WO2022111346A1 - 锂离子电池 - Google Patents

锂离子电池 Download PDF

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WO2022111346A1
WO2022111346A1 PCT/CN2021/131060 CN2021131060W WO2022111346A1 WO 2022111346 A1 WO2022111346 A1 WO 2022111346A1 CN 2021131060 W CN2021131060 W CN 2021131060W WO 2022111346 A1 WO2022111346 A1 WO 2022111346A1
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lithium
aqueous electrolyte
ion battery
carbonate
lithium ion
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PCT/CN2021/131060
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English (en)
French (fr)
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钱韫娴
胡时光
李红梅
员晓刚
邓永红
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深圳新宙邦科技股份有限公司
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Priority to EP21896847.7A priority Critical patent/EP4254582A1/en
Priority to US18/036,400 priority patent/US20230402653A1/en
Publication of WO2022111346A1 publication Critical patent/WO2022111346A1/zh

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    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C265/00—Derivatives of isocyanic acid
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    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2601/00—Systems containing only non-condensed rings
    • C07C2601/12—Systems containing only non-condensed rings with a six-membered ring
    • C07C2601/14—The ring being saturated
    • H—ELECTRICITY
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    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0037—Mixture of solvents
    • 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 invention relates to the technical field of lithium ion batteries, in particular to a lithium iron phosphate battery.
  • Lithium-ion batteries are widely used in production and life due to their excellent performance. In recent years, with the continuous improvement of the cruising range requirements of new energy vehicles, people have put forward higher requirements for the cycle life and safety of lithium-ion batteries.
  • lithium iron phosphate batteries Compared with ternary batteries, lithium iron phosphate batteries have more advantages in terms of cycle life, safety and cost, but the energy density of lithium iron phosphate is still far from that of ternary materials. Compaction density and areal density are one of the important means to improve the energy density of lithium iron phosphate batteries, but the lower the porosity of the pole piece, the higher the requirements for the electrolyte: first, when the porosity is low, it is difficult for the electrolyte to penetrate into the electrode.
  • the liquid retention amount during the battery production is insufficient, which further leads to a significant decrease in the cycle performance of the battery, and there is also the problem of lithium precipitation; secondly, the insufficient liquid retention amount will also lead to an increase in the contact internal resistance between the electrolyte and the pole piece. , affecting the battery capacity and rate discharge performance.
  • the purpose of the present invention is to overcome the problems of poor high temperature performance and serious gas swelling of high-pressure lithium iron phosphate batteries in the prior art, and to provide a lithium ion battery, which has high temperature cycle, good storage performance, etc. advantage.
  • the present invention provides a lithium ion battery
  • the lithium ion battery includes a positive electrode, a negative electrode, a separator placed between the positive electrode and the negative electrode, and a non-aqueous electrolyte
  • the active material of the positive electrode contains LiFePO 4
  • the non-aqueous electrolyte solution contains an organic solvent, a lithium salt, vinylene carbonate, and a compound represented by the formula (1):
  • R 1 is one or more of chain, cyclic and aromatic groups of 2-20 carbon atoms, wherein the compaction density of the positive electrode material is 2 g/cm 3 or more.
  • the R 1 is one or more of chain, cyclic and aromatic groups of 3-18 carbon atoms.
  • R 1 is selected from one or more of the following structures, wherein * represents the position of binding:
  • the compound represented by the formula (1) is selected from one or more of the following compounds:
  • the content of the compound represented by formula (1) is 0.001-5% by weight; more preferably, in the non-aqueous electrolyte, the non-aqueous electrolyte is The content of the compound represented by formula (1) is 0.001-3 wt % based on the total weight of the aqueous electrolyte.
  • the content of the vinylene carbonate is 0.1-5% by weight; more preferably, in the non-aqueous electrolyte, the amount of non-aqueous Based on the total weight of the electrolyte, the content of the vinylene carbonate is 0.5-3% by weight.
  • the organic solvent is one or more of cyclic carbonate, linear carbonate, carboxylate and ether.
  • the cyclic carbonate includes one or more of vinylene carbonate, propylene carbonate and ethylene carbonate.
  • the linear carbonate includes one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.
  • the carboxylic acid esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethyl acetate and ethyl trimethyl acetate one or more of the esters.
  • the ethers include ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether one or more of.
  • the organic solvent is a mixture of ethylene carbonate and ethyl methyl carbonate.
  • the lithium salt is LiPF 6 , LiBF 4 , LiBOB, LiDFOB, LiPO 2 F 2 , LiSbF 6 , LiAsF 6 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 C 2 F 5 ) 2 , LiC One or more of (SO 2 CF 3 ) 3 and LiFSI; more preferably, the lithium salt is one or more of LiPF 6 , LiPO 2 F 2 and LiFSI.
  • the content of the lithium salt is 0.1-2 mol/L; more preferably, in the non-aqueous electrolyte, the content of the lithium salt is 0.8-1.5 mol/L.
  • the non-aqueous electrolyte further contains other additives, and the other additives are 1,3-propane sultone, 1,4-butane sultone, methylene methanedisulfonate, fluoro Vinyl Carbonate, 1,3-Propane Sultone, Vinyl Sulfate, Methylene Methylene Disulfonate, Lithium Difluorophosphate, Lithium Difluorooxalate Borate, Tris(trimethylsilane) Phosphate, Propylene Sulfonic Acid one or more of lactone, fluorobenzene and vinyl ethylene carbonate; more preferably, the other additives are one or more of lithium difluorophosphate, vinyl sulfate and methylene disulfonate kind.
  • the other additives are 1,3-propane sultone, 1,4-butane sultone, methylene methanedisulfonate, fluoro Vinyl Carbonate, 1,3-Propane Sultone,
  • the content of the other additives is 0.1-5% by weight; more preferably, in the non-aqueous electrolyte, the non-aqueous electrolyte is Based on the total weight, the content of the other additives is 0.1-3% by weight.
  • the compaction density of the positive electrode material is 2-3 g/cm 3 .
  • the compacted density of the negative electrode material is 1.3 g/cm 3 or more; more preferably, the compacted density of the negative electrode material is 1.3-1.8 g/cm 3 .
