WO2024066339A1 - 锂离子电池以及包含其的电化学装置 - Google Patents

锂离子电池以及包含其的电化学装置 Download PDF

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WO2024066339A1
WO2024066339A1 PCT/CN2023/091190 CN2023091190W WO2024066339A1 WO 2024066339 A1 WO2024066339 A1 WO 2024066339A1 CN 2023091190 W CN2023091190 W CN 2023091190W WO 2024066339 A1 WO2024066339 A1 WO 2024066339A1
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Prior art keywords
ion battery
negative electrode
lithium
lithium ion
electrolyte
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PCT/CN2023/091190
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English (en)
French (fr)
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郑烨珍
周邵云
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宁德新能源科技有限公司
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Publication of WO2024066339A1 publication Critical patent/WO2024066339A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of electrochemical devices, and in particular to a lithium ion battery and an electrochemical device comprising the same.
  • secondary batteries such as lithium-ion secondary batteries
  • portable electronic devices such as mobile phones, laptops, and cameras due to their high energy density, high operating voltage, long cycle life, no memory effect, and green environmental protection.
  • Their scope of use is also expanding from small portable electronic devices to large electric transportation vehicles and renewable energy storage.
  • graphite-based negative electrode materials are the mainstream negative electrode materials for lithium-ion secondary batteries, which are mainly divided into artificial graphite and natural graphite.
  • Natural graphite has high capacity, high compaction density and relatively low price, but due to the different particle sizes, many surface defects, poor compatibility with electrolytes, more side reactions, and volume expansion during the cycle, resulting in increased internal stress of the battery, affecting the battery's service life and safety performance.
  • the present application provides a lithium ion battery and an electrochemical device comprising the lithium ion battery to improve the cycle performance and high temperature storage performance of the electrochemical device.
  • the present application provides a lithium-ion battery, which includes an electrolyte and a negative electrode plate, wherein the electrolyte includes vinyl carbonate and fluoroethylene carbonate, and the negative electrode plate includes a negative electrode active material, wherein the OI value of the negative electrode active material is a; based on the weight of the electrolyte, the weight percentage of vinyl carbonate is b%, and the weight percentage of fluoroethylene carbonate is c%; wherein a, b and c satisfy: 0.3 ⁇ a/(b+c) ⁇ 6, 0.02 ⁇ b+c ⁇ 10, 0.1 ⁇ b/c ⁇ 3.
  • the weight percentage of vinyl carbonate and the weight percentage of fluoroethylene carbonate satisfy a
  • the damage to the SEI film caused by the volume expansion of the negative electrode active material can be reduced, a tough SEI film can be formed on the negative electrode surface, the internal resistance of the lithium-ion battery can be significantly reduced, and the high-temperature storage performance and cycle performance of the lithium-ion battery can be improved.
  • the OI value of the negative electrode active material is a, and the range of a is: 2 ⁇ a ⁇ 15. In some embodiments, 3 ⁇ a ⁇ 7.
  • the weight percentage of vinylene carbonate is b% based on the weight of the electrolyte, and the range of b is: 0.01 ⁇ b ⁇ 10. In some embodiments, 0.1 ⁇ b ⁇ 5.
  • the weight percentage of fluoroethylene carbonate is c%, based on the weight of the electrolyte, and the range of c is: 0.01 ⁇ c ⁇ 10. In some embodiments, 0.1 ⁇ c ⁇ 5.
  • the negative electrode active material includes natural graphite.
  • the OI value of the negative electrode active material refers to the ratio of the peak area of the 004 characteristic diffraction peak in the X-ray diffraction spectrum of the negative electrode active material to the peak area of the 110 characteristic diffraction peak in the X-ray diffraction spectrum of the negative electrode active material.
  • the liquid retention coefficient of the lithium ion battery is e, and b, c and e satisfy: 0.01 ⁇ e ⁇ (b+c) ⁇ 50.
  • the liquid retention coefficient of the lithium ion battery is e that satisfies: 1 ⁇ e ⁇ 7.
  • the specific surface area of the negative electrode active material is f m 2 /g, and f is in the range of 1 ⁇ f ⁇ 3.
  • the electrolyte includes a compound B represented by formula (II):
  • the compound B represented by formula (II) includes at least one of the following: pyridine, 2-methylpyridine, 2-vinylpyridine, 2-ethynylpyridine, 2-fluoropyridine, 2-cyanopyridine, 3-vinylpyridine, 3-fluoropyridine, 2,6-difluoropyridine, pentafluoropyridine, 2,2'-bipyridine, terpyridine, 1,8-naphthyridine, 5,6,7,8-tetrahydroquinoline.
  • the compound B represented by formula (II) comprises at least one of the following: pyridine, 2-vinylpyridine, and 2-fluoropyridine.
  • the weight percentage of the compound represented by formula (II) is k%, and k satisfies: 0 ⁇ k ⁇ 3.
  • the Dv50 of the negative electrode active material is g ⁇ m, where g satisfies: 10 ⁇ g ⁇ 25.
  • the compaction density of the negative electrode active material is h g/cm 3 , and h satisfies: 1 ⁇ h ⁇ 1.8.
  • a second aspect of the present application provides an electrochemical device, which includes the lithium-ion battery provided in the first aspect of the present application.
  • the present application can reduce the problem of SEI film damage caused by volume expansion of the negative electrode active material and thus the deterioration of the cycle and storage performance caused by the expansion and gas production problems, and improve the cycle performance and high-temperature storage performance of the lithium-ion battery by setting the OI value of the negative electrode active material of the lithium-ion battery, the weight percentage of vinyl carbonate in the electrolyte, and the weight percentage of fluoroethylene carbonate in the electrolyte to satisfy a certain relationship.
  • the first aspect of the present application provides a lithium ion battery, which includes an electrolyte and a negative electrode plate, wherein the electrolyte includes vinylene carbonate and fluoroethylene carbonate, and the negative electrode plate includes a negative electrode active material, wherein the OI value of the negative electrode active material is a; based on the weight of the electrolyte, the weight percentage of vinylene carbonate is b%, and the weight percentage of fluoroethylene carbonate is b%.
  • the amount is c%; a, b and c satisfy: 0.3 ⁇ a/(b+c) ⁇ 6, 0.02 ⁇ b+c ⁇ 10, 0.1 ⁇ b/c ⁇ 3.
  • the compaction density is in a suitable range, the direction selectivity of natural graphite in the lithium insertion process is small, and the lithium insertion expansion can be dispersed in all directions, reducing the cycle expansion of the pole piece and the battery.
  • the SEI film formed by vinyl carbonate and fluoroethylene carbonate has a large impedance, an appropriate amount of additives should be added under the premise of ensuring performance; when the OI value of the negative electrode material is large, the cycle expansion of the pole piece and the battery is more serious, and the increase in the end face of the material leads to an increase in surface side reactions and worsening of gas production.
  • vinyl carbonate mainly generates PEO-type polymer SEI films
  • fluoroethylene carbonate mainly generates LiF and other inorganic SEI films.
