Lithium ion battery and electric device

Abstract

The invention provides a lithium ion battery and a power utilization device, and belongs to the technical field of battery materials, the lithium ion battery at least comprises a negative plate and an electrolyte, and the electrolyte comprises an organic solvent and an additive; the organic solvent comprises a carboxylic ester solvent, and the additive comprises methylene methanedisulfonate; in the lithium ion battery, the mass percentage content a of the carboxylic ester solvent in the electrolyte, the mass percentage content b of methylene methanedisulfonate in the electrolyte and the ester exchange rate c of the negative plate meet the following relation: (a * c) / b is more than or equal to 0.01 and less than or equal to 64. According to the lithium ion battery provided by the invention, by adjusting the addition amount of the carboxylic ester solvent and the additive methylene methanedisulfonate in the electrolyte and the ester exchange rate of the negative plate and comprehensively controlling the numerical relationship among the carboxylic ester solvent, the additive methylene methanedisulfonate and the negative plate, the fast charging capacity and the high-temperature cycle life of the lithium ion battery are improved at the same time.

Description

Technical Field

[0001] This invention belongs to the field of battery material technology, specifically relating to a lithium-ion battery and an electrical device. Background Technology

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and light weight, have become the primary power source widely used in portable electronic devices, electric vehicles, and energy storage systems. With the continuous expansion of application scenarios, especially in the electric vehicle sector, improving battery fast-charging capability has become one of the key performance indicators.

[0003] However, the high-rate current during fast charging causes lithium ions to embed into the graphite anode far exceeding its kinetic limit. Excess lithium ions are reduced to metallic lithium on the anode surface, forming dendrites. Lithium dendrites can pierce the separator, causing internal short circuits. "Dead lithium" detached from the electrode will permanently lose active lithium. Every 1% increase in lithium deposition can lead to approximately 7% capacity decay. Moreover, when the temperature exceeds 45°C, the electrolyte decomposition rate accelerates, and the rupture and regeneration of the SEI film (solid electrolyte interface) on the anode surface are accelerated, continuously consuming active lithium ions and leading to a decrease in battery cycle life. Therefore, a core challenge in the current development of lithium-ion battery technology is how to simultaneously improve the battery's fast-charging performance and long-term cycle stability at high temperatures.

[0004] Based on this, the present invention provides a lithium-ion battery that balances improved fast charging performance and cycle life. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a lithium-ion battery that improves both the fast charging performance and cycle life of the battery.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a lithium-ion battery, the lithium-ion battery comprising at least a negative electrode and an electrolyte, the electrolyte comprising an organic solvent and additives;

[0008] The organic solvent includes carboxylic acid ester solvents, and the additive includes methylene methane disulfonate;

[0009] In the lithium-ion battery, the carboxylic acid ester solvent, methylene methane disulfonate, and the negative electrode sheet satisfy the following relationship: 0.01≤(a×c) / b≤64;

[0010] Where a is the mass percentage of carboxylic acid ester solvent in the electrolyte, b is the mass percentage of methylene disulfonate in the electrolyte, and c is the transesterification rate of the negative electrode.

[0011] In this invention, the range of (a×c) / b is 0.01-64, for example, it can be 0.01, 0.03, 0.05, 0.1, 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60 or 64, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0012] The lithium-ion battery provided by this invention adds a carboxylic acid ester solvent to the electrolyte to enhance the battery's fast-charging capability. The carboxylic acid ester solvent, together with the additive methylene disulfonate and the ester exchange rate of the negative electrode, synergistically controls the battery's fast-charging performance while also improving its high-temperature cycle life.

[0013] In a second aspect, the present invention provides an electrical device comprising the lithium-ion battery described in the first aspect.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] The lithium-ion battery provided by this invention synergistically regulates the addition amounts of carboxylic acid ester solvent and the additive methylene methane disulfonate in the electrolyte, as well as the transesterification rate of the negative electrode. Increasing the content of carboxylic acid ester solvent in the electrolyte can reduce the overall viscosity of the electrolyte and increase the self-diffusion coefficient of lithium ions, thereby improving the battery's fast-charging performance. However, if the carboxylic acid ester solvent is added in excess, a reduction reaction will occur on the negative electrode surface, generating unstable byproducts. These byproducts cannot form a dense and stable solid electrolyte interphase (SEI) film. Defects in the SEI film will lead to continuous decomposition of the electrolyte, consuming active lithium and thus shortening the cycle life. By adding the additive methylene methane disulfonate, a stable SEI film can be formed on the negative electrode. At the same time, the transesterification rate of the negative electrode can be controlled to reduce side reactions between the negative electrode and the electrolyte, reduce the consumption of active lithium, and thus improve the battery's cycle life. By comprehensively controlling the numerical relationship between the three factors, both the fast-charging capability and high-temperature cycle life of the lithium-ion battery are balanced. Detailed Implementation

[0016] This invention provides a lithium-ion battery, which includes at least a negative electrode and an electrolyte. The electrolyte includes an organic solvent and an additive. The organic solvent includes a carboxylic acid ester solvent, and the additive includes methylene methane disulfonate. In the lithium-ion battery, the carboxylic acid ester solvent, methylene methane disulfonate, and the negative electrode satisfy the following relationship: 0.01 ≤ (a × c) / b ≤ 64; where a is the mass percentage of the carboxylic acid ester solvent in the electrolyte, b is the mass percentage of methylene methane disulfonate in the electrolyte, and c is the transesterification rate of the negative electrode.