  • the voltage range of the lithium ion battery is 2-4V; more preferably, the voltage range of the lithium ion battery is 2-3.65V.
  • the liquid injection coefficient of the lithium ion battery is 2-7 g/Ah; more preferably, the liquid injection coefficient of the lithium ion battery is 3-5 g/Ah.
  • the cycle and storage performance of the lithium iron phosphate battery at high temperature can be significantly improved, the capacity retention rate and the capacity recovery rate of the battery can be greatly improved, and the thickness expansion rate of the lithium iron phosphate battery after high temperature storage can be significantly reduced, and At the same time, the dissolution of iron ions can be greatly reduced.
  • Fig. 1 is the SEM image of the negative electrode of the lithium ion battery prepared in Example 7 of the present invention which is cycled 2500 times at 45°C;
  • FIG. 2 is a SEM image of the negative electrode of the lithium ion battery prepared in Comparative Example 1 of the present invention at 45° C. for 2500 cycles.
  • the present invention provides a lithium ion battery
  • the lithium ion battery includes a positive electrode, a negative electrode, a separator placed between the positive electrode and the negative electrode, and a non-aqueous electrolyte
  • the active material of the positive electrode contains LiFePO 4
  • the non-aqueous electrolyte contains Organic solvent, lithium salt, vinylene carbonate and compound represented by formula (1):
  • R 1 is one or more of chain, cyclic and aromatic groups of 2-20 carbon atoms, wherein the compaction density of the positive electrode material is 2 g/cm 3 or more.
  • the inventors of the present invention have found through extensive research and experiments that, in a lithium ion battery in which the positive electrode active material contains LiFePO 4 , when the non-aqueous electrolyte of the lithium ion battery contains both vinylene carbonate (VC) and a compound represented by formula (1)
  • the compound is used, within the range of the compaction density of the positive electrode material defined in the present invention, the cycle and storage performance of the lithium iron phosphate battery at high temperature can be significantly improved, and the volume expansion rate of the lithium iron phosphate battery after high temperature storage can be greatly reduced. It can reduce the dissolution of iron ions.
  • the reason may be due to the dissolution of iron ions in the positive electrode material in the lithium iron phosphate battery system, and the dissolved iron ions will be deposited on the surface of the negative electrode, blocking the channels for the insertion or extraction of lithium ions, resulting in the rate of insertion or extraction of lithium ions on the surface of the negative electrode. It is obviously reduced, so that lithium dendrites are formed on the surface of the negative electrode. The reaction between lithium dendrites and the electrolyte consumes the electrolyte and also generates a large amount of gas, which makes the battery volume expand, and in severe cases, it will cause the battery to cycle diving and high-pressure compaction.
  • the iron ion dissolution phenomenon is more serious, and adding the compound represented by the formula (1) can play a complexation effect on the iron ion, and through the synergistic effect with vinylene carbonate, within the range of the positive electrode compaction density defined in the present invention, the iron ion can be inhibited.
  • the dissolution of ions from the positive electrode and the deposition on the negative electrode can reduce the occurrence of side reactions and the loss of electrolyte, thereby significantly improving the high temperature cycling and storage performance of the battery.
  • the R 1 is one or more of chain, cyclic and aromatic groups of 3-18 carbon atoms; more preferably, the R 1 is selected from one or more of the following structures, wherein * represents the position of binding (ie, the atom to which the N atom in formula (1) is attached):
  • the compound represented by the formula (1) is selected from one or more of the following compounds:
  • the content of the compound represented by formula (1) in the non-aqueous electrolyte solution, can vary within a wide range, for example, based on the total weight of the non-aqueous electrolyte solution, its content can be 0.001-5% by weight ;
  • the content of the compound represented by formula (1) is 0.001-3% by weight.
  • the performance of the battery can be significantly improved.
  • the content of the compound should not exceed 5% by weight, because when the content of the compound represented by formula (1) in the non-aqueous electrolyte is higher than 5% by weight, the performance of the lithium-ion battery will not be further improved, On the contrary, it may be adversely affected, because the excessive amount of the compound represented by formula (1) will increase the side reactions inside the battery, consume the content of active lithium, make the SEI film formed by the negative electrode too thick, increase the battery impedance, and deteriorate the battery cycle. performance.
  • the content of the vinylene carbonate can be determined according to the total weight of the non-aqueous electrolyte, for example, in the non-aqueous electrolyte, based on the total weight of the non-aqueous electrolyte, the vinylene carbonate
  • the content is 0.1-5% by weight; preferably, in the non-aqueous electrolyte, based on the total weight of the non-aqueous electrolyte, the content of the vinylene carbonate is 0.5-3% by weight; more preferably, the non-aqueous electrolyte In the aqueous electrolyte, based on the total weight of the non-aqueous electrolyte, the content of the vinylene carbonate is 1-3% by weight.
  • the content of the vinylene carbonate is lower than this range, the effect is not obvious; when the content of the vinylene carbonate is higher than this range, the internal resistance of the battery will be increased and the cycle performance of the battery will be deteriorated.
  • the organic solvent in the non-aqueous electrolyte of the lithium ion battery can be various organic solvents commonly used in the field to prepare non-aqueous electrolytes, and is not particularly limited.
  • the organic solvent can be selected from cyclic One or more of carbonate, linear carbonate and carboxylate.
  • the cyclic carbonate used for non-aqueous electrolysis of lithium ion batteries may include: one or more of vinylene carbonate, propylene carbonate and ethylene carbonate.
  • the linear carbonate used for non-aqueous electrolysis of lithium ion batteries may include one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.
  • the carboxylate used for non-aqueous electrolysis of lithium ion batteries may include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, and methyl trimethyl acetate and one or more of ethyl trimethylacetate.
  • the ethers used for non-aqueous electrolysis of lithium ion batteries may include ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3 - one or more of tetrafluoropropyl ether.
  • the organic solvent is a mixture of ethylene carbonate and ethyl methyl carbonate.
  • the non-aqueous electrolyte can have a higher dielectric constant and a lower viscosity, thereby improving the overall performance of the battery.