  • the content of the two must meet the above relationship to form a SEI film rich in organic and inorganic components on the negative electrode surface.
  • the film has a certain toughness and elasticity, which can reduce the problems of cycle performance and storage performance caused by the destruction of the SEI film caused by the volume expansion of natural graphite.
  • the lithium-ion battery involved in the present application includes a positive electrode plate, a negative electrode plate, a separator, an electrolyte, etc., but is not limited thereto.
  • the lithium ion battery has better cycle performance and high temperature storage performance.
  • 0.2 ⁇ b+c ⁇ 5 and/or 0.5 ⁇ b/c ⁇ 2.5 When the content of vinylene carbonate and fluoroethylene carbonate meets the above, a SEI film rich in organic and inorganic components can be formed on the surface of the negative electrode, and the film has certain toughness and elasticity, which can reduce the damage of the SEI film caused by the volume expansion of natural graphite, so that the lithium-ion battery has better cycle performance and high-temperature storage performance.
  • the weight percentage of vinylene carbonate is b%, and the range of b is: 0.01 ⁇ b ⁇ 10, which can further improve the ion transport of the electrolyte and improve the battery performance. In some embodiments, 0.1 ⁇ b ⁇ 5.
  • the weight percentage of fluoroethylene carbonate is c%, and the range of c is: 0.01 ⁇ c ⁇ 10, which can improve the toughness of the negative electrode SEI film. In some embodiments, 0.1 ⁇ c ⁇ 5.
  • the liquid retention coefficient of the lithium ion battery is e, and b, c and e satisfy: 0.01 ⁇ e ⁇ (b+c) ⁇ 50.
  • a suitable electrolyte retention amount can further improve the ion transport in the electrolyte and improve the cycle performance of the battery.
  • the liquid retention coefficient e of the lithium ion battery satisfies: 1 ⁇ e ⁇ 7.
  • the electrolyte includes a compound B represented by formula (II):
  • the compound B represented by formula (II) includes at least one of the following: pyridine, 2-methylpyridine, 2-vinylpyridine, 2-ethynylpyridine, 2-fluoropyridine, 2-cyanopyridine, 3-vinylpyridine, 3-fluoropyridine, 2,6-difluoropyridine, pentafluoropyridine, 2,2'-bipyridine, terpyridine, 1,8-naphthyridine, 5,6,7,8-tetrahydroquinoline.
  • the compound B represented by formula (II) includes at least one of the following: pyridine, 2-vinylpyridine, 2-fluoropyridine.
  • the compound B represented by formula (II) can inhibit the consumption of solvents and film-forming additives during circulation and storage, thereby further improving the cycle performance.
  • the weight percentage of the compound represented by formula (II) is k%, and k satisfies: 0 ⁇ k ⁇ 3. In this case, the lithium-ion battery can have better cycle performance.
  • the electrolyte includes a lithium salt and an organic solvent.
  • the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt.
  • the lithium salt is selected from at least one of the following compounds: lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium difluorophosphate (LiPO 2 F 2 ), lithium bistrifluoromethanesulfonyl imide LiN(CF 3 SO 2 ) 2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO 2 F) 2 )(LiFSI), lithium bis(oxalatoborate) LiB(C 2 O 4 ) 2 (LiBOB) or lithium di(fluorooxalatoborate) LiBF 2 (C 2 O 4 )(LiDFOB).
  • the organic solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), carbon One or more of methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulf
  • the electrolyte may also optionally include additives.
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature performance, etc.
  • the negative electrode includes a negative electrode sheet, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the current collector, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes graphite, and the graphite includes at least one of natural graphite and artificial graphite.
  • the negative electrode active material is preferably natural graphite.
  • the OI value of the negative electrode active material is a: 2 ⁇ a ⁇ 15.
  • the cross-sectional proportion of the graphite material can be reduced, the side reaction can be reduced, and the cycle performance and high temperature storage performance of the lithium ion battery can be further improved.
  • the specific surface area of the negative electrode active material is f m 2 /g, and the range of f is: 1 ⁇ f ⁇ 3.
  • the specific surface area of the negative electrode active material is within this range, which can ensure contact with the electrolyte and has less side reactions with the electrolyte, further improving the cycle performance of the battery.
  • the Dv50 of the negative electrode active material is g ⁇ m, where g satisfies: 10 ⁇ g ⁇ 25.
  • the compaction density of the negative electrode active material is h g/cm 3 , and h satisfies: 1 ⁇ h ⁇ 1.8.
  • the negative electrode active material may also include one or more of mesophase microcarbon beads (MCMB for short), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO 2 , spinel-structured lithiated TiO 2 -Li 4 Ti 5 O 12 , and Li-Al alloy, but is not limited thereto.
  • MCMB mesophase microcarbon beads
  • the negative electrode active material layer may include a binder and optionally a conductive material.
  • the binder improves the bonding of the negative electrode active material particles to each other and to the current collector.
  • non-limiting examples of binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.
  • non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, Artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives) and mixtures thereof.
  • carbon-based materials e.g., natural graphite, Artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.
  • metal-based materials e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.
  • conductive polymers e.g., polyphenylene derivatives
  • the negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal.
  • the negative electrode active material is natural graphite
  • the conductive agent is Super P
  • the binder is polyvinylidene fluoride (PVDF).
  • the positive electrode includes a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active material layer disposed on the current collector.
  • the positive electrode active material includes a compound that reversibly embeds and deintercalates lithium ions.
  • the positive electrode active material may include a composite oxide containing lithium and at least one element selected from cobalt, manganese and nickel.
  • the specific types of positive electrode active materials are not subject to specific restrictions and can be selected according to needs.
  • the positive electrode active material is selected from at least one of lithium cobalt oxide LiCoO 2 (LCO), lithium nickel manganese cobalt ternary material (NCM), lithium iron phosphate, and lithium manganese oxide. They can be used alone or in any combination of two or more.
  • the positive electrode active material may have a coating on the surface.
  • the compound for the coating may be amorphous or crystalline, and the coating element contained in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof.
  • the coating may be applied by any method as long as the method does not adversely affect the performance of the positive electrode active material.
  • the method may include any coating method well known to those of ordinary skill in the art, such as spraying, dipping, etc.
  • the positive electrode active material layer further includes a binder, and optionally a conductive material.
  • the binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector.
  • non-limiting examples of binders include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, and the like.
  • non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.
  • carbon-based materials e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.
  • metal-based materials e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.
  • conductive polymers e.g., polyphenylene derivatives
  • the positive electrode current collector may be aluminum foil (Al), but is not limited thereto.
  • the positive electrode active material is LiFePO 4
  • the conductive agent is Super P
  • the binder is polyvinylidene fluoride (PVDF).
  • the electrochemical device is provided with a separator between the positive electrode and the negative electrode to prevent short circuit.
  • the material and shape of the separator used in the electrochemical device are not particularly limited, and it can be any technology disclosed in the prior art.
  • the diaphragm may include a substrate layer and a surface treatment layer.
  • the substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide.
  • polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite film can be selected.
  • a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance.