[0017] In this invention, the transesterification rate of the negative electrode is used to quantify its ability to catalyze transesterification reactions and can reflect the electron passivation capability of the negative electrode.

[0018] The transesterification reaction refers to the process by which an ester compound reacts with an alcohol compound or another ester compound to generate a new ester compound.

[0019] The transesterification rate of the negative electrode refers to the percentage of the total mass of all reactants before the reaction generated when an ester compound undergoes a transesterification reaction with an alcohol compound or another ester compound under the action of the negative electrode.

[0020] That is, the transesterification rate of the negative electrode = (mass of the generated ester compounds / total mass of reactants) × 100%.

[0021] The specific test method for the ester exchange rate of the negative electrode is as follows:

[0022] (1) Mix the ester compound with an alcohol or another ester compound to prepare a reactant solution. Place the negative electrode in the reactant solution. The amount of reactant solution is calculated as: electrode capacity × 12 mL. The unit of electrode capacity is Ah. Then seal the container.

[0023] (2) The sealed negative electrode was placed under the test temperature to carry out the transesterification reaction. After the reaction was completed, the components of the product were analyzed and the mass of the generated ester compounds was determined.

[0024] (3) The transesterification rate of the negative electrode was calculated.

[0025] For example, under a test temperature of 60°C, the ester compounds in the reactants are selected from methyl ethyl carbonate, the alcohol compounds are selected from propylene glycol, the mass ratio of methyl ethyl carbonate to propylene glycol is 1:1, and the generated ester compounds are dimethyl carbonate and diethyl carbonate; the component analysis of the product is performed by gas chromatography; the transesterification rate of the negative electrode is calculated as: (mass of dimethyl carbonate / total mass of methyl ethyl carbonate and propylene glycol) × 100%.

[0026] Preferably, the carboxylic acid ester solvent, methylene methane disulfonate, and negative electrode sheet satisfy the following condition: 0.5 ≤ (a×c) / b ≤ 9. The numerical range of (a×c) / b can be 0.5, 1, 2, 3, 4, 5, 6, 7, 8, or 9, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable.

[0027] Preferably, the electrolyte contains 5%-70% by mass of carboxylic acid ester solvent, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, and more preferably 20%-60%.

[0028] Controlling the content of carboxylic acid esters can, on the one hand, reduce the viscosity of the electrolyte, improve the diffusion ability of lithium ions in the electrolyte, and enhance the fast charging performance of the battery; on the other hand, it can reduce the side reactions between the electrolyte and the negative electrode, and improve the high-temperature cycle life of the battery.

[0029] Preferably, the mass percentage of methylene methane disulfonate in the electrolyte is 0.1%-1.5%, for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, and it is more preferably 0.3%-1%.

[0030] Controlling the content of methylene disulfonate can, on the one hand, preferentially reduce it on the negative electrode surface to generate a stable Li2SO3 / Li2SO4 inorganic interface layer, thereby reducing the loss of active lithium during high-temperature cycling and improving the high-temperature cycle life of the battery; on the other hand, it can avoid the formation of an excessively thick SEI film, which increases interfacial impedance, hinders the migration of lithium ions, and improves the fast-charging performance of the battery.

[0031] Preferably, the ester exchange rate of the negative electrode is 0.1%-10%, for example, it can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. More preferably, it is 1%-5%.

[0032] Controlling the ester exchange rate of the negative electrode sheet ensures rapid lithium ion insertion and extraction at the negative electrode, improving the battery's insertion and extraction performance. On the other hand, it reduces side reactions at the electrolyte-negative electrode interface, improving the battery's high-temperature cycle life.

[0033] The lithium-ion battery is formed by encapsulating the electrolyte and electrode sheets. The transesterification rate of the negative electrode sheet can be controlled by the formation current and settling time during the formation process. By controlling the formation current and settling time, a stable SEI film can be formed on the surface of the negative electrode sheet, reducing side reactions with the electrolyte.

[0034] Preferably, the formation includes at least one charging and resting process.

[0035] Preferably, the initial formation current is 0.01-0.1C, for example, it can be 0.01C, 0.03C, 0.05C, 0.08C or 0.1C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the initial settling time for the formation is 10-30 minutes, for example, it can be 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the carboxylic acid ester solvent includes C2-C8 carboxylic acid ester compounds.

[0038] The C2-C8 refers to compounds with 2 to 8 carbon atoms, for example, 2, 3, 4, 5, 6, 7 or 8.

[0039] Preferably, the carboxylic acid ester solvent includes any one or a combination of at least two of ethyl acetate, ethyl propionate, methyl propionate, or methyl acetate. Typical but non-limiting combinations include combinations of ethyl acetate and ethyl propionate, combinations of ethyl propionate and methyl propionate, combinations of methyl propionate and methyl acetate, combinations of ethyl acetate, ethyl propionate, and methyl propionate, combinations of ethyl propionate, methyl propionate, and methyl acetate, or combinations of ethyl acetate, ethyl propionate, methyl propionate, and methyl acetate.

[0040] Preferably, the organic solvent further includes carbonate solvents.