  • the lithium salt in the non-aqueous electrolyte of the lithium ion battery can use various lithium salts commonly used in the preparation of lithium ion batteries in the art, without special limitation, for example, LiPF 6 , LiBF 4 , LiBOB, LiDFOB can be selected one or more of , LiPO 2 F 2 , LiSbF 6 , LiAsF 6 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 C 2 F 5 ) 2 , LiC(SO 2 CF 3 ) 3 and LiFSI;
  • the lithium salt is one or more of LiPF 6 , LiPO 2 F 2 and LiFSI; more preferably, the lithium salt is LiPF 6 .
  • the electrochemical stability, electrical conductivity, and graphite anode compatibility of the non-aqueous electrolyte can be improved.
  • the content of the lithium salt may be the usual content in lithium ion batteries in the art, and is not particularly limited.
  • the content of the lithium salt in the non-aqueous electrolyte of the lithium ion battery is 0.1-2 mol/L; preferably, the content of the lithium salt in the non-aqueous electrolyte of the lithium ion battery is 0.8-1.5 mol/L; more preferably, the content of the lithium salt in the non-aqueous electrolyte of the lithium ion battery is 0.8-1.2 mol/L.
  • the non-aqueous electrolyte solution can have better viscosity and conductivity.
  • the non-aqueous electrolyte for lithium ion batteries may further contain various other additives commonly used in the art to improve the performance of lithium ion batteries, such as: 1, 3-Propane Sultone, 1,4-Butane Sultone, Methylene Methanedisulfonate, Fluoroethylene Carbonate, 1,3-Propane Sultone, Vinyl Sulfate, Methylene Disulfonic Acid One or more of methyl ester, lithium difluorophosphate, lithium difluorooxalate borate, tris(trimethylsilane) phosphate, propylene sultone, fluorobenzene and vinyl ethylene carbonate; preferably, the The other additives are one or more of lithium difluorophosphate, vinyl sulfate and methylene methanedisulfonate. When the other additives mentioned above are added, the high temperature storage and cycling performance of the battery can be further improved.
  • the content of the other additives may be the conventional content of various additives in the field of lithium ion batteries.
  • the content of the other additives may be 0.1-5 wt % of the total weight of the non-aqueous electrolyte of the lithium ion battery; preferably, the content of the additive may be 0.1-5 wt % of the total weight of the non-aqueous electrolyte of the lithium ion battery 0.1-3 wt %; more preferably, the content of the additive may be 0.3-1 wt % of the total weight of the non-aqueous electrolyte of the lithium ion battery.
  • the active material of the positive electrode of the lithium ion battery is LiFePO 4 .
  • the active material of the negative electrode can be selected from various materials commonly used in the negative electrode active material of lithium ion batteries in the art, without special limitation, for example, it can be metal lithium, graphite-like carbon materials, hard carbon materials, soft carbon materials, silicon-based, One or more of tin-based, antimony-based, aluminum-based, transition metal compounds, silicon carbon materials and silicon oxycarbon; preferably, the active material of the negative electrode is artificial graphite, natural graphite, modified natural graphite and silicon one or more of oxycarbons.
  • the preparation of the positive electrode and the negative electrode of the lithium ion battery can be carried out according to the method commonly used in the art for preparing the positive electrode and the negative electrode of the lithium ion battery, and there is no particular limitation.
  • the active materials of the positive and negative electrodes can be mixed with a conductive agent and a binder, and the mixture can be dispersed in an organic solvent to prepare a slurry, and then the obtained slurry can be coated on a current collector and dried and rolled, etc. deal with.
  • the conductive agent, adhesive, organic solvent, current collector, etc. used can all be materials and substances commonly used in the art, which will not be repeated here.
  • the compaction density of the positive electrode material is 2-3 g/cm 3 .
  • the compaction density of the negative electrode material may be above 1.3 g/cm 3 , preferably, the compaction density of the negative electrode material is 1.3-1.8 g/cm 3 .
  • the voltage range of the lithium ion battery may be 2-4V; preferably, the voltage range of the lithium ion battery is 2-3.65V.
  • the liquid injection coefficient of the lithium ion battery is 2-7 g/Ah; preferably, the liquid injection coefficient of the lithium ion battery is 3-5 g/Ah. This not only ensures that the battery has good high-temperature cycle and storage performance, but also reduces the use of electrolyte, thereby saving battery production costs.
  • the separator placed between the positive electrode and the negative electrode can be various materials commonly used as separators in the field, without particular limitation, for example, can be polyolefin separators, polyamide separators, polysulfone separators , one or more of polyphosphazene type diaphragm, polyether sulfone type diaphragm, polyether ether ketone type diaphragm, polyether amide type diaphragm and polyacrylonitrile type diaphragm.
  • the separator is selected from polyethylene separators, and is a polyethylene microporous membrane.
  • the preparation of the lithium ion battery can be carried out by the "sandwich" method commonly used in the art.
  • a separator is placed between the positive electrode sheet and the negative electrode sheet coated with the active material, and then the whole is wound, Then, the coiled body is flattened and placed in a packaging bag to be vacuum-baked and dried to obtain a battery cell. Then, the electrolyte is injected into the battery core, vacuum-sealed and left to stand for formation.
  • This method is a well-known method in the art, and will not be repeated here.
  • the cathode active material LiFePO 4 was purchased from Shenzhen Defang Nanotechnology Co., Ltd., model DY-3.
  • test methods of each performance in the following examples and comparative examples are carried out according to the following test examples:
  • Test Example 1 High temperature cycle performance test
  • the lithium-ion batteries prepared in the following examples and comparative examples were placed in an oven with a constant temperature of 45°C, charged to 3.65V with a constant current of 1C, and then charged at a constant voltage until the current dropped to 0.1C, and then charged with a constant current of 1C. Discharge to 2.0V, cycle 2500 times, record the discharge capacity of the 1st and 2500th times, and calculate the capacity retention rate of high temperature cycle as follows:
  • Capacity retention rate (%) discharge capacity at the 2500th cycle/discharge capacity at the first cycle ⁇ 100%.