  • the inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from one or more combinations 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 and barium sulfate.
  • the adhesive is selected from one or a combination of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
  • the polymer layer contains a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene).
  • the lithium-ion battery involved in the present application is made by stacking the above-mentioned positive and negative electrode sheets.
  • the lithium-ion battery involved in the present application may include an outer packaging, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package.
  • the material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.
  • the present application also provides a battery module.
  • the battery module includes the above-mentioned lithium-ion battery.
  • the battery module uses the above-mentioned lithium-ion battery, and therefore has at least the same advantages as the lithium-ion battery.
  • the number of lithium-ion batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • the present application further provides a battery pack, which includes the above-mentioned battery module.
  • the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • the second aspect of the present application provides an electrochemical device, which includes the lithium-ion battery described in the first aspect of the present application.
  • the electrochemical device includes, but is not limited to: an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, a power storage system, etc.
  • a battery pack or a battery module can be used.
  • the electrochemical device can be a hand Computers, tablet computers, notebook computers, etc.
  • the electrochemical device is usually required to be thin and light, and a lithium-ion battery can be used as a power source.
  • the positive electrode active material LiFePO 4 , the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) are mixed in a solvent N-methylpyrrolidone (NMP) at a weight ratio of about 96:2:2, and stirred evenly to obtain a slurry.
  • NMP solvent N-methylpyrrolidone
  • the slurry is coated on the positive electrode current collector aluminum foil, dried and cold pressed to obtain a positive electrode active material layer, and then cut, slit, and welded to the tab to obtain the positive electrode.
  • Natural graphite with different OI values, conductive agent Super P, and thickener sodium carboxymethyl cellulose are fully stirred and mixed in an appropriate amount of deionized water solvent at a weight ratio of 95:2:3 to form a uniform negative electrode slurry.
  • the slurry is coated on the negative electrode current collector copper foil, dried and cold pressed to obtain the negative electrode active material layer, and then cut, slit, and weld the pole ears to obtain the negative electrode.
  • Examples 1-30 and Comparative Examples 1-3 In an argon atmosphere glove box with a water content of ⁇ 10ppm, a certain amount of organic solvents ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed evenly, and fully dried lithium salt LiPF 6 is dissolved in the above organic solvent to obtain an electrolyte. Among them, the weight percentage of lithium salt LiPF 6 is 12.5%, the weight percentage of ethylene carbonate (EC) is 26%, and the rest is DEC (the content of each substance in the electrolyte is calculated based on the weight of the electrolyte). Add vinylene carbonate and fluoroethylene carbonate in the amounts shown in Table 1 to the electrolyte.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • Examples 31-44 and Comparative Example 4-3 In an argon atmosphere glove box with a water content of ⁇ 10ppm, a certain amount of organic solvents ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed evenly, and fully dried lithium salt LiPF 6 was dissolved in the above non-aqueous solvent to obtain an electrolyte, wherein the weight percentage of lithium salt LiPF 6 was 12.5%, the weight percentage of EC was 26%, the weight percentage of VC was 2.5%, the weight percentage of FEC was 1%, and the rest was DEC. Compound B was added to the electrolyte in the amount shown in Table 2.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • a polyethylene (PE) porous film is used as the isolation membrane, and the porosity is 35%.
  • the positive electrode, the separator, and the negative electrode are stacked in order, so that the separator is between the positive electrode and the negative electrode to play an isolating role, and then they are wound to obtain a bare cell; the bare cell is placed in an outer packaging foil aluminum-plastic film, and the prepared electrolyte is injected into the dried bare cell. After vacuum packaging, standing, formation, shaping, capacity testing and other processes, the preparation of the lithium-ion battery is completed.
  • Normal temperature cycle performance test Place the finished lithium-ion battery of the above embodiment and comparative example in a 25°C constant temperature box and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge the lithium-ion battery that has reached a constant temperature at a constant current of 1C to a voltage of 3.6V, then charge at a constant voltage of 3.6V to a current less than or equal to 0.05C, and then discharge at a constant current of 1C to a voltage of 2.8V. This is a charge and discharge cycle, and the thickness of the battery cell is tested at the same time. Take the capacity of the first discharge as 100%, repeat the charge and discharge cycle 1000 times, stop the test, and record the corresponding discharge capacity. The calculation formula for the capacity retention rate is as follows:
  • Capacity retention rate (discharge capacity after cycle/first discharge capacity) ⁇ 100%.
  • Cyclic expansion rate test of negative electrode sheet The thickness of the negative electrode after cold pressing is recorded as H 0 , and the battery cell is fully charged after 1000 cycles, the battery is disassembled and the thickness of the corresponding negative electrode sheet is tested, recorded as H 1 .
  • the finished lithium-ion batteries of the above embodiments and comparative examples were placed in a constant temperature box at 25°C for 5 minutes, charged to 3.6V at a constant current rate of 1C, and then charged at a constant voltage until the current was less than or equal to 0.05C, and then placed for 5 minutes, discharged to 2.8V at a constant current rate of 1C, and then charged to 3.6V at a constant current rate of 1C, and charged at a constant voltage until the current was less than or equal to 0.05C, and then the fully charged lithium-ion secondary battery was placed in a 60°C oven for 90 days. After 90 days of storage, the lithium-ion battery was taken out and its thickness change was observed and recorded.
  • the calculation formula of the thickness growth rate is as follows:
  • Thickness increase rate (thickness after high-temperature storage-thickness before high-temperature storage)/thickness before high-temperature storage ⁇ 100%.
  • Lithium-ion secondary battery DC impedance test (DCR test):
  • the finished lithium-ion batteries of the above embodiments and comparative examples were placed in a thermostat at 25°C for 5 minutes, charged to 3.6V at a constant current rate of 1C, then charged to a current of less than or equal to 0.05C at a constant voltage, left to stand for 30 minutes, discharged at a current of 0.1C for 10 seconds (taking a point every 0.1 seconds, and recording the corresponding voltage value U 1 ), and discharged at a current of 1C for 360 seconds (taking a point every 0.1 seconds, and recording the corresponding voltage value U 2 ).
  • the charging and discharging steps were repeated 5 times.
  • “1C” is the current value that completely discharges the battery capacity within 1 hour.
  • the obtained DCR is The concentration polarization impedance of the present application is a value at 50% SOC (ie, state of charge), ie, 50% SOC DCR in the embodiment, and the unit is milliohm.
  • the OI value is tested by an X-ray diffractometer (such as a Bruker D8 Discover X-ray diffractometer), and JISK 0131-1996 can be referred to.
  • the specific surface area BET of the negative electrode can be tested by methods known in the art. For example, it can be tested by nitrogen adsorption specific surface area analysis test method with reference to GB/T19587-2017, and calculated by BET (Brunauer Emment Teller) method, wherein the nitrogen adsorption specific surface area analysis test can be tested by Tri-Star 3020 specific surface area pore size analysis tester of Micromeritics, USA.