[0041] Preferably, the carbonate solvent includes any one or a combination of at least two of ethylene carbonate, ethyl methyl carbonate, or dimethyl carbonate. Typical but non-limiting combinations include combinations of ethylene carbonate and ethyl methyl carbonate, combinations of ethyl methyl carbonate and dimethyl carbonate, combinations of ethylene carbonate and dimethyl carbonate, or combinations of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0042] Preferably, the electrolyte contains 30%-80% by mass of carbonate solvent, for example, 30%, 40%, 50%, 60%, 70% or 80%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, the additive further includes at least one of vinylene carbonate, fluoroethylene carbonate, or vinyl sulfite.

[0044] Adding vinylene carbonate (VC) to the electrolyte allows it to preferentially decompose on the negative electrode surface to form a Li₂CO₃-based organic layer. Adding fluoroethylene carbonate (FEC) induces the formation of a LiF-containing inorganic layer from the fluorine atoms, resulting in a dense and stable SEI film. The combination of vinylene carbonate and fluoroethylene carbonate enhances the mechanical strength and ionic conductivity of the SEI film. Vinyl sulfite helps reduce SEI film impedance; its sulfonic acid groups promote lithium-ion migration while inhibiting electrolyte decomposition at high temperatures.

[0045] Preferably, the negative electrode sheet includes a current collector and a negative electrode material layer coated on at least one side of the current collector.

[0046] Preferably, the compaction density of the negative electrode material layer is 1.2-1.8 g / cm³. 3 For example, it could be 1.2 g / cm³. 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 Or 1.8g / cm 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0047] Controlling the compaction density of the negative electrode material layer within a certain range ensures uniform coating of the negative electrode material layer, promotes rapid lithium-ion transport, and improves the fast-charging performance of the battery. On the other hand, it avoids excessive gaps between negative electrode active material particles, reduces side reactions at the electrolyte-negative electrode interface, and improves the high-temperature cycle life of the battery.

[0048] In this invention, the compaction density of the negative electrode material layer is tested using the following method:

[0049] The battery was discharged at 0.33C and disassembled to obtain the negative electrode sheet. The negative electrode sheet was soaked in dimethyl carbonate (DMC) solution for 4 hours and then dried. The pretreated negative electrode sheet was cut into circular pieces of fixed area using a punching machine. The area of ​​the circular piece was recorded as S0. Three circular pieces were taken as parallel samples, and the mass of the three circular pieces was weighed using an electronic balance. The average value was recorded as M1. The thickness of the negative electrode material layer in the three circular pieces was measured using a micrometer. The thickness of the negative electrode material layer is the total thickness of the negative electrode sheet minus the thickness of the current collector. The average value was recorded as H. Finally, an appropriate amount of deionized water was dropped onto each of the three circular pieces. The coating on the circular pieces was gently wiped off with lint-free paper to expose the copper foil. The pieces were left to stand at room temperature (or dried) for 10 minutes. After the copper foil was dried, the mass of the three copper foil pieces was weighed and the average value was recorded as M0. The compaction density A of the negative electrode sheet was calculated according to the following formula: A=(M1-M0) / (H×S0).

[0050] Preferably, the ionic conductivity of the negative electrode material layer is 0.1-1 mS / cm, for example, it can be 0.1 mS / cm, 0.2 mS / cm, 0.3 mS / cm, 0.4 mS / cm, 0.5 mS / cm, 0.6 mS / cm, 0.7 mS / cm, 0.8 mS / cm, 0.9 mS / cm or 1 mS / cm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] By controlling the ionic conductivity of the negative electrode material layer, lithium ions can be efficiently inserted and extracted. On the one hand, this enables rapid insertion and extraction of lithium ions on the electrode surface, improving lithium ion transport efficiency and ensuring the fast-charging performance of the battery. On the other hand, it enables uniform insertion of lithium ions, suppressing lithium dendrites and ensuring the cycle life of the battery.

[0052] In this invention, the ionic conductivity of the negative electrode material layer is tested using the following method:

[0053] The battery was discharged at 0.33C, and the negative electrode was obtained after disassembly. The negative electrode was taken, its thickness was measured, and it was cut into pieces the size of the positive electrode (60×75mm) and the solid electrode (60×45mm). The pieces were then dried, stacked, assembled, and injected with 2mL of electrolyte. The battery was held in place by a 0.07MPa glass clamp and subjected to EIS testing at a frequency of 0.1-10. 6 With a Hz, 5mV disturbance voltage, a transmission line model (TLM) was established using Nyquist curves from EIS data of a symmetrical battery. Equivalent circuit fitting was then performed to obtain the ionic resistance R. ion The ionic conductivity was calculated using the following formula: Ionic conductivity = Electrode thickness / (Ionic resistance R) ion ×Electrode contact area).

[0054] Preferably, the porosity of the negative electrode material layer is 30%-50%, for example, it can be 30%, 35%, 40%, 45% or 50%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] Controlling the porosity of the negative electrode material layer can shorten the lithium ion transport path and improve the battery's fast charging performance, while also reducing side reactions at the electrolyte-negative electrode interface and improving the battery's high-temperature cycle life.