  • the lithium-ion batteries prepared in the following examples and comparative examples were charged to 3.65V with 1C constant current and constant voltage at room temperature, and then charged with constant voltage until the current dropped to 0.1C, and the initial discharge capacity and initial battery volume of the battery were measured, and then at 60 After 30 days of storage in the environment of °C, discharge to 2.0V at 1C, measure the retention capacity and recovery capacity of the battery at this time and the battery volume after storage, and calculate the battery capacity retention rate, capacity recovery rate and volume expansion rate.
  • the calculation formulas are as follows:
  • Capacity retention rate (%) retention capacity / initial discharge capacity ⁇ 100%;
  • Capacity recovery rate (%) recovery capacity/initial discharge capacity ⁇ 100%
  • Volume expansion rate (%) (battery volume after storage-initial battery volume)/initial battery volume ⁇ 100%.
  • Disassemble the battery after 2500 cycles take out the negative electrode of the battery and the negative electrode side diaphragm, and place it in a mixed solution of HNO 3 (concentration of 14.5 mol/L) and H 2 O (mixed at a weight ratio of 1:2) dissolved in. After the digestion was complete, 20 g of the digestion solution was dispensed into 50 mL reagent bottles, and then the amount of iron ions dissolved on the negative electrode and the separator was tested by inductively coupled plasma optical emission spectrometer (ICP-OES).
  • ICP-OES inductively coupled plasma optical emission spectrometer
  • Compound 1 with a total weight of 0.001% by weight of the liquid (Note: Compound 1 here is Compound 1 in the specification, the same below) and VC with a total weight of the electrolyte of 2% by weight;
  • the positive active material LiFePO 4 , the conductive agent conductive carbon black Super-P, and the binder polyvinylidene fluoride (PVDF) were uniformly mixed in a weight ratio of 93:4:3, and then dispersed in N-methyl-2 - In pyrrolidone (NMP), the positive electrode slurry is obtained; the positive electrode slurry is uniformly coated on both sides of the aluminum foil, dried, rolled (compacted density as shown in Table 1) and vacuum dried, and welded with an ultrasonic welder.
  • the positive plate is obtained after the aluminum lead wire, and the thickness of the plate is 100 ⁇ 2 ⁇ m;
  • the negative active material modified natural graphite, the conductive agent conductive carbon black Super-P, and the binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are mixed uniformly in a weight ratio of 95:1:2.5:1.5, Then the mixture was dispersed in deionized water to obtain negative electrode slurry; the negative electrode slurry was coated on both sides of the copper foil, dried, rolled (compacted density as shown in Table 1) and vacuum dried, and then used an ultrasonic welder Negative plates are obtained after welding nickel lead wires, and the thickness of the plates is 120 ⁇ 2 ⁇ m;
  • a three-layer separator (Xingyuan material, 12+2+2um ceramic PP separator) with a thickness of 20 ⁇ m is placed between the positive plate and the negative plate, and then the sandwich structure composed of the positive plate, the negative plate and the separator is wound. Squeeze the winding body and put it into an aluminum foil packaging bag, and bake it in a vacuum at 75°C for 48 hours to obtain the cell to be injected;
  • step 1) inject the electrolyte prepared in step 1) into the battery cell prepared in step 4), where the injection coefficient is 4g/Ah, and then perform the routine formation of the first charge according to the following steps : 0.05C constant current charge for 180min, 0.1C constant current charge for 180min, rest for 24hrs, shape and seal, then further charge to 3.65V with 0.2C constant current, after 24hrs at room temperature, discharge with 0.2C constant current to 2.0V.
  • Example 1 Following the method of Example 1, except that the compaction density of the positive and negative electrode materials of the lithium ion battery, the type and addition amount of the compound represented by formula (1) added to the electrolyte, the addition amount of VC, and other additives The type and the amount of added are different, and the specific content is shown in Table 1.
  • LiPO 2 F 2 is lithium difluorophosphate
  • DTD is vinyl sulfate
  • MMDS is methylene methane disulfonate.
  • Example 7 Example 10-11, Comparative Example 1 and Comparative Example 5-6 that under the compaction density of the positive electrode material defined in the present invention, adding VC and formula ( The compounds represented by 1) can significantly improve the high temperature cycling and storage performance of Li-ion batteries.
  • the compound represented by formula (1) is The addition amount in the electrolyte is between 0.001-5 wt %, which can effectively improve the high temperature storage and cycle performance of the battery; when the content is 0.5 wt %, the improvement of battery performance is the best; when the content is less than 0.5 wt % When the content is more than 0.5 wt%, the residual amount in the pole piece is also increased, and the excess of the compound represented by formula (1) will increase The side reactions inside the battery are not conducive to the improvement of battery performance such as cycling.
  • Example 7 Example 16-18, Comparative Example 1 and Comparative Example 2-4, it can be seen that under the compaction density of the positive electrode material defined in the present invention, by adding formula to the non-aqueous electrolyte of lithium ion battery
  • the compound represented by (1), and adding additives such as LiPO 2 F 2 , DTD and MMDS to the non-aqueous electrolyte of lithium-ion batteries can further improve the high-temperature cycling and storage performance of lithium-ion batteries, but not in non-aqueous electrolytes.
  • the compound represented by the formula (1) is added, even if other additives are added, the high temperature cycle and storage performance of the lithium ion battery cannot be significantly improved.
  • Fig. 1 is the SEM image of the negative electrode of the lithium-ion battery prepared in Example 7 of the present invention at 45°C for 2500 cycles
  • Fig. 2 is the SEM image of the negative electrode of the lithium-ion battery prepared in Comparative Example 1 of the present invention cycled at 45°C for 2500 times.