  • disassemble the battery described in the embodiment and comparative example soak the disassembled negative electrode sheet in a dispersant so that the negative electrode material is dispersed in the dispersant (ethanol), and then ultrasonically apply for 30 minutes, put the obtained material into a vacuum drying oven for drying, and finally use a specific surface area tester to measure the specific surface area of the negative electrode material.
  • a dispersant ethanol
  • the Dv50 value of the negative electrode active material can be measured by using a laser particle size analyzer (such as Malvern Master Size 300) with reference to the standard GB/T 19077.1-2016.
  • Dv50 represents the particle size corresponding to when the cumulative volume distribution percentage of the negative electrode active material reaches 50%.
  • the prepared lithium-ion battery was tested according to the above test method.
  • the test results are shown in Table 1 and Table 2.
  • the compaction density of the negative electrode is within the appropriate range.
  • the direction selectivity of natural graphite in the lithium insertion process is small, and the lithium insertion expansion can be dispersed in all directions, reducing the cycle expansion of the electrode and the battery.
  • the SEI film formed by esters has a large impedance, so an appropriate amount of additives should be added under the premise of ensuring performance; when the OI value of the negative electrode material is large, the cycle expansion of the pole piece and the battery is more serious, and the increase in the end faces of the material will lead to an increase in surface side reactions and worse gas production. At this time, more vinylene carbonate and fluoroethylene carbonate are needed to protect the negative electrode material and improve the expansion and gas production problems.
  • the lithium-ion battery has better cycle performance and low impedance; in addition, vinylene carbonate mainly generates PEO type polymer SEI film, and fluoroethylene carbonate mainly generates LiF and other inorganic SEI films.
  • the content of the two must meet 0.01 ⁇ b+c ⁇ 10 and 0.5 ⁇ b/c ⁇ 2.5 to form a SEI film rich in organic and inorganic components on the negative electrode surface.
  • the film has certain toughness and elasticity, which can reduce a series of problems such as the deterioration of the cycle and storage performance caused by the damage of the SEI film caused by the volume expansion of natural graphite; and the appropriate electrolyte retention can improve the cycle performance of the battery.
  • the nitrogen-containing heterocyclic compound can form a stable SEI film on the surface of the negative electrode, inhibiting the consumption of solvents and other film-forming additives during the cycle and storage process; in addition, the nitrogen-containing cation part of the nitrogen-containing heterocyclic compound B represented by formula (II) can not only promote the dissociation of lithium salts, but also complex with Lewis bases such as ethylene carbonate (EC), thereby improving the oxidation stability of EC electrolyte.
  • EC ethylene carbonate
  • the nitrogen-containing heterocyclic compound B represented by formula (II) can be appropriately added to achieve the best performance.