[0056] In this invention, the porosity of the negative electrode material layer is tested using the following method:

[0057] The battery was discharged at 0.33C, and the negative electrode sheet was obtained after disassembly. Using an electrode sheet punching machine, the negative electrode sheet was cut into round pieces with a diameter of 19mm. Simultaneously, the thickness of the negative electrode sheet and the current collector were measured using a micrometer. The mass was measured using a balance with an accuracy of 0.0001g, and the volume of the cut negative electrode sheet was calculated. The negative electrode sheet was then immersed in a sealed container containing hexadecane for 1 hour. The negative electrode sheet was removed with tweezers and placed on lint-free paper to absorb dryness until a constant weight was reached (generally, 1 hour is sufficient). The mass was then measured again. The porosity was calculated using the formula: Porosity = (Mass after immersion - Mass before immersion) / (Density × Volume), where the density was 0.7734 g / cm³. 3 .

[0058] Preferably, the negative electrode material layer comprises a negative electrode active material.

[0059] Preferably, the negative electrode active material includes graphite and / or silicon-based materials.

[0060] Preferably, the silicon-based material comprises silicon-carbon and / or silicon-oxygen.

[0061] Preferably, the particle size range of the silicon-based material is 50-300nm, for example, it can be 50nm, 100nm, 150nm, 200nm, 250nm or 300nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0062] Preferably, the graphite comprises primary particulate graphite and / or secondary particulate graphite.

[0063] Preferably, the mass content of secondary particle graphite in the graphite is 50%-100%, for example, it can be 50%, 60%, 70%, 80%, 90% or 100%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0064] Preferably, the primary graphite particles have a particle size of 1-15 μm, and the secondary graphite particles have a particle size of 6-20 μm. The particle size of the primary graphite particles can be 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, or 15 μm, and the particle size of the secondary graphite particles can be 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, or 20 μm, but is not limited to the listed values; other unlisted values ​​within the range are also applicable.

[0065] Controlling the particle size of the negative electrode active material ensures smooth lithium-ion transport and improves the battery's fast-charging performance. On the other hand, it reduces side reactions between the electrolyte and the negative electrode active material, thereby improving the battery's high-temperature cycle life.

[0066] In the present invention, the lithium-ion battery is prepared by the following preparation method:

[0067] (1) Preparation of the positive electrode sheet: The positive electrode active material, conductive agent, binder, and dispersant are mixed uniformly according to a mass ratio of (90-99):(0.5-5):(0.5-5):(0-2), and a solvent is added to obtain a positive electrode slurry. The positive electrode slurry is coated on at least one surface of the positive electrode current collector, and after drying, rolling, and cutting, a positive electrode sheet is obtained.

[0068] In the above positive electrode sheet, the positive electrode active material is selected from at least one of lithium cobalt oxide, nickel cobalt ternary material, lithium manganese oxide, lithium iron phosphate, lithium nickel manganese oxide, or lithium manganese iron phosphate.

[0069] Specifically, the chemical general formula of the nickel cobalt ternary material can be expressed as: Li a Ni b Co c M1 d M2 e O f R g , where 0.75 ≤ a ≤ 1.2, 0 < b < 1, 0 < c < 1, 0 < d < 1, b + c + d = 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3; M1 can be Mn and / or Al, M2 is selected from at least one of B, Zr, Ti, Si, Mo, La, Ce, Te, Nb, Ta, Si, Al, W, Sr, V, Y, Mg, Co, or Li, and the content of M2 in the nickel cobalt ternary material is 100-10000 ppm; R includes but is not limited to at least one of N, F, S, or Cl.

[0070] Specifically, lithium nickel manganese oxide is a positive electrode active material with a spinel structure and has the advantage of high voltage characteristics. Its chemical general formula can be expressed as: Li 1+x Ni y M z Mn 2-x-y-z O 4-k , where -0.1 ≤ x ≤ 0.2, 0.4 ≤ y ≤ 0.6, 0 ≤ z ≤ 0.2, 0 ≤ k ≤ 0.1, M is a doping element, and M includes but is not limited to at least one of Cr, Mo, Nb, Ru, P, S, Ta, W, or Ti.

[0071] Specifically, lithium manganese iron phosphate is a positive electrode active material with an olivine structure and a hexagonal close-packed structure at the same time. Its chemical general formula can be expressed as: Li a G b Fe x Mn y M 1-x-y P 1-m Q m O4-n R n Wherein, 0.9≤a≤1.1, 0≤b≤0.1, 0.001≤x≤0.999, 0.001≤y≤0.999, 0≤1-xy≤0.1, 0≤m≤0.1, 0≤n≤0.1; M represents a doping element at the manganese and / or iron sites, M including but not limited to at least one of Co, Mg, Zn, Ca, Ti, V, Ni or Cr; G represents a doping element at the lithium sites, G including but not limited to at least one of Zn, Al, Na, K, Mg, Nb, Mo or W; Q represents a doping element at the phosphorus sites, Q including but not limited to at least one of B, S, Si or N; R represents a doping element at the oxygen sites, R including but not limited to at least one of S, F, Cl or Br.

[0072] Specifically, lithium iron phosphate is a positive electrode active material with an olivine-type crystal structure, possessing advantages such as low cost and high safety. Its general chemical formula can be represented as: LiFe 1-x M x PO y Q z Where x≤0.1, 3.85≤y≤4, 0≤z≤0.05; M is a doping element, including but not limited to at least one of Mn, Ni, Co, Cr, Cu, Bi or Sb, and the content of M in lithium iron phosphate is 500-5000ppm.

