)2, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiPF4(CF3SO2)2, LiPF4(C2F5)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2; dicarboxylic acid complex-containing lithium salts such as lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, and the like. Additionally, the above electrolytes can be used singly, or two or more kinds can be used simultaneously. For example, in some embodiments, the electrolyte includes a combination of LiPF6and LiBF4. In some embodiments, the electrolyte includes LiPF6. In some embodiments, the mass percentage of the electrolyte is in the range of 8% to 15% based on the mass of the electrolyte.

[0054] The additive that can be used in the electrolyte of the present application can be any additive known in the art that can be used to improve the electrochemical performance of the battery. In some embodiments, the additive includes, but is not limited to, at least one of a polynitrile compound, a sulfur-containing additive, fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,4 butane sultone.

[0055] The organic solvent that can be used in the electrolyte of the present application can be any organic solvent known in the art. In some embodiments, the organic solvent includes, but is not limited to, a carbonate compound, an ester-based compound, an ether-based compound, a ketone-based compound, an alcohol-based compound, an aprotic solvent, or a combination thereof. Among them, examples of the carbonate compound include, but are not limited to, a chain carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof.

[0056] In some embodiments, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, methyl acetate, or ethyl propionate.

[0057] The preparation method of the electrolyte of the embodiments of the present application is not limited, and can be prepared in the conventional manner of electrolyte. In some embodiments, the electrolyte of the present application can be prepared by mixing the components.

[0058] separator film

[0059] In some embodiments, a separator is provided between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separator are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance formed of a material stable to the electrolyte of the present application, etc.

[0060] For example, in some embodiments, the separator includes a substrate layer. The substrate layer is a non-woven fabric, a film or a composite film having a porous structure. The material of the substrate layer can be selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, the material of the substrate layer can be selected from a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film.

[0061] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer can be a polymer layer, an inorganic layer or a layer formed by mixing a polymer and an inorganic substance. Specifically, the inorganic layer includes inorganic particles and a binder. The inorganic particles can be selected from one or a combination of several of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The binder can be selected from one or a combination of several of polyvinylidene fluoride, a polymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

[0062] The present application provides an electronic device including the above-described electrochemical device.

[0063] The use of the electrochemical device of the present application is not particularly limited, and it can be used in any electronic device known in the art. For example, the electronic device includes, but is not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copying machines, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, mini-disc players, transceivers, electronic organizers, calculators, memory cards, portable audio players, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting appliances, toys, game machines, timepieces, power tools, flashlights, cameras, home-use large storage batteries, and lithium-ion capacitors, etc. In addition, the electrochemical device of the present application is applicable not only to the above-mentioned electronic devices, but also to energy storage power stations, sea-borne vehicles, and air-borne vehicles. The air-borne vehicles include air-borne vehicles within the atmosphere and air-borne vehicles outside the atmosphere.

[0064] The technical solutions of the embodiments of the present application are further described below through specific examples.

[0065] Examples 1-17

[0066] I. Preparation of lithium-ion batteries

[0067] 1. Preparation of the negative electrode

[0068] The negative electrode active material (graphite particles), the conductive agent, the binder SBR, the thickening agent (sodium carboxymethyl cellulose, CMC), and the negative electrode additive were mixed in a solvent (deionized water), and stirred sufficiently to form a uniform negative electrode slurry. In each of Examples 1-17, the weight ratio of the negative electrode active material + negative electrode additive, the conductive agent, the binder, and the thickening agent was 96:1.5:1.5:1, and the specific weight percentage of the negative electrode additive is shown in Table 1. The negative electrode slurry was uniformly coated on a negative electrode current collector copper foil, dried, cold-pressed to form a negative electrode active material layer, and then cut and tabbed to obtain the negative electrode.