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Abstract

本申请涉及一种锂离子电池以及包含其的电化学装置，锂离子电池包括电解液和负极极片，电解液包括碳酸亚乙烯酯和氟代碳酸乙烯酯；负极极片包括负极活性材料，并且负极活性材料的OI值为a；基于电解液的重量，碳酸亚乙烯酯的重量百分含量为b％，氟代碳酸乙烯酯的重量百分含量为c％；a、b和c满足：0.3≤a/(b+c)≤6，0.02≤b+c≤10，0.1＜b/c＜3。当负极活性材料的OI值、碳酸亚乙烯酯的重量百分含量和氟代碳酸乙烯酯的重量百分含量满足上述关系式时，可以减少因为负极活性材料体积膨胀带来的SEI膜破坏，且在负极表面形成具有韧性的SEI膜，显著降低锂离子电池内阻以及改善锂离子电池的高温存储性能及循环性能。

Description

锂离子电池以及包含其的电化学装置
本申请要求于2022年9月30日提交的名称为“锂离子电池以及包含其的电化学装置”的中国专利申请202211211360.7的优先权，该申请的全部内容通过引用包含在本申请中。
技术领域
本申请涉及电化学装置技术领域，尤其涉及一种锂离子电池以及包含其的电化学装置。
背景技术
二次电池(例如锂离子二次电池)作为一种新型的可移动储能装置，由于具有高能量密度、高工作电压、循环寿命长、无记忆效应、绿色环保等特点，迄今已经在手机、笔记本电脑、摄像机等便携式电子设备领域得到了广泛的应用，其使用范围也正从小型便携式电子设备向大型电动运输工具和可再生能源存储领域扩展。
目前石墨类的负极材料为主流的锂离子二次电池用负极材料，主要分为人造石墨以及天然石墨。天然石墨的容量高，压实密度高，价格也比较便宜，但是由于颗粒大小不一，表面缺陷较多，与电解液的相容性比较差，副反应比较多，并且在循环过程中会发生体积膨胀，导致电池的内应力增大，影响电池的使用寿命和安全性能。
发明内容
针对现有技术中存在的问题，本申请提供了一种锂离子电池以及包含该锂离子电池的电化学装置，以提升电化学装置的循环性能和高温存储性能。
本申请第一方面提供了一种锂离子电池，其包括电解液和负极极片，电解液包括碳酸亚乙烯酯和氟代碳酸乙烯酯，负极极片包括负极活性材料，负极活性材料的OI值为a；基于电解液的重量，碳酸亚乙烯酯的重量百分含量为b％，氟代碳酸乙烯酯的重量百分含量为c％；所述a、b和c满足：0.3≤a/(b+c)≤6，0.02≤b+c≤10，0.1＜b/c＜3。当负极活性材料的OI值、碳酸亚乙烯酯的重量百分含量和氟代碳酸乙烯酯的重量百分含量满足一 定的关系式时，可以减少因为负极活性材料体积膨胀带来的SEI膜破坏，在负极表面形成具有韧性的SEI膜，显著降低锂离子电池内阻以及改善锂离子电池的高温存储性能及循环性能。
在一些实施方式中，0.4≤a/(b+c)≤3。
在一些实施方式中，0.2≤b+c≤5。
在一些实施方式中，0.5≤b/c≤2.5。
在一些实施方式中，负极活性材料的OI值为a，a的范围为：2≤a≤15。在一些实施方式中，3≤a≤7。
在一些实施方式中，基于电解液的重量，碳酸亚乙烯酯的重量百分含量为b％，b的范围为：0.01≤b≤10。在一些实施方式中，0.1≤b≤5。
在一些实施方式中，基于电解液的重量，氟代碳酸乙烯酯的重量百分含量为c％，c的范围为：0.01≤c≤10。在一些实施方式中，0.1≤c≤5。
在一些实施方式中，负极活性材料包括天然石墨。负极活性材料的OI值是指OI值为负极活性材料的X射线衍射图谱中004特征衍射峰的峰面积与负极活性材料的X射线衍射图谱中110特征衍射峰的峰面积的比值。
在一些实施方式中，锂离子电池的保液系数为e，b、c和e满足：0.01≤e×(b+c)≤50。
在一些实施方式中，锂离子电池的保液系数为e满足：1≤e≤7。
在一些实施方式中，负极活性材料的比表面积为f m2/g，f的范围为：1≤f≤3。
在一些实施方式中，电解液包括式(II)所表示的化合物B：
其中:
R6、R7、R8、R9和R10各自独立地选自氢、氰基、卤素原子、C1-10烷基、C2-10烯基、 C2-10炔基、C3-6杂环基、C5-6芳基、C5-6杂芳基、-R11-(C＝O)-R12-、-R11-(C＝O)-O-R12-、-R11-(C＝O)-NH-R12-、或者R6、R7、R8、R9和R10中任意相邻的两者相互连接以形成C1-10的环状结构；其中，R11和R12各自独立地选自单键、C1-10烷基、C2-10烯基、C2-10炔基、C3-6杂环基、C5-6芳基或C5-6杂芳基；所述C1-10烷基、C2-10烯基、C2-10炔基、C3-6杂环基、C5-6芳基、C5-6杂芳基或C1-10的环状结构任选地被一个或更多个氨基、氰基、卤素原子、C1-3烷基、C3-6杂环基、C5-6杂芳基所取代。
在一些实施方式中，式(II)所表示的化合物B包括以下中的至少一者：吡啶、2-甲基吡啶、2-乙烯基吡啶、2-乙炔基吡啶、2-氟吡啶、2-氰基吡啶、3-乙烯基吡啶，3-氟吡啶、2,6-二氟吡啶、五氟吡啶、2,2'-联吡啶、三联吡啶、1,8-萘啶、5,6,7,8-四氢喹啉。
在一些实施方式中，式(II)所表示的化合物B包括以下中的至少一者：吡啶、2-乙烯基吡啶、2-氟吡啶。
在一些实施方式中，基于所述电解液的重量，所述式(II)所表示的化合物的重量百分含量为k％，k满足：0≤k＜3。
在一些实施方式中，负极活性材料的Dv50为gμm，g满足：10≤g≤25。
在一些实施方式中，负极活性材料的压实密度为h g/cm3，h满足：1≤h≤1.8。
本申请第二方面提供了一种电化学装置，其包括本申请第一方面提供的锂离子电池。
本申请通过设置锂离子电池的负极活性材料的OI值、电解液中碳酸亚乙烯酯的重量百分含量、电解液中氟代碳酸乙烯酯的重量百分含量满足一定的关系式时，可以减少因为负极活性材料体积膨胀带来的SEI膜破坏进而引起的循环和存储性能恶化的问题，并且可以改善膨胀及产气问题，提升锂离子电池的循环性能和高温存储性能。
具体实施方式
为使本申请的目的、技术方案和优点更加清楚，下面将结合实施例对本申请的技术方案进行清楚、完整地描述，显然，所描述的实施例是本申请一部分实施例，而不是全部的实施例。在此所描述的有关实施例为说明性质的且用于提供对本申请的基本理解。本申请的实施例不应该被解释为对本申请的限制。
本申请第一方面提供了一种锂离子电池，其包括电解液和负极极片，电解液包括碳酸亚乙烯酯和氟代碳酸乙烯酯，负极极片包括负极活性材料，负极活性材料的OI值为a；基于电解液的重量，碳酸亚乙烯酯的重量百分含量为b％，氟代碳酸乙烯酯的重量百分含 量为c％；所述a、b和c满足：0.3≤a/(b+c)≤6，0.02≤b+c≤10，0.1＜b/c＜3。
在本申请内容中，当负极活性材料的OI值较小时，压实密度在合适范围，天然石墨在嵌锂过程中的方向选择性较小，嵌锂膨胀可被分散到各个方向，降低极片和电池的循环膨胀，由于碳酸亚乙烯酯和氟代碳酸乙烯酯所形成的SEI膜阻抗较大，因此在保证性能的前提下应适量的添加添加剂；当负极材料的OI值较大时，极片和电池的循环膨胀较严重，且材料端面变多导致表面副反应会增多，产气恶化，这时需要更多的碳酸亚乙烯酯和氟代碳酸乙烯酯对负极材料进行保护，改善膨胀及产气问题。在本申请内容中，碳酸亚乙烯酯主要生成PEO型聚合物SEI膜，氟代碳酸乙烯酯主要生成LiF等含无机成分SEI膜，两者含量要满足以上关系才能在负极表面形成富含有机和无机成分的SEI膜，该膜具有一定的韧性和弹性，能够减少因为天然石墨体积膨胀带来的SEI膜破坏进而引起的循环性能和存储性能方面的问题。