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Abstract

本发明涉及锂离子电池技术领域，公开了一种锂离子电池。该锂离子电池包括正极、负极、置于正极与负极之间的隔膜以及非水电解液，所述正极的活性材料含有LiFePO 4；所述非水电解液含有有机溶剂、锂盐、碳酸亚乙烯酯和式(1)表示的化合物，式(1)中，式(1)中，R 1为2-20个碳原子的链状、环状和芳香基团中的一种或多种，正极材料的压实密度为2g/cm 3以上。本发明提供的锂离子电池可以显著改善高温下的循环和存储性能，大幅提高电池的容量保持率和容量恢复率，并明显降低高温存储后的厚度膨胀率，并且同时可以大大降低铁离子的溶出。

Description

锂离子电池 技术领域
本发明涉及锂离子电技术领域，具体涉及一种磷酸铁锂电池。
背景技术
锂离子电池因其优良的性能广泛应用于生产生活中，近年来，随着新能源汽车续航里程要求的不断提高，人们对锂离子电池的循环寿命和安全性提出了更高的要求。
与三元电池相比，磷酸铁锂电池在循环寿命、安全性和成本方面更具优势，但是磷酸铁锂的能量密度与三元材料相比仍有较大差距，提高电池正负极片的压实密度和面密度是提高磷酸铁锂电池能量密度的重要手段之一，但是极片孔隙率越低，对电解液的要求也就越高：首先孔隙率低时电解液很难渗透到极片内部，致使电池制作时的保液量不足，进一步导致电池的循环性能明显衰减，且同时还存在析锂问题；其次保液量不足也会导致电解液和极片间的接触内阻变大，影响电池容量及倍率放电性能。
一般而言，开发适用于高压实极片的电解液的方向主要有两种：一种是使用含低粘度的溶剂，以促进电解液浸润，提高电池的循环、倍率等性能；另一种是添加降低阻抗、促进循环的添加剂，从而提高电池的使用寿命。但是这两种方法都会在一定程度上导致电解液的高温性能变差，同时气胀现象也比较严重。所以，在保证电池不析锂的同时，如何改善电池的高温循环和高温存储性能，是高压实磷酸铁锂电池电解液面临的一个难题。
发明内容
本发明的目的是为了克服现有技术存在的高压实磷酸铁锂电池高温性 能不佳和气胀现象严重的问题，提供一种锂离子电池，该锂离子电池具有高温下循环、存储性能良好等优点。
为了实现上述目的，本发明提供一种锂离子电池，该锂离子电池包括正极、负极、置于正极与负极之间的隔膜以及非水电解液，所述正极的活性材料含有LiFePO 4，所述非水电解液含有有机溶剂、锂盐、碳酸亚乙烯酯和式(1)表示的化合物：
Figure PCTCN2021131060-appb-000001
式(1)中，R 1为2-20个碳原子的链状、环状和芳香基团中的一种或多种，，其中，正极材料的压实密度为2g/cm 3以上。
优选地，式(1)中，所述R 1为3-18个碳原子的链状、环状和芳香基团中的一种或多种。
更优选地，所述R 1选自以下结构中的一种或多种，其中，*表示结合的位置：
Figure PCTCN2021131060-appb-000002
优选地，所述式(1)表示的化合物选自以下化合物中的一种或多种：
Figure PCTCN2021131060-appb-000003
优选地，所述非水电解液中，以非水电解液总重量计，式(1)表示的化合物的含量为0.001-5重量％；更优选地，所述非水电解液中，以非水电解液总重量计，式(1)表示的化合物的含量为0.001-3重量％。
优选地，所述非水电解液中，以非水电解液总重量计，所述碳酸亚乙烯 酯的含量为0.1-5重量％；更优选地，所述非水电解液中，以非水电解液总重量计，所述碳酸亚乙烯酯的含量为0.5-3重量％。
优选地，所述有机溶剂为环状碳酸酯、线状碳酸酯、羧酸酯和醚类中的一种或多种。
优选地，所述环状碳酸酯包括碳酸亚乙烯酯、碳酸丙烯酯和碳酸乙烯酯中的一种或多种。
优选地，所述线状碳酸酯包括碳酸二甲酯、碳酸二乙酯和碳酸甲乙酯中的一种或多种。
优选地，所述羧酸酯包括醋酸甲酯、醋酸乙酯、丙酸甲酯、丙酸乙酯、丁酸甲酯、异丁酸甲酯、三甲基乙酸甲酯和三甲基乙酸乙酯中的一种或多种。
优选地，所述醚类包括乙二醇二甲醚、1,3-二氧戊环和1,1,2,2-四氟乙基-2,2,3,3-四氟丙基醚中的一种或多种。
更优选地，所述有机溶剂为碳酸乙烯酯和碳酸甲乙酯的混合物。
优选地，所述锂盐为LiPF 6、LiBF 4、LiBOB、LiDFOB、LiPO 2F 2、LiSbF 6、LiAsF 6、LiN(SO 2CF 3) 2、LiN(SO 2C 2F 5) 2、LiC(SO 2CF 3) 3和LiFSI中的一种或多种；更优选地，所述锂盐为LiPF 6、LiPO 2F 2和LiFSI中的一种或多种。
优选地，所述非水电解液中，所述锂盐的含量为0.1-2mol/L；更优选地，所述非水电解液中，所述锂盐的含量为0.8-1.5mol/L。
优选地，所述非水电解液中，进一步含有其他添加剂，所述其他添加剂为1,3-丙烷磺内酯、1,4-丁烷磺内酯、甲烷二磺酸亚甲酯、氟代碳酸乙烯酯、1,3-丙磺内酯、硫酸乙烯酯、甲基二磺酸亚甲酯、二氟磷酸锂、二氟草酸硼酸锂、三(三甲基硅烷)磷酸酯、丙烯磺酸内酯、氟苯和乙烯基碳酸乙烯酯中的一种或多种；更优选地，所述其他添加剂为二氟磷酸锂、硫酸乙烯酯和甲烷二磺酸亚甲酯中的一种或多种。
优选地，所述非水电解液中，以非水电解液总重量计，所述其他添加剂 的含量为0.1-5重量％；更优选地，所述非水电解液中，以非水电解液总重量计，所述其他添加剂的含量为0.1-3重量％。