[0073] In the above positive electrode, the conductive agent is selected from at least one of superconducting carbon (SP), acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0074] In the above-mentioned positive electrode sheet, the binder is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin.

[0075] In the aforementioned positive electrode sheet, the dispersant is selected from at least one of acrylic acid, acrylate, polyether ester, phosphate ester, small molecule alkanolamine, polyurethane, modified styrene / maleic anhydride, hydrogenated nitrile butadiene rubber (HNBR), polyvinylpyrrolidone (PVP), or polyethylene glycol (PEG). When the positive electrode active material is selected from lithium iron phosphate and / or lithium manganese iron phosphate, a dispersant is used.

[0076] In the above-mentioned positive electrode, the positive current collector can be a metal foil or a composite current collector.

[0077] Specifically, the metal foil can be aluminum or an aluminum alloy.

[0078] Specifically, the composite current collector includes an intermediate high-molecular layer and metal layers disposed on both sides of the polymer layer; wherein, the polymer layer includes polymer materials, including at least one of polyamide (PA), polyterephthalate, polyimide (PI), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), aramid, acrylonitrile-butadiene-styrene copolymer (ABS), polybutylene terephthalate (PET), poly(p-phenylene terephthalamide) (PPTA), polypropylene (PPE), polyoxymethylene (POM), epoxy resin, phenolic resin, polytetrafluoroethylene (PTEE), polyvinylidene fluoride (PVDF), silicone rubber, polycarbonate (PC), polyvinyl alcohol (PVA), polyethylene glycol (PEG), cellulose, starch, protein, its derivatives, its crosslinks or copolymers; the metal layer includes at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver or silver alloy.

[0079] (2) Preparation of negative electrode sheet: The negative electrode active material, conductive agent and binder are mixed in a mass ratio of (95-98):(0.2-1.5):(1-3), and a solvent is added to obtain a negative electrode slurry. The negative electrode slurry is coated on at least one surface of the negative electrode current collector, and the negative electrode sheet is obtained after drying, rolling and cutting.

[0080] In the aforementioned negative electrode sheet, the negative electrode active material is selected from carbon materials, silicon-based materials, or lithium titanate (Li4Ti5O). 12 At least one of the following.

[0081] Specifically, the carbon material is selected from at least one of natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, or soft carbon.

[0082] Specifically, the silicon-based material is selected from at least one of elemental silicon, silicon oxide, silicon carbide, or silicon alloy.

[0083] In the aforementioned negative electrode sheet, the conductive agent is selected from at least one of superconducting carbon (SP), conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0084] In the aforementioned negative electrode sheet, the binder is selected from at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resin, polyvinyl alcohol (PVA), sodium alginate (SA), or sodium carboxymethyl methacrylate (CMC). The waterborne acrylic resin may be at least one of polyacrylic acid (PAA), polymethacrylic acid (PMAA), sodium polyacrylate (PAAS), or polyacrylamide (PAM).

[0085] In the aforementioned negative electrode sheet, the negative electrode current collector is selected from metal foil or composite current collector.

[0086] Specifically, the metal foil can be copper or a copper alloy.

[0087] Specifically, the composite current collector includes an intermediate high-molecular layer and metal layers disposed on both sides of the polymer layer; wherein, the polymer layer includes polymer materials, including at least one of polyamide (PA), polyterephthalate, polyimide (PI), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), aramid, acrylonitrile-butadiene-styrene copolymer (ABS), polybutylene terephthalate (PET), poly(p-phenylene terephthalamide) (PPTA), polypropylene (PPE), polyoxymethylene (POM), epoxy resin, phenolic resin, polytetrafluoroethylene (PTEE), polyvinylidene fluoride (PVDF), silicone rubber, polycarbonate (PC), polyvinyl alcohol (PVA), polyethylene glycol (PEG), cellulose, starch, protein, its derivatives, its crosslinks or copolymers; the metal layer includes at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver or silver alloy.

[0088] (3) Electrolyte preparation: Mix carbonate solvent and carboxylic acid ester solvent to obtain organic solvent, then dissolve the dried lithium salt in the mixed organic solvent, add additives to obtain electrolyte.

[0089] In the electrolyte described above, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), or lithium tetrafluorooxalate phosphate (LiTFOP).

[0090] (4) Separator: The separator is placed between the positive electrode and the negative electrode to separate the positive electrode and the negative electrode and prevent the positive electrode and the negative electrode from short-circuiting.

[0091] The material of the diaphragm is selected from at least one of glass fiber, nonwoven fabric, polyethylene (PE), polypropylene (PP) and / or polyvinylidene fluoride.

[0092] Specifically, a coating may also be provided on the surface of the diaphragm. The coating may be an inorganic coating and / or an organic coating. The inorganic coating material includes at least one of alumina, silicon oxide, titanium oxide, magnesium oxide, zirconium oxide or boehmite. The organic coating includes at least one of aramid coating or polyvinylidene fluoride (PVDF) coating.

[0093] (5) Stack the positive electrode, separator and negative electrode in sequence so that the separator is between the positive and negative electrode sheets to play a role in isolation. Then wind them to obtain the bare cell. Place the bare cell in the outer packaging shell, dry it and inject electrolyte. After vacuum sealing, standing, formation and shaping, obtain the lithium-ion battery.

[0094] Steps (1) to (4) are not in any particular order.