在一些实施方式中，本申请涉及的锂离子电池包含正极极片、负极极片、隔膜、电解液等，但不限于此。
电解液：
在一些实施方式中，0.4≤a/(b+c)≤3。碳酸亚乙烯酯和氟代碳酸乙烯酯的含量和负极材料的OI值在此范围内时，使锂离子电池具有更优循环性能和高温存储性能。
在一些实施方式中，0.2≤b+c≤5和/或0.5≤b/c≤2.5。碳酸亚乙烯酯和氟代碳酸乙烯酯的含量满足上述时，能在负极表面形成富含有机和无机成分的SEI膜，该膜具有一定的韧性和弹性，能够减少因为天然石墨体积膨胀带来的SEI膜破坏，使锂离子电池具有更优循环性能和高温存储性能。
在一些实施方式中，基于电解液的重量，碳酸亚乙烯酯的重量百分含量为b％，b的范围为：0.01≤b≤10，可进一步改善电解液的离子传输，改善电池性能。在一些实施方式中，0.1≤b≤5。
在一些实施方式中，基于电解液的重量，氟代碳酸乙烯酯的重量百分含量为c％，c的范围为：0.01≤c≤10，可改善负极SEI膜的韧性，在一些实施方式中，0.1≤c≤5。
在一些实施方式中，锂离子电池的保液系数为e，b、c和e满足：0.01≤e×(b+c)≤50。合适的电解液保有量可以进一步改善电解液的中的离子传输，提高电池的循环性能。在一些实施方式中，锂离子电池的保液系数e满足：1≤e≤7。
在一些实施方式中，电解液包括式(II)所表示的化合物B：
其中:
R6、R7、R8、R9和R10各自独立地选自氢、氰基、卤素原子、C1-10烷基、C2-10烯基、C2-10炔基、C3-6杂环基、C5-6芳基、C5-6杂芳基、-R11-(C＝O)-R12-、-R11-(C＝O)-O-R12-、-R11-(C＝O)-NH-R12-、或者R6、R7、R8、R9和R10中任意相邻的两者相互连接以形成C1-10的环状结构；其中，R11和R12各自独立地选自单键、C1-10烷基、C2-10烯基、C2-10炔基、C3-6杂环基、C5-6芳基或C5-6杂芳基；所述C1-10烷基、C2-10烯基、C2-10炔基、C3-6杂环基、C5-6芳基、C5-6杂芳基或C1-10的环状结构任选地被一个或更多个氨基、氰基、卤素原子、C1-3烷基、C3-6杂环基、C5-6杂芳基所取代。
在一些实施方式中，式(II)所表示的化合物B包括以下中的至少一者：吡啶、2-甲基吡啶、2-乙烯基吡啶、2-乙炔基吡啶、2-氟吡啶、2-氰基吡啶、3-乙烯基吡啶，3-氟吡啶、2,6-二氟吡啶、五氟吡啶、2,2'-联吡啶、三联吡啶、1,8-萘啶、5,6,7,8-四氢喹啉。
在一些实施方式中，式(II)所表示的化合物B包括以下中的至少一者：吡啶、2-乙烯基吡啶、2-氟吡啶。式(II)所表示的化合物B可以抑制循环和存储过程中溶剂和成膜添加剂的消耗，从而进一步提高循环性能。
在一些实施方式中，基于所述电解液的重量，所述式(II)所表示的化合物的重量百分含量为k％，k满足：0≤k＜3。此时可使锂离子电池具有更优的循环性能。
在一些实施方式中，电解液包括锂盐和有机溶剂。
在一些实施方式中，锂盐包括有机锂盐或无机锂盐中的至少一种。在一些实施方式中，所述锂盐选自以下化合物中至少一者：六氟磷酸锂(LiPF6)、四氟硼酸锂(LiBF4)、二氟磷酸锂(LiPO2F2)、双三氟甲烷磺酰亚胺锂LiN(CF3SO2)2(LiTFSI)、双(氟磺酰)亚胺锂Li(N(SO2F)2)(LiFSI)、双草酸硼酸锂LiB(C2O4)2(LiBOB)或二氟草酸硼酸锂LiBF2(C2O4)(LiDFOB)。
在一些实施方式中，有机溶剂可选自碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳 酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的一种或几种。
在一些实施方式中，电解液中还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温性能的添加剂等。
负极：
在一些实施方式中，负极包括负极极片，负极极片包括负极集流体和设置在集流体上的负极活性材料层，负极活性材料层包括负极活性材料。负极活性材料包括石墨，石墨包括天然石墨或人造石墨中的至少一种。
在一些实施方式中，负极活性材料优选为天然石墨。
在一些实施方式中，负极活性材料的OI值为a：2≤a≤15。负极材料的OI值在此范围内时，可减少石墨材料断面占比，减少副反应，进一步改善锂离子电池的循环性能和高温存储性能。在一些实施方式中，3≤a≤7。
在一些实施方式中，负极活性材料的比表面积为f m2/g，f的范围为：1≤f≤3。负极活性材料的比表面积在此范围内，可保证与电解液的接触，且与电解液间的副反应较少，进一步提高电池的循环性能。
在一些实施方式中，负极活性材料的Dv50为gμm，g满足：10≤g≤25。
在一些实施方式中，负极活性材料的压实密度为h g/cm3，h满足：1≤h≤1.8。
在一些实施方式中，负极活性材料还可以包括中间相微碳球(简称为MCMB)、硬碳、软碳、硅、硅-碳复合物、Li-Sn合金、Li-Sn-O合金、Sn、SnO、SnO2、尖晶石结构的锂化TiO2-Li4Ti5O12、Li-Al合金中的一种或几种，但不限于此。
在一些实施方式中，负极活性材料层可以包括粘合剂，并且可选地还包括导电材料。粘合剂提高负极活性材料颗粒彼此间的结合和负极活性材料与集流体的结合。
在一些实施方式中，粘合剂的非限制性示例包括聚乙烯醇、羧甲基纤维素、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚四氟乙烯、聚偏1,1-二氟乙烯、聚乙烯、聚丙烯、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂、尼龙等。
在一些实施方式中，导电材料的非限制性示例包括基于碳的材料(例如，天然石墨、 人造石墨、碳黑、乙炔黑、科琴黑、碳纤维等)、基于金属的材料(例如，金属粉、金属纤维等，例如铜、镍、铝、银等)、导电聚合物(例如，聚亚苯基衍生物)和它们的混合物。
在一些实施方式中，负极集流体可以选自铜箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜或覆有导电金属的聚合物基底。
在一些实施方式中，负极活性材料为天然石墨，导电剂为Super P，粘合剂为聚偏二氟乙烯(PVDF)。
正极：
在一些实施方式中，正极包括正极极片，正极极片包括正极集流体和设置在集流体上的正极活性材料层。正极活性材料包括可逆地嵌入和脱嵌锂离子的化合物。正极活性材料可以包括复合氧化物，该复合氧化物含有锂以及从钴、锰和镍中选择的至少一种元素。正极活性材料的具体种类均不受到具体的限制，可根据需求进行选择。正极活性材料任选自钴酸锂LiCoO2(LCO)、锂镍锰钴三元材料(NCM)、磷酸铁锂、锰酸锂中的至少一种。它们可以单独使用1种，也可以任何组合并用2种以及2种以上。
在一些实施方式中，正极活性材料可以在表面上具有涂层。用于涂层的化合物可以是非晶的或结晶的，在涂层中含有的涂覆元素可以包括Mg、Al、Co、K、Na、Ca、Si、Ti、V、Sn、Ge、Ga、B、As、Zr或它们的混合物。可以通过任何方法来施加涂层，只要该方法不对正极活性材料的性能产生不利影响即可。例如，该方法可以包括对本领域普通技术人员来说众所周知的任何涂覆方法，例如喷涂、浸渍等。
在一些实施方式中，正极活性材料层还包括粘合剂，并且可选地还包括导电材料。粘合剂提高正极活性材料颗粒彼此间的结合，并且还提高正极活性材料与集流体的结合。
在一些实施方式中，粘合剂的非限制性示例包括聚乙烯醇、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚四氟乙烯、聚偏1,1-二氟乙烯、聚乙烯、聚丙烯、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂、尼龙等。