优选地，所述正极材料的压实密度为2-3g/cm 3。
优选地，负极材料的压实密度为1.3g/cm 3以上；更优选地，所述负极材料的压实密度为1.3-1.8g/cm 3。
优选地，所述锂离子电池的电压区间为2-4V；更优选地，所述锂离子电池的电压区间为2-3.65V。
优选地，所述锂离子电池的注液系数为2-7g/Ah；更优选地，所述锂离子电池的注液系数为3-5g/Ah。
通过上述技术方案，可以显著改善磷酸铁锂电池在高温下的循环和存储性能，大幅提高电池的容量保持率和容量恢复率，并明显降低磷酸铁锂电池在高温存储后的厚度膨胀率，并且同时可以大大降低铁离子的溶出。
附图说明
图1是本发明实施例7制备的锂离子电池在45℃下循环2500次的负极SEM图；
图2是本发明对比例1制备的锂离子电池在45℃下循环2500次的负极SEM图。
具体实施方式
在本文中所披露的范围的端点和任何值都不限于该精确的范围或值，这些范围或值应当理解为包含接近这些范围或值的值。对于数值范围来说，各个范围的端点值之间、各个范围的端点值和单独的点值之间，以及单独的点值之间可以彼此组合而得到一个或多个新的数值范围，这些数值范围应被视为在本文中具体公开。
本发明提供一种锂离子电池，该锂离子电池包括正极、负极、置于正极与负极之间的隔膜以及非水电解液，所述正极的活性材料含有LiFePO 4，所述非水电解液含有有机溶剂、锂盐、碳酸亚乙烯酯和式(1)表示的化合物：
Figure PCTCN2021131060-appb-000004
式(1)中，R 1为2-20个碳原子的链状、环状和芳香基团中的一种或多种，其中，正极材料的压实密度为2g/cm 3以上。
本发明的发明人通过大量的研究和试验发现，在正极活性材料含有LiFePO 4的锂离子电池中，当锂离子电池非水电解液同时含有碳酸亚乙烯酯(VC)和式(1)表示的化合物时，在本发明限定的正极材料压实密度范围内，可以显著改善磷酸铁锂电池在高温下的循环和存储性能，并大大降低磷酸铁锂电池在高温存储后的体积膨胀率，同时还可以降低铁离子的溶出。
究其原因，可能是由于磷酸铁锂电池体系中正极材料存在铁离子溶出，溶出的铁离子会沉积在负极表面，堵塞锂离子嵌入或者脱出的通道，导致锂离子在负极表面的嵌入或脱出速率明显降低，从而在负极表面形成锂枝晶，锂枝晶和电解液反应消耗电解液的同时也会生成大量的气体，使电池体积膨胀，且严重时还会造成电池的循环跳水，高压实下铁离子溶出现象更加严重，而加入式(1)表示的化合物可以对铁离子起到络合作用，通过与碳酸亚乙烯酯协同作用，在本发明限定的正极压实密度范围内，抑制铁离子从正极的溶出及在负极的沉积，减少副反应的发生和电解液的损失，从而显著改善电池的高温循环和存储性能。
根据本发明，优选地，式(1)中，所述R 1为3-18个碳原子的链状、环状和芳香基团中的一种或多种；更优选地，所述R 1选自以下结构中的一种或多种，其中，*表示结合的位置(也即，与式(1)中的N原子连接的原子)：
Figure PCTCN2021131060-appb-000005
本发明中，优选地，所述式(1)表示的化合物选自以下化合物中的一种或多种：
Figure PCTCN2021131060-appb-000006
Figure PCTCN2021131060-appb-000007
本发明中，在所述非水电解液中，式(1)表示的化合物的含量可以在较大范围内变动，例如，以非水电解液总重量计，其含量可以为0.001-5重量％；优选地，在所述非水电解液中，以非水电解液总重量计，式(1)表示的化合物的含量为0.001-3重量％。
在本发明锂离子电池的非水电解液中，只要含有极少的由式(1)表示的化合物即可显著实现改善电池的性能，为进一步提高效果，还可以适当增加由式(1)表示的化合物的含量，但不宜超过5重量％，这是因为，当式(1)表示的化合物在非水电解液中的含量高于5重量％时，锂离子电池的性能不仅不会进一步提升，反而还可能受到不良影响，这是因为过量的式(1)表示的化合物会增加电池内部的副反应，消耗活性锂的含量，使得负极形成的SEI膜过厚，增加电池阻抗，劣化电池循环等性能。
本发明中，所述碳酸亚乙烯酯的含量可以根据非水电解液的总重量来决定，例如，所述非水电解液中，以非水电解液总重量计，所述碳酸亚乙烯酯的含量为0.1-5重量％；优选地，所述非水电解液中，以非水电解液总重量计，所述碳酸亚乙烯酯的含量为0.5-3重量％；更优选地，所述非水电解液中，以非水电解液总重量计，所述碳酸亚乙烯酯的含量为1-3重量％。当所述碳酸亚乙烯酯的含量低于此范围时，效果不明显；当所述碳酸亚乙烯酯的含量高于此范围时，会导致增大电池的内阻从而劣化电池的循环性能。
本发明中，所述锂离子电池非水电解液中的有机溶剂可以为本领域常用于制备非水电解液的各种有机溶剂，没有特别地限定，例如，所述有机溶剂可以选自环状碳酸酯、线状碳酸酯和羧酸酯中的一种或多种。
作为锂离子电池非水电解的所述环状碳酸酯可以包括：碳酸亚乙烯酯、碳酸丙烯酯和碳酸乙烯酯中的一种或多种。
作为锂离子电池非水电解的所述线状碳酸酯可以包括碳酸二甲酯、碳酸二乙酯和碳酸甲乙酯中的一种或多种。
作为锂离子电池非水电解的所述羧酸酯可以包括醋酸甲酯、醋酸乙酯、丙酸甲酯、丙酸乙酯、丁酸甲酯、异丁酸甲酯、三甲基乙酸甲酯和三甲基乙酸乙酯中的一种或多种。
作为锂离子电池非水电解的所述醚类可以包括乙二醇二甲醚、1,3-二氧戊环和1,1,2,2-四氟乙基-2,2,3,3-四氟丙基醚中的一种或多种。