[0069] 2. Preparation of the positive electrode

[0070] The positive electrode active material (lithium iron phosphate), the conductive agent (acetylene black), the binder PVDF, and the positive electrode additive (e.g., Li7La3Zr2O 12) mixed in solvent N-methyl pyrrolidone (NMP) under vacuum stirring to obtain a positive electrode slurry. In each of Examples 1-17, the weight ratio of (positive electrode active material + positive electrode additive), conductive agent, and binder is 96.3:2.2:1.5, and the specific additive weight percentage of the positive electrode additive is shown in Table 1. The positive electrode slurry is coated on a positive electrode current collector aluminum foil, dried, cold-pressed to form a positive electrode active material layer, and then cut and tabbed to obtain a positive electrode. Taking Example 2 as an example, the second positive electrode additive type of 50% PAA + 50% PAN represents: the polymer contains 50% PAA repeating units and 50% PAN repeating units by weight percentage.

[0071] 3. Preparation of electrolyte

[0072] In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC:PC:EMC:DEC = 15:25:30:30, followed by the addition of 3% (mass percentage) of fluoroethylene carbonate and 2% (mass percentage) of 1,3-propane sultone. After dissolution and thorough stirring, lithium salt LiPF6 is added, and the mixture is uniformly mixed to obtain an electrolyte. The concentration of LiPF6 is 1 mol / L.

[0073] 4. Preparation of separator film

[0074] A porous polyethylene (PE) polymer film is used as the separator film.

[0075] 5. Preparation of lithium ion battery

[0076] The obtained positive electrode, separator film, and negative electrode are stacked in order, with the separator film between the positive electrode and the negative electrode to serve as a separator, and then wound to obtain a bare battery. The bare battery is placed in an outer packaging foil aluminum plastic film, electrolyte is injected, and then vacuum packaging, standing, and formation processes are performed to obtain a lithium ion battery.

[0077] The main difference between Examples 1-17 and Comparative Examples 1-2 is that the types and additive contents of the positive electrode additives and negative electrode additives used are different, as shown in Table 1. In Examples 1-17 and Comparative Examples 1-2, the first positive electrode additive has a Dv50 of 0.3±0.2 μm and a Dv90 of 0.9±0.2 μm, and the third negative electrode additive has a Dv50 of 0.4±0.2 μm and a Dv90 of 0.8±0.2 μm.

[0078] II. Test methods

[0079] 1. Determination of Li chemical coefficient in solid electrolyte molecular formula:

[0080] First, the basic type of solid electrolyte is determined by X-ray crystal diffraction test method, after determining the basic type, the solid electrolyte is digested, and the elements such as Li, Al, La and Ti contained in the solid electrolyte are determined as standard solution. After the content of Li and other elements in the solid electrolyte is determined by inductively coupled plasma spectroscopy (ICP), the chemical coefficient of Li is calculated.

[0081] 2. Determination of N / C, S / C:

[0082] The substance is put into the elemental analyzer, and the relative molar content of N, C and S elements is measured by the elemental analyzer. The ratio of the corresponding elements is obtained by the proportion of the relative content.

[0083] 3. Heat box test performance test of lithium ion battery

[0084] The heat box test process is shown as follows:

[0085] (1) Adjust the oven temperature to 25℃, and stand for 5min; (2) 0.2C DC to 3.0V;

[0086] (3) Stand for 10min; (4) 0.7C CC to 4.48V, CV to 0.025C;

[0087] (5) Stand for 10min.

[0088] Take a photo before testing, measure the voltage resistance, and paste the temperature sensing line on the surface of the battery. Put the sample into the heating oven box, and increase the temperature to 130±2℃ at a temperature increasing speed of 5±2℃ / min (the temperature can be changed to measure the difference, and the higher the temperature, the more difficult it is to pass) and keep for 60min. Take a photo after testing, measure the voltage resistance. If the battery does not catch fire and does not explode, it means that it passes the heat box test, and is recorded as P. 3P / 5T in Table 1 means that 3 batches of products in 5 batches of products pass the test, and 0P / 5T means that 0 batches of products in 5 batches of products pass the test.