在一些实施方式中，导电材料的非限制性示例包括基于碳的材料(例如，天然石墨、人造石墨、碳黑、乙炔黑、科琴黑、碳纤维等)、基于金属的材料(例如，金属粉、金属纤维等，包括例如铜、镍、铝、银等)、导电聚合物(例如，聚亚苯基衍生物)和它们的混合物。
在一些实施方式中，正极集流体可以是铝箔(Al)，但不限于此。
在一些实施方式中，正极活性材料为LiFePO4，导电剂为Super P，粘合剂为聚偏二氟乙烯(PVDF)。
隔膜：
在一些实施例中，电化学装置在正极与负极之间设有隔膜以防止短路。电化学装置中使用的隔膜的材料和形状没有特别限制，其可为任何现有技术中公开的技术。
在一些实施例中，隔膜可包括基材层和表面处理层。基材层为具有多孔结构的无纺布、膜或复合膜，基材层的材料选自聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯和聚酰亚胺中的至少一种。具体的，可选用聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。无机物层包括无机颗粒和粘合剂，无机颗粒选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙和硫酸钡中的一种或几种的组合。粘合剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯和聚六氟丙烯中的一种或几种的组合。聚合物层中包含聚合物，聚合物的材料选自聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚偏氟乙烯、聚(偏氟乙烯-六氟丙烯)中的至少一种。
在一些实施方式中，本申请涉及的锂离子电池通过将上述正负极极片叠片制成。
在一些实施方式中，本申请涉及的锂离子电池可包括外包装，所述外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，如聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)等中的一种或几种。
在一些实施方式中，本申请还提供了一种电池模块。该电池模块包括上述锂离子电池。电池模块采用了上述锂离子电池，因此至少具有与所述锂离子电池相同的优势。电池模块所含锂离子电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
在一些实施方式中，本申请还提供了一种电池包、其包括上述电池模块。所述电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
本申请第二方面提供了一种电化学装置，其包括本申请第一方面所述的锂离子电池。一些实施方式中，所述电化学装置包括，但不限于：电动车辆、混合动力电动车辆、插电式混合动力电动车辆、蓄电系统等。为了满足该电化学装置对锂离子电池的高功率和高能量密度的需求，可以采用电池包或电池模块。在另一些实施方式中，电化学装置可以是手 机、平板电脑、笔记本电脑等。该电化学装置通常要求轻薄化，可以采用锂离子电池作为电源。
下面结合实施例，进一步阐述本申请。应理解，这些实施例仅用于说明本申请而不用于限制本申请的范围。
锂离子电池的制备
(1)正极的制备：
将正极活性材料LiFePO4、导电剂Super P以及粘合剂聚偏二氟乙烯(PVDF)按照约96：2：2的重量比混合在溶剂N-甲基吡咯烷酮(NMP)中，搅拌均匀得到浆料。将此浆料涂覆于正极集流体铝箔上，烘干、冷压得到正极活性物质层，然后再经过裁片、分切、以及焊接极耳，得到正极。
(2)负极的制备：
实施例1至实施例44和对比例1至对比例5：
将具有不同OI值的天然石墨、导电剂Super P、增稠剂羧甲基纤维素钠按照重量比95:2:3在适量的去离子水溶剂中充分搅拌混合，使其形成均匀的负极浆料。将此浆料涂覆在负极集流体铜箔上，烘干、冷压得到负极活性物质层，然后再经过裁片、分切、以及焊接极耳，得到负极。
(3)电解液制备：
实施例1-30和对比例1-3：在含水量<10ppm的氩气气氛手套箱中，将一定量的有机溶剂碳酸亚乙酯(EC)和碳酸二乙酯(DEC)混合均匀，将充分干燥的锂盐LiPF6溶解于上述有机溶剂，获得电解液。其中，锂盐LiPF6重量百分含量为12.5％，碳酸乙烯酯(EC)的重量百分含量为26％，其余为DEC(电解液中各物质的含量均是基于电解液的重量计算得到)。向电解液中加入表1所示含量的碳酸亚乙烯酯和氟代碳酸乙烯酯。
实施例31-44和对比例4-3：在含水量<10ppm的氩气气氛手套箱中，将一定量的有机溶剂碳酸亚乙酯(EC)及碳酸二乙酯(DEC)混合均匀，将充分干燥的锂盐LiPF6溶解于上述非水溶剂，获得电解液，其中，锂盐LiPF6重量百分含量为12.5％，EC的重量百分含量为26％，VC的重量百分含量为2.5％，FEC的重量百分含量为1％，其余为DEC。向电解液中以表2所示的含量的量加入化合物B。
(4)隔离膜的制备：
以聚乙烯(PE)多孔薄膜作为隔离膜，孔隙率为35％。
(5)锂离子电池的制备：
将正极、隔离膜、负极按顺序叠好，使隔离膜处于正极和负极之间起到隔离的作用，然后卷绕得到裸电芯；将裸电芯置于外包装箔铝塑膜中，将上述制备好的电解液注入到干燥后的裸电芯中，经过真空封装、静置、化成、整形、容量测试等工序，即完成锂离子电池的制备。
测试方法：
1、锂离子电池循环测试：
常温循环性能测试：将以上实施例及对比例的锂离子电池成品置于25℃恒温箱中，静置30分钟，使锂离子电池达到恒温。将达到恒温的锂离子电池以1C恒流充电至电压为3.6V，然后以3.6V恒压充电至电流小于等于0.05C，接着以1C恒流放电至电压为2.8V，此为一个充放电循环，同时测试电芯厚度。以首次放电的容量为100％，反复进行充放电循环1000次，停止测试，记录对应的放电容量，容量保持率的计算公式如下：
容量保持率＝(循环后放电容量/首次放电容量)×100％。
负极极片的循环膨胀率测试：将负极冷压后的厚度记为H0，将循环1000次后的电芯满充，拆解电池并测试对应负极极片的厚度，记为H1，负极极片厚度变化率的计算公式如下：
负极极片厚度变化率＝(H1/H0-1)×100％
2、锂离子二次电池高温存储测试：
满充存储：将以上实施例及对比例的锂离子电池成品置于25℃的恒温箱中搁置5分钟，以1C的倍率恒流充电至3.6V，再恒压充电至电流小于等于0.05C，之后搁置5分钟，以1C倍率，恒电流放电至2.8V，再以1C的倍率恒流充电至3.6V，恒压充电至电流小于等于0.05C，之后将满充状态的锂离子二次电池置入60℃的烘箱中存储90天，在存储90天后，将锂离子电池取出并观察及记录其厚度变化量，厚度增长率的计算公式如下：
厚度增长率＝(高温存储后厚度-高温存储前厚度)/高温存储前厚度×100％。
3、锂离子二次电池直流阻抗测试(DCR测试)：
将以上实施例及对比例的锂离子电池成品置于25℃的恒温箱中搁置5分钟，以1C的倍率恒流充电至3.6V，再恒压充电至电流小于等于0.05C，静置30分钟，以0.1C的电流放电10秒(0.1秒取点一次，记录对应电压值U1)，以1C的电流放电360秒(0.1秒取点一次，记录对应电压值U2)。重复充放电步骤5次。“1C”是在1小时内将电池容量完全放完的电流值。
按如下公式计算得出直流阻抗(DCR)：R＝(U1-U2)/(1C-0.1C)。所得出的DCR即为 本申请的浓差极化阻抗，其为50％SOC(即荷电状态，state of charge)状态下的值，即实施例中的50％SOC DCR，单位为毫欧姆。