[0095] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0096] Example 1

[0097] (1) Preparation of positive electrode sheet: According to the mass percentage of the positive electrode material layer composition, 97.42% lithium iron phosphate, 1.84% PVDF, 0.02% conductive agent (SP and SWCNT are formed in a mass ratio of 36:1) and 0.72% dispersant are mixed evenly and dispersed in N-methylpyrrolidone to obtain positive electrode slurry. The positive electrode slurry is coated on aluminum foil to obtain double-sided coated positive electrode sheet. Then the double-sided coated positive electrode sheet is rolled and cut to obtain positive electrode sheet.

[0098] (2) Preparation of negative electrode sheet: According to the mass percentage of the negative electrode material layer composition, 96.85% graphite, 0.6% conductive agent SP, 0.5% binder CMC, 1% binder SBR and 1.05% binder PAA are mixed evenly and dispersed in deionized water to obtain negative electrode slurry. The Dv50 particle size of graphite is 19.6μm. The negative electrode slurry is coated on copper foil to obtain double-sided coated electrode sheet, and then rolled and cut to obtain negative electrode sheet.

[0099] (3) Electrolyte preparation: Ethyl carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and ethyl acetate (EA) are mixed in a mass ratio of 3:2:3:2. Then, fully dried lithium salt lithium hexafluorophosphate (LiPF6) is dissolved in the mixed organic solvent to prepare an electrolyte with a lithium salt concentration of 1.1 mol / L. The electrolyte is allowed to stand in a refrigerator for 0.5 h. Methylene methane disulfonate (MMDS) is added as an additive at a mass percentage of 0.5 wt% of the electrolyte.

[0100] (4) Stack the positive electrode, separator and negative electrode in sequence, so that the separator is between the positive electrode and the negative electrode to play a role in isolation. Then wind to obtain the bare cell. Place the bare cell in the outer packaging shell, dry it and inject electrolyte. Vacuum seal it. Then let the battery stand for 24 hours, charge it at 0.05C current for 2 hours at 45°C, stand for 10 minutes, charge it at 0.33C current for 2 hours, stand for 10 minutes, complete the formation process, and finally obtain the lithium-ion battery after shaping.

[0101] The obtained lithium-ion battery was tested, including the ester exchange rate of the negative electrode, the mass percentage of carboxylic acid ester solvent in the electrolyte, and the mass percentage of methylene disulfonate additive. The results are shown in Table 1.

[0102] Example 2

[0103] The difference between this embodiment and Example 1 lies in the following: In the preparation step of the negative electrode sheet, the particle size of graphite, the initial formation current and the initial settling time of the formation process are changed to obtain different negative electrode sheets. In the electrolyte preparation step, the content of carboxylic acid ester solvent and the content of methanedisulfonate are changed, and additives such as vinylene carbonate, fluoroethylene carbonate and vinyl sulfite are added. Among them, vinylene carbonate, fluoroethylene carbonate, methanedisulfonate and vinyl sulfite are added according to the mass percentage of electrolyte of 1.5wt%, 1.0wt%, 0.5wt% and 0.3wt%, respectively. The rest of the preparation process is the same as in Example 1.

[0104] Example 3-19

[0105] The difference between Examples 3-19 and Example 1 is that in the preparation steps of the negative electrode sheet, the particle size of graphite, the initial formation current and the initial settling time of the formation process are changed to obtain different negative electrode sheets. In addition, in the electrolyte preparation steps, the type and content of carboxylic acid ester solvent and the content of the additive methane disulfonate are changed. The rest of the preparation process remains the same as in Example 1.

[0106] Comparative Examples 1-4

[0107] The difference between Comparative Examples 1-4 and Example 1 is that in the preparation steps of the negative electrode, the particle size of graphite, the initial formation current and the initial settling time of the formation process are changed to obtain different negative electrode sheets. In addition, in the electrolyte preparation steps, the content of carboxylic acid ester solvent and the content of the additive methane disulfonate are changed. The rest of the preparation process remains the same as in Example 1.

[0108] The variations in Dv50 particle size, initial formation current, initial settling time, and type of carboxylic acid ester solvent of graphite in the examples and comparative examples are shown in Table 1. The lithium-ion batteries obtained in the examples and comparative examples were tested, and the transesterification rate of the negative electrode, the mass percentage of carboxylic acid ester solvent in the electrolyte, and the mass percentage of the additive methane disulfonate (MMDS) were tested. The results are shown in Table 1.

[0109] The testing method is as follows:

[0110] (1) Ester exchange rate of the negative electrode:

[0111] The battery was discharged at 0.33C, and the negative electrode was obtained after disassembly. A 12×12cm aluminum-plastic film bag was made, and the edges of the bag were tightly sealed. A mixed solution of PA (propylene glycol) and EMC (ethyl methyl carbonate) in a 1:1 mass ratio was prepared and thoroughly mixed. The negative electrode of the battery was cut into 81mm×81mm pieces. The electrode was cleaned with a sufficient amount of DMC (dimethyl carbonate) solution, dried, and placed in the aluminum-plastic film bag. Using a dropper and a 15mL sample tube, 12mL of the electrode was added to the aluminum-plastic film bag. For each volume (unit / Ah) of PA-EMC mixed solution, at least three parallel samples are required to ensure data accuracy. After all storage bags are filled, the aluminum-plastic film bags are sealed with a handheld sealing machine. After sealing, it is necessary to check whether the seal is qualified and ensure that there is no leakage. The storage bags are stored at 60°C. Samples of different numbered storage bags need to be placed horizontally in a 60°C oven for 48 hours. After the resting period, the liquid in the storage bags is drawn off with a syringe and filtered. The amount of DMC generated is calculated using GC testing to calculate the transesterification rate.