[0089] 4. Overcharge performance test of lithium ion battery

[0090] The overcharge test process is shown as follows:

[0091] (1) Adjust the oven temperature to 25℃, and stand for 5min; (2) 0.2C DC to 3.0V;

[0092] (3) Stand for 10min.

[0093] Take a photo before the test, measure the voltage resistance, and paste the temperature-sensitive line on the surface of the battery. Put the sample into the overcharge test box, 0.5C CC to 4.48V, continue 0.5C CC for 3h, take a photo after the test, and measure the voltage resistance. If the battery does not catch fire or explode, it is considered to have passed the overcharge test, and is also marked as P.

[0094] III. Test Results

[0095] Table 1 lists the additive amounts of the positive and negative electrode sheets in Examples 1-17, and the positive and negative electrode sheets of Comparative Examples 1 and 2 do not add the above-mentioned additives, and the performance of the batteries corresponding to each example and comparative example. Among them, the full charge voltage of Comparative Example 1 and Examples 1-7 is 4.48V, and the full charge voltage of Comparative Example 2 and Examples 8-17 is 4.53V.

[0096] Table 1

[0097]

[0098]

[0099] From Table 1, it can be seen that the batteries of Examples 1 to 17 can at least guarantee the pass rate of the thermal box test at 130℃ 1h and 132℃ 1h, that is, the pass rate of the thermal box test of the batteries of Examples 1 to 17 at 130℃ 1h and 132℃ 1h all reaches 100%. This is because the solid-state electrolyte / containing polyacrylonitrile-based polymer coats the positive electrode material crystal and the negative electrode material surface, the solid-state electrolyte of the positive electrode stores the lithium of the negative electrode by supplementing lithium or receiving the solid-state electrolyte of the negative electrode, and the N element of the polyacrylonitrile-based polymer and the lithium of the negative electrode are reacted, the solid-state electrolyte produces hard coating, and the polyacrylonitrile polymer produces soft coating. This synergistic effect improves the high-temperature stability of the electrochemical device. The positive and negative electrodes of Comparative Examples 1 and 2 do not add the above-mentioned additives, so the thermal box test at 130℃ 1h cannot pass.

[0100] Examples 18-21

[0101] The preparation and performance test of the lithium ion batteries of Examples 18-21 are carried out according to Example 11, and the main difference from Example 11 is that the types and additive amounts of the positive electrode additives and negative electrode additives used are different, please refer to Table 2 for details.

[0102] Table 2 lists the additive types and contents of the positive and negative electrode sheets of Examples 18 to 21, the particle sizes of the positive first additive and the negative third additive material, and the corresponding hot box test and overcharge test results. The comparative example does not add any of the above positive and negative electrode additives as a comparison. In Table 2, NA represents that the positive / negative electrode does not add the corresponding additive and there is no corresponding information.

[0103] Table 2

[0104]

[0105] From Table 2, it can be seen that when the particle size Dv50 of the solid-state electrolyte is less than 1 μm and Dv90 is less than 10 μm, the hot box test performance and overcharge performance test are obviously improved. As can be seen from the comparison between Comparative Example 22 and Examples 21 and 19, smaller Dv50 and Dv90 can achieve better coating of the positive and negative active materials by the same solid-state electrolyte, thereby reducing the occurrence of high-temperature positive and negative electrode side reactions. Therefore, the hot box test / overcharge performance of the battery can be improved by controlling the approximate particle size range of the solid-state electrolyte.

[0106] Examples 23-27

[0107] The preparation and performance test of the lithium ion batteries of Examples 23-27 are carried out according to Example 9, and the main difference from Example 9 is that the material types and addition contents of the positive and negative electrode additives used are different. For details, please refer to Table 3.

[0108] Table 3 lists the performance parameters of the negative active material of Examples 23 to 27 and the corresponding battery performance. The comparative example does not add any of the above positive and negative electrode additives as a comparison. In Table 3, NA represents that the positive / negative electrode does not add the corresponding additive and there is no corresponding information.