4、负极材料的OI值测试：
OI值采用X射线衍射仪进行测试(例如Bruker D8Discover型X射线衍射仪)，可以参考JISK 0131-1996。具体方法：将所述负极极片直接置于X射线衍射仪中，通过X射线分析法得到负极极片中负极活性材料的004晶面衍射峰的峰面积C004以及110晶面衍射峰的峰面积C110，负极极片的OI值＝C004/C110。
5、负极材料的BET值测试：
所述负极的比表面积BET可以采用本领域已知的方法测试。例如可以参照GB/T19587-2017，采用氮气吸附比表面积分析测试方法测试，并用BET(Brunauer Emment Teller)法计算得出，其中氮气吸附比表面积分析测试可以通过美国Micromeritics公司的Tri-Star 3020型比表面积孔径分析测试仪测试。首先拆解实施例及对比例中所述的电池，把拆出来的负极片浸泡在分散剂中，以便负极材料分散到分散剂中(乙醇)，然后超声30分钟后，将得到的材料放入真空干燥箱中干燥，最后使用比表面积测试仪对负极材料比表面积进行测量。
6、负极材料的Dv50值测试：
在本申请中，所述负极活性材料的Dv50值可参照标准GB/T 19077.1-2016，使用激光粒度分析仪(如Malvern Master Size 300)测定。其中，Dv50表示所述负极活性材料的累计体积分布百分数达到50％时所对应的粒径。
根据上述测试方法测试所制备的锂离子电池，测试结果如表1和表2所示
[表1]

通过表1中实施例1-30与对比例1-3对比，当负极材料的OI值较小时，
负极极片的压实密度在合适范围，天然石墨在嵌锂过程中的方向选择性较小，嵌锂膨胀可被分散到各个方向，降低极片和电池的循环膨胀，由于碳酸亚乙烯酯及氟代碳酸乙烯 酯形成的SEI膜阻抗较大，因此在保证性能的前提下应适量的添加添加剂；而当负极材料的OI值较大时，极片和电池的循环膨胀较严重，且材料端面变多导致表面副反应会增多，产气恶化，这时需要更多的碳酸亚乙烯酯及氟代碳酸乙烯酯对负极材料进行保护，改善膨胀及产气问题，所以当0.3≤a/(b+c)≤6时，锂离子电池具有较优的循环性能和低的阻抗；另外，碳酸亚乙烯酯主要生成PEO型聚合物SEI膜，氟代碳酸乙烯酯主要生成LiF等含无机成分SEI膜，两者含量要满足0.01≤b+c≤10、0.5≤b/c≤2.5时才能在负极表面形成富含有机和无机成分的SEI膜，该膜具有一定的韧性和弹性，能够减少因为天然石墨体积膨胀带来的SEI膜破坏进而引起的循环和存储性能恶化等一系列问题；且适当的电解液保有量可以提高电池的循环性能。
[表2]
表2中实施例31-44和实施例27和对比例4、对比例5相比，当负极材料的BET过大时，材料表面副反应会增多导致DCR及产气恶化，另外BET较大带来的材料水分含量 升高会进一步导致HF升高；当负极材料的BET过小时，锂离子传输速度较慢，影响循环性能。在电解液中添加式(II)所表示的含氮杂环化合物B，可以显著改善电池的高温存储性能，这主要是由于含氮杂环化合物在负极表面可以形成稳定的SEI膜，抑制循环和存储过程中溶剂和其他成膜添加剂的消耗；另外，式(II)所表示的含氮杂环化合物B中的含氮阳离子部分不仅能够促进锂盐解离，还能与路易斯碱如碳酸乙烯酯(EC)等络合，提高EC电解液氧化稳定性。但是含氮杂环化合物含量过高时存储不会进一步改善，这会导致形成的SEI膜过厚使阻抗增加，进而增加DCR值，因此可以适当添加式(II)所表示的含氮杂环化合物B，使其发挥最优的性能。
尽管已经演示和描述了说明性实施例，本领域技术人员应该理解上述实施例不能被解释为对本申请的限制，并且可以在不脱离本申请的精神、原理及范围的情况下对实施例进行改变，替代和修改。

Claims (10)

  1. 一种锂离子电池，其特征在于，所述锂离子电池包括电解液和负极极片，所述电解液包括电解液添加剂，所述电解液添加剂包括碳酸亚乙烯酯和氟代碳酸乙烯酯；所述负极极片包括负极活性材料，并且
    所述负极活性材料的OI值为a；基于所述电解液的重量，所述碳酸亚乙烯酯的重量百分含量为b％，所述氟代碳酸乙烯酯的重量百分含量为c％；所述a、b和c满足：
    0.3≤a/(b+c)≤6，
    0.02≤b+c≤10，
    0.1＜b/c＜3。
  2. 根据权利要求1所述的锂离子电池，其中，所述锂离子电池满足以下条件至少一者：
    (1)0.4≤a/(b+c)≤3；
    (2)0.2≤b+c≤5；
    (3)0.5≤b/c≤2.5。
  3. 根据权利要求1或2所述的锂离子电池，其中，所述锂离子电池满足以下条件至少一者：
    (ⅰ)所述a的范围为：2≤a≤15；
    (ⅱ)所述b的范围为：0.01≤b≤10；
    (ⅲ)所述c的范围为：0.01≤c≤10。
  4. 根据权利要求1至3中任一项所述的锂离子电池，其中，所述锂离子电池满足以下条件至少一者：
    (Ⅰ)所述a的范围为：3≤a≤7；
    (Ⅱ)所述b的范围为：0.1≤b≤5；
    (Ⅲ)所述c的范围为：0.1≤c≤5。
  5. 根据权利要求1至4中任一项所述的锂离子电池，其中，所述锂离子电池的保液系数为e，所述b、c和e满足：0.01≤e×(b+c)≤50。
  6. 根据权利要求1至5中任一项所述的锂离子电池，其中，所述锂离子电池的保液系数e的范围为：1≤e≤7。
  7. 根据权利要求1至6中任一项所述的锂离子电池，其中，所述负极活性材料的比表面积为f m2/g，所述f的范围为：1≤f≤3。
  8. 根据权利要求1至7中任一项所述的锂离子电池，其中，所述电解液包括式(II)所表示的化合物B：
    其中:
    R6、R7、R8、R9和R10各自独立地选自氢、氰基、卤素原子、C1-10烷基、C2-10烯基、C2-10炔基、C3-6杂环基、C5-6芳基、C5-6杂芳基、-R11-(C＝O)-R12-、-R11-(C＝O)-O-R12-、-R11-(C＝O)-NH-R12-、或者R6、R7、R8、R9和R10中任意相邻的两者相互连接以形成C1-10的环状结构；其中，R11和R12各自独立地选自单键、C1-10烷基、C2-10烯基、C2-10炔基、C3-6杂环基、C5-6芳基或C5-6杂芳基；所述C1-10烷基、C2-10烯基、C2-10炔基、C3-6杂环基、C5-6芳基、C5-6杂芳基或C1-10的环状结构任选地被一个或更多个氨基、氰基、卤素原子、C1-3烷基、C3-6杂环基、C5-6杂芳基所取代。
  9. 根据权利要求8所述的锂离子电池，其中，所述式(II)所表示的化合物B包括以下中的至少一者：吡啶、2-甲基吡啶、2-乙烯基吡啶、2-乙炔基吡啶、2-氟吡啶、2-氰基吡啶、3-乙烯基吡啶，3-氟吡啶、2,6-二氟吡啶、五氟吡啶、2,2'-联吡啶、三联吡啶、1,8-萘啶、5,6,7,8-四氢喹啉；
    基于所述电解液的重量，所述式(II)所表示的化合物的重量百分含量为k％，所述k的范围为：0≤k＜3。
  10. 一种电化学装置，其特征在于，所述电化学装置包括权利要求1至9中任一项所述的锂离子电池。
PCT/CN2023/091190 2022-09-30 2023-04-27 锂离子电池以及包含其的电化学装置 WO2024066339A1 (zh)

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CN115411346A (zh) * 2022-09-30 2022-11-29 宁德新能源科技有限公司 锂离子电池以及包含其的电化学装置

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