[0112] (2) Content of carboxylic acid ester solvents and methylene methane disulfonate:

[0113] ① Electrolyte Collection: The secondary battery under test is discharged using a battery charging / discharging device under the following conditions: current 0.3C, cutoff voltage. After recording the battery number / barcode, the battery is disassembled and the electrolyte collected in a glove box (H2O≤0.1ppm, O2≤0.1ppm). There are three methods for collecting the electrolyte: After removing the battery cover, if there is free electrolyte, collect it into a 5mL sample tube using a pipette and seal it with sealing tape to prevent leakage; if there is no free electrolyte, it can be... Pressurize continuously using a hydraulic press (Beijing Heng'ao Technology Co., Ltd.'s FY-30 hydraulic press) until free electrolyte appears. Collect the electrolyte into a sample tube and seal it. Add an appropriate amount of dichloromethane extractant to the battery and record the dichloromethane content. After adding dichloromethane, put the battery into an aluminum-plastic bag and seal it with a heat sealer. Transfer it to an ultrasonic oscillator and oscillate for 12 hours to allow the electrolyte in the electrode to mix thoroughly with the dichloromethane. Then, use a pipette to draw the mixture of dichloromethane and electrolyte into a 5mL sample tube and seal the sample tube with sealing tape.

[0114] ② The collected electrolyte sample was injected into an Agilent Intuvo 9000 gas chromatograph-mass spectrometer using a microsyringe for testing to obtain GC-MS chromatograms. Carboxylic acid ester solvents or methylene disulfonate were dissolved in EMC solvent to prepare solutions of different concentrations, which were then injected into the Agilent Intuvo 9000 gas chromatograph-mass spectrometer to obtain standard GC-MS chromatograms. The GC-MS chromatogram of the electrolyte to be tested was compared with the standard GC-MS chromatogram to confirm the presence of the corresponding components. The content of the corresponding components was then determined based on the peak area of ​​the corresponding components in the electrolyte to be tested.

[0115] Table 1

[0116]

[0117]

[0118] Performance testing

[0119] The relationship between the content of carboxylic acid ester solvent a, the content of methylene disulfonate (MMDS) b, and the transesterification rate c of the negative electrode in the lithium-ion battery was calculated using the formula (a×c) / b. The lithium-ion batteries obtained in the examples and comparative examples were tested for fast charging performance and cycle life. The results are shown in Table 2.

[0120] For ease of comparison, the contents of carboxylic acid ester solvents (a), methylene disulfonate (MMDS) (b), and transesterification rate of the negative electrode in lithium-ion batteries are listed in Table 2.

[0121] The fast charging time test method is as follows: Using the stepped fast charging method, the lithium-ion battery is charged at 0.33C to 10% SOC, then at 4.6C to 3.65V or 0V auxiliary voltage, then skips to the next step of charging at 4.2C to 3.65V or 0V auxiliary voltage, and then at 0.4C down-step to 80% SOC. The charging time from 10% to 80% SOC is calculated.

[0122] The high-temperature cycle life test method is as follows: At 60℃, the lithium-ion battery is cycled according to the following procedure: constant current charging at 1C rate to 3.65V, constant voltage charging until the current drops to 0.05C, rest for 30 minutes, discharge at 1C rate to 2.5V, and rest for 30 minutes; cycle according to the above procedure until the capacity of the lithium-ion battery is less than 80% of the initial capacity, and record the number of cycles.

[0123] Table 2

[0124]

[0125]

[0126] As shown in Table 2, the lithium-ion battery test results, referring to Examples 1-19, coordinately controlling the mass percentage content of carboxylic acid ester solvents, MMDS, and the transesterification rate of the negative electrode is beneficial for improving both the fast-charging performance and high-temperature cycle life of lithium-ion batteries. However, in Comparative Examples 1-4, when the values ​​of the relationship between the mass percentage content of carboxylic acid ester solvents, MMDS, and the transesterification rate of the negative electrode exceed the range of 0.01-64, it can be seen that both the fast-charging performance and high-temperature cycle life of the lithium-ion batteries show a significant decrease. This is because, by coordinating the numerical relationship of these three factors, the diffusion and transport of lithium ions in the electrolyte and the interfacial reaction between lithium ions and the negative electrode can be effectively regulated, thereby improving the fast-charging performance and high-temperature cycle life of the lithium-ion batteries. Furthermore, in Comparative Examples 3-4, when the values ​​of the relationship exceed the range of 0.01-64, if the content of carboxylic acid ester solvents, MMDS, and the transesterification rate of the negative electrode are not effectively controlled, the battery performance shows further deterioration.