[0109] Table 3

[0110]

[0111] As can be seen from Table 3, when the polyacrylonitrile functional group-containing polymer satisfies 0.03≤N / C<0.33, the hot box passing rate / overcharge passing rate of the battery is obviously improved. When the N / C molar ratio is closer to 0.33, the proportion of polyacrylonitrile (PAN) in the polymer is closer to 1, and the effect is the best. When the N / C molar ratio decreases, it means that the proportion of polyacrylonitrile in the polymer decreases, and the hot box / overcharge improvement effect will weaken, but it is still better than not adding polyacrylonitrile / vulcanized polyacrylonitrile.

[0112] As can be seen from Example 25 and Example 27, when the S / C is relatively high, it indicates that the relative content of sulfur in the vulcanized polyacrylonitrile is higher, the affinity for lithium ions at high temperature is better, the heat production reaction of the negative electrode lithium ions and the electrolyte is more moderate under high-temperature abuse conditions, and the thermal box passing / overcharge passing rate of the battery is obviously improved.

[0113] The above embodiments are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the present application.

Claims

1. An electrochemical device, comprising a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, and a negative electrode sheet including a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, characterized in that: the positive electrode active material layer includes at least one of a first additive that is a solid-state electrolyte having a chemical coefficient of Li in a molecular formula of the solid-state electrolyte greater than 0.5, and a second additive that is a polymer containing a polyacrylonitrile functional group, a mass percentage content of the first additive is 0.1% to 3% based on a mass of the positive electrode active material layer, and a mass percentage content of the second additive is 0.05% to 3% based on the mass of the positive electrode active material layer; the negative electrode active material layer includes at least one of a third additive that is a solid-state electrolyte having a chemical coefficient of Li in a molecular formula of the solid-state electrolyte less than 1, and a fourth additive that is a polymer containing a polyacrylonitrile functional group or a sulfidized polyacrylonitrile, a mass percentage content of the third additive is 0.1% to 3% based on a mass of the negative electrode active material layer, and a mass percentage content of the fourth additive is 0.05% to 3% based on the mass of the negative electrode active material layer; a mass average molecular weight Mw of the second additive and the fourth additive is in a range of 3,000 to 500,000; a ratio N / C of a molar content of nitrogen element to a molar content of carbon element in the polymer containing a polyacrylonitrile functional group in the second additive and the fourth additive satisfies a relationship of 0.03 ≤ N / C < 0.33; the polymer containing a polyacrylonitrile functional group includes at least one of the following repeating units: the sulfidized polyacrylonitrile in the fourth additive satisfies a relationship of 0.29 < N / C ≤ 0.33 and 0.53 < S / C < 1.6, in which N / C is a ratio of a molar content of nitrogen element to a molar content of carbon element, and S / C is a ratio of a molar content of sulfur element to a molar content of carbon element; a mass percentage of sulfur element in the sulfidized polyacrylonitrile is 20 wt% to 60 wt%; a particle size distribution of the solid-state electrolyte in the first additive and the third additive satisfies a relationship of Dv90 of 0.1 μm to 10 μm and Dv50 of 0.1 μm to 1 μm; and a voltage of the electrochemical device when the electrochemical device is fully charged is greater than or equal to 4.45 V. An electrochemical device according to any one of claims 1 to 10. ​ 2. The electrochemical device of claim 1, wherein ​ 3. The electrochemical device of claim 1, wherein ​ 4. The electrochemical device of claim 3, wherein ​ where n >

2.

5. The electrochemical device of claim 1, wherein ​ 6. The electrochemical device of claim 5, wherein, The sulfided polyacrylonitrile comprises the following repeat unit: wherein n >

2.

7. The electrochemical device of claim 1, wherein ​ 8. The electrochemical device of claim 1, wherein ​ 9. The electrochemical device of claim 1, wherein The powder ionic conductivity of the solid-state electrolyte in the first additive and the third additive is greater than or equal to 10 -7 S / cm.

10. The electrochemical device of claim 1, wherein ​ 11. An electronic device, comprising: ​

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