在本发明一个优选的实施方式中，所述有机溶剂为所述有机溶剂为碳酸乙烯酯和碳酸甲乙酯的混合物。当所述有机溶剂为碳酸乙烯酯和碳酸甲乙酯的混合物时，可以使非水电解液拥有较高的介电常数和较低的粘度，从而改善电池的综合性能。
根据本发明，所述锂离子电池非水电解液中的锂盐可以使用本领域常用于制备锂离子电池的各种锂盐，没有特别的限定，例如可以选择LiPF 6、LiBF 4、LiBOB、LiDFOB、LiPO 2F 2、LiSbF 6、LiAsF 6、LiN(SO 2CF 3) 2、LiN(SO 2C 2F 5) 2、LiC(SO 2CF 3) 3和LiFSI中的一种或多种；优选地，所述锂盐为LiPF 6、LiPO 2F 2和LiFSI中的一种或多种；更优选地，所述锂盐为LiPF 6。当使用上述锂盐时，可以改善非水电解液的电化学稳定性、电导率和石墨负极相容性。
本发明中，所述锂盐的含量可以为本领域锂离子电池中的通常含量，没有特别的限定。本发明中，所述锂离子电池非水电解液中所述锂盐的含量为0.1-2mol/L；优选地，所述锂离子电池非水电解液中所述锂盐的含量为0.8-1.5mol/L；更优选地，所述锂离子电池非水电解液中所述锂盐的含量为0.8-1.2mol/L。当所述锂盐的含量在此范围内时，可以使非水电解液具有较好的粘度和电导率。
本发明中，锂离子电池非水电解液除含有式(1)表示的化合物和碳酸亚乙烯酯以外，还可以进一步含有本领域常用于提高锂离子电池性能的各种其他添加剂，例如：1,3-丙烷磺内酯、1,4-丁烷磺内酯、甲烷二磺酸亚甲酯、氟代碳酸乙烯酯、1,3-丙磺内酯、硫酸乙烯酯、甲基二磺酸亚甲酯、二氟磷酸锂、二氟草酸硼酸锂、三(三甲基硅烷)磷酸酯、丙烯磺酸内酯、氟苯和乙烯基碳酸乙烯酯中的一种或多种；优选地，所述其他添加剂为二氟磷酸锂、硫酸乙烯酯和甲烷二磺酸亚甲酯中的一种或多种。当添加上述其他添加剂时，可以进一步改善电池的高温存储和循环性能。
本发明中，所述其他添加剂的含量可以为本领域各种添加剂在锂离子电池中的常规含量。例如，所述其他添加剂的含量可以为所述锂离子电池非水电解液总重量的0.1-5重量％；优选地，所述添加剂的含量可以为所述锂离子电池非水电解液总重量的0.1-3重量％；更优选地，所述添加剂的含量可以为所述锂离子电池非水电解液总重量的0.3-1重量％。
根据本发明，所述锂离子电池正极的活性材料为为LiFePO 4。负极的活性材料可以选自本领域常用于锂离子电池负极活性材料中的各种材料，没有特别的限定，例如可以为金属锂、石墨类碳材料、硬碳材料、软碳材料、硅基、锡基、锑基、铝基、过渡金属化合物、硅碳材料和硅氧碳中的一种或多种；优选地，所述负极的活性材料为人造石墨、天然石墨、改性天然石墨和硅氧碳中的一种或多种。
本发明中，所述锂离子电池正极和负极的制备可以按照本领域常用于制备锂离子电池正极和负极的方法进行，没有特别的限制。例如，可以将正负极的活性材料与导电剂和粘接剂混合，并将混合物分散于有机溶剂，制得浆料，之后将所得浆料涂覆于集流体上并进行干燥和延压等处理。所用导电剂、粘接剂、有机溶剂和集流体等均可采用本领域常用的材料和物质，此处不再赘述。
根据本发明，优选地，所述正极材料的压实密度为2-3g/cm 3。
根据本发明，所述负极材料的压实密度可以为1.3g/cm 3以上，优选地，所述负极材料的压实密度为1.3-1.8g/cm 3。
根据本发明，所述锂离子电池的电压区间可以为2-4V；优选地，所述锂离子电池的电压区间为2-3.65V。
本发明中，所述锂离子电池的注液系数为2-7g/Ah；优选地，所述锂离子电池的注液系数为3-5g/Ah。由此不仅可以保证电池具有良好的高温循环和存储性能，而且还可以减少电解液的使用，从而节约电池生产成本。
根据本发明，所述置于正极和负极之间的隔膜可以为本领域常用作隔膜的各种材料，没有特别的限定，例如，可以为聚烯烃类隔膜、聚酰胺类隔膜、聚砜类隔膜、聚磷腈类隔膜、聚醚砜类隔膜、聚醚醚酮类隔膜、聚醚酰胺类隔膜和聚丙烯腈类隔膜中的一种或多种。在本发明一个特别优选地实施方式中，所述隔膜选自聚乙烯类隔膜，且为聚乙烯微孔膜。
本发明中，所述锂离子电池的制备可以采用本领域常用的“三明治”法进行，例如，将涂覆有活性材料的正极片和负极片之间放置隔膜，然后将其整体进行卷绕，再将卷绕体压扁后放入包装袋内真空烘烤干燥，得到电芯，接着，将电解液注入电芯中，真空封装并静置之后进行化成即可。此方法为本领域的公知方法，此处不再赘述。
以下将通过实施例对本发明进行详细描述。以下实施例中，如无特别说明，所用材料均为市售品。
以下实施例和对比例中，化合物1-6均购自上海阿拉丁生化科技股份有限公司。
正极活性材料LiFePO 4购于深圳市德方纳米科技股份有限公司，型号为DY-3。
以下实施例和对比例中各性能的测试方法按照以下述测试例进行：
测试例1：高温循环性能测试
将以下实施例和对比例制备的锂离子电池置于恒温45℃的烘箱中，以1C的电流恒流充电至3.65V，再恒压充电至电流下降至0.1C，然后以1C的电流恒流放电至2.0V，如此循环2500次，记录第1次和第2500次的放电容量，按下式计算高温循环的容量保持率：
容量保持率(％)＝第2500次循环的放电容量/第1次循环的放电容量×100％。
测试例2：高温存储性能测试
将以下实施例和对比例制备的锂离子电池在常温下用1C恒流恒压充至3.65V，然后恒压充电至电流下降至0.1C，测量电池初始放电容量和初始电池体积，然后在60℃环境中存储30天后，以1C放电至2.0V，测量此时电池的保持容量和恢复容量及储存后电池体积，计算电池容量保持率、容量恢复率和体积膨胀率，计算公式如下：