[0127] Furthermore, in Examples 1-19, compared with other examples, the lithium-ion batteries provided in Examples 1-6 exhibit superior fast-charging performance and high-temperature cycle life. Comparing the results of Examples 1-9, in lithium-ion batteries, when the content of carboxylic acid ester solvents is too high, it causes electrolyte decomposition and gas production, reducing the battery's cycle life; when it is too low, it results in high electrolyte viscosity, hindering lithium-ion transport and thus reducing the battery's fast-charging performance. When the MMDS content is too high, it causes the SEI formed on the negative electrode to be too thick, increasing the interface impedance of the negative electrode and reducing the battery's fast-charging performance; when it is too low, the negative electrode cannot form a stable SEI film, increasing side reactions between the electrolyte and the negative electrode, consuming active lithium, and thus reducing the battery's cycle life. When the ester exchange rate of the negative electrode is too high, it increases side reactions between the electrolyte and the negative electrode, reducing the battery's cycle life; when it is too low, it reduces the lithium-ion insertion / extraction rate, reducing the battery's fast-charging performance. Comparing the results of Examples 10-19, it was found that a higher value in the formula relating the content of carboxylic acid ester solvents, MMDS, and the transesterification rate of the negative electrode further reduces the cycle life of the battery; conversely, a lower value results in poorer fast-charging performance. This demonstrates that precise and coordinated control of the numerical relationship between these three factors can improve the fast-charging and high-temperature cycling performance of lithium-ion batteries.

[0128] In summary, the lithium-ion battery provided by this invention synergistically regulates the amount of carboxylic acid ester solvent and additive methylene disulfonate in the electrolyte, as well as the ester exchange rate of the negative electrode. By comprehensively controlling the numerical relationship between the three, the fast charging capability and high-temperature cycle life of the lithium-ion battery are both improved.

[0129] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes at least a negative electrode and an electrolyte, wherein the electrolyte includes an organic solvent and additives; The organic solvent includes carboxylic acid ester solvents, and the additive includes methylene methane disulfonate; In the lithium-ion battery, the carboxylic acid ester solvent, methylene methane disulfonate, and the negative electrode sheet satisfy the following relationship: 0.01≤(a×c) / b≤64; Where a is the mass percentage of carboxylic acid ester solvent in the electrolyte, b is the mass percentage of methylene disulfonate in the electrolyte, and c is the transesterification rate of the negative electrode.

2. The lithium-ion battery according to claim 1, characterized in that, The carboxylic acid ester solvent, methylene methane disulfonate, and the negative electrode sheet satisfy the following condition: 0.5 ≤ (a × c) / b ≤ 9.

3. The lithium-ion battery according to claim 1, characterized in that, The electrolyte contains 5%-70% by mass of carboxylic acid ester solvents. And / or, the electrolyte contains 0.1%-1.5% methane disulfonate by mass. And / or, the transesterification rate of the negative electrode is 0.1%-10%.

4. The lithium-ion battery according to claim 3, characterized in that, The electrolyte contains 20%-60% by mass of carboxylic acid ester solvents. And / or, the electrolyte contains 0.3%-1% methylene disulfonate by mass; And / or, the transesterification rate of the negative electrode is 1%-5%.

5. The lithium-ion battery according to claim 1, characterized in that, The carboxylic acid ester solvents include C2-C8 carboxylic acid ester compounds.

6. The lithium-ion battery according to claim 5, characterized in that, The carboxylic acid ester solvent includes any one or a combination of at least two of ethyl acetate, ethyl propionate, methyl propionate, or methyl acetate.

7. The lithium-ion battery according to claim 1, characterized in that, The organic solvents also include carbonate solvents.

8. The lithium-ion battery according to claim 7, characterized in that, The carbonate solvents include any one or a combination of at least two of ethylene carbonate, ethyl methyl carbonate, or dimethyl carbonate.

9. The lithium-ion battery according to claim 7, characterized in that, The electrolyte contains 30%-80% carbonate solvent by mass.

10. The lithium-ion battery according to claim 1, characterized in that, The additives also include at least one of vinylene carbonate, fluoroethylene carbonate, or vinyl sulfite.

11. The lithium-ion battery according to claim 1, characterized in that, The negative electrode sheet includes a current collector and a negative electrode material layer coated on at least one side of the current collector; The compaction density of the negative electrode material layer is 1.2-1.8 g / cm³. 3 .

12. The lithium-ion battery according to claim 11, characterized in that, The porosity of the negative electrode material layer is 30%-50%.

13. The lithium-ion battery according to claim 11, characterized in that, The ionic conductivity of the negative electrode material layer is 0.1-1 mS / cm.

14. The lithium-ion battery according to claim 11, characterized in that, The negative electrode material layer includes a negative electrode active material; the negative electrode active material includes graphite and / or silicon-based materials.

15. The lithium-ion battery according to claim 14, characterized in that, The silicon-based material includes silicon-carbon and / or silicon-oxygen.

16. The lithium-ion battery according to claim 14, characterized in that, The particle size range of the silicon-based material is 50-300 nm.

17. The lithium-ion battery according to claim 14, characterized in that, The graphite includes primary particulate graphite and / or secondary particulate graphite.

18. The lithium-ion battery according to claim 17, characterized in that, The graphite in question contains 50%-100% by mass of secondary particulate graphite.

19. The lithium-ion battery according to claim 17, characterized in that, The primary graphite particles have a particle size of 1-15 μm, and the secondary graphite particles have a particle size of 6-20 μm.

20. An electrical device, characterized in that, The electrical device includes the lithium-ion battery according to any one of claims 1-19.

Images