容量保持率(％)＝保持容量/初始放电容量×100％；
容量恢复率(％)＝恢复容量/初始放电容量×100％；
体积膨胀率(％)＝(储存后电池体积-初始电池体积)/初始电池体积×100％。
测试例3：铁离子溶出测试
取循环2500次后的电池拆解，取出电池的负极和负极侧隔膜，将其置于HNO 3(浓度为14.5mol/L)和H 2O的混合液(按重量比为1:2混合)中溶解。待消解完全后取20g消解液分装50mL的试剂瓶中，然后通过电感耦合等离子体发射光谱仪(ICP-OES)测试铁离子溶出到负极和隔膜上的量。
实施例1
1)电解液的制备
将碳酸乙烯酯(EC)和碳酸甲乙酯(EMC)按重量比EC：EMC＝3：7进行混合，然后在所得混合物中加入六氟磷酸锂(LiPF 6)至摩尔浓度为1mol/L，再加入电解液总重量0.001重量％的化合物1(注：此处化合物1即为说明书中的化合物1，下同)和电解液总重量2重量％的VC；
2)正极片的制备
将正极活性材料LiFePO 4、导电剂导电碳黑Super-P和粘结剂聚偏二氟乙烯(PVDF)按照93:4:3的重量比均匀混合，然后将它们分散在N-甲基-2-吡咯烷酮(NMP)中，得到正极浆料；将正极浆料均匀涂布在铝箔的两面上，经烘干、压延(压实密度如表1所示)和真空干燥，并用超声波焊机焊上铝制引出线后得到正极板，极板的厚度为100±2μm；
3)负极片的制备
将负极活性材料改性天然石墨、导电剂导电碳黑Super-P以及粘结剂丁苯橡胶(SBR)和羧甲基纤维素(CMC)按照95:1:2.5:1.5的重量比混合均匀，然后将混合物分散于去离子水中，得到负极浆料；将负极浆料涂布在铜箔的两面上，经过烘干、压延(压实密度如表1所示)和真空干燥，并用超声波焊机焊上镍制引出线后得到负极板，极板的厚度为120±2μm；
4)电芯的制备
在正极板和负极板之间放置厚度为20μm的三层隔离膜(星源材质，12+2+2um陶瓷PP隔膜)，然后将正极板、负极板和隔膜组成的三明治结构进行卷绕，再将卷绕体压扁后放入铝箔包装袋，在75℃下真空烘烤48h，得到待注液的电芯；
5)电芯的注液和化成
在露点为-40℃以下的手套箱中，将步骤1)制备的电解液注入步骤4) 制备的电芯中，其中，注液系数为4g/Ah，然后按以下步骤进行首次充电的常规化成：0.05C恒流充电180min，0.1C恒流充电180min，静置24hr后整形封口，然后进一步以0.2C的电流恒流充电至3.65V，常温搁置24hr后，以0.2C的电流恒流放电至2.0V。
实施例2-18以及对比例1-8
按照实施例1的方法进行，不同的是，锂离子电池的正负极材料压实密度、电解液中添加的式(1)表示的化合物的种类与添加量、VC的添加量、以及其他添加剂的种类与添加量有所不同，具体内容如表1所示。
表1
Figure PCTCN2021131060-appb-000008
注：/表示未添加对应物质，LiPO 2F 2为二氟磷酸锂，DTD为硫酸乙烯酯，MMDS为甲烷二磺酸亚甲酯。
实施例1-18及对比例1-8制备的锂离子电池的相关性能如表2所示。
表2
Figure PCTCN2021131060-appb-000009
由以上实施例1-9以及对比例1的结果可知，采用本发明的正极活性材料LiFePO 4，在本发明限定的正极材料压实密度范围内，当锂离子电池非水电解液中含有VC和本发明提供的式(1)表示的化合物时，锂离子电池在高温下的存储和循环性能均可以得到不同程度的提升，并且可以有效抑制铁离子的溶出。
通过实施例7、实施例10-11、对比例1以及对比例5-6可以看出，在本 发明限定的正极材料压实密度下，在锂离子电池非水电解液中添加VC和式(1)表示的化合物可以显著提高锂离子电池的高温循环和存储性能。
由实施例1，2，7，9和对比例1的结果可以看出，采用本发明限定的正极活性材料，并在本发明限定的正极材料压实密度下，式(1)表示的化合物在电解液中的加入量在0.001-5重量％之间，都能够有效提高电池的高温存储和循环性能；当含量为0.5重量％时，其对电池性能的改善最优；当含量小于0.5重量％时，其在电池中的残余量不够，从而对电池性能的提升不显著；当含量大于0.5重量％时，其在极片中的残余量也增加，过量的式(1)表示的化合物会增加电池内部的副反应，从而不利于电池循环等性能的提升。
通过实施例7、实施例14-15和对比例8的结果可以看出，当正极材料压实密度在本发明限定范围内，且非水电解液中同时添加式(1)表示的化合物和VC时，将负极材料的压实密度控制在1.3-1.8g/cm 3的范围内，锂离子电池的高温循环和存储性能优异。
通过实施例7、实施例16-18、对比例1以及对比例2-4的结果可以看出，在本发明限定的正极材料压实密度下，通过在锂离子电池非水电解液中添加式(1)表示的化合物，并在锂离子电池非水电解液中添加LiPO 2F 2、DTD和MMDS等添加剂，可以进一步改善锂离子电池的高温循环和存储性能，但在非水电解液中不添加式(1)表示的化合物时，即使添加其他添加剂，也无法显著提高锂离子电池的高温循环和存储性能。
由对比例7和实施例7的结果可以看出，采用本发明限定的正极活性材料，并在本发明限定的正极材料压实密度下，只加入式(1)表示的化合物，不加入VC时，无法显著提高锂离子电池的高温循环和存储性能。
图1是本发明实施例7制备的锂离子电池在45℃下循环2500次的负极SEM图，图2是本发明对比例1制备的锂离子电池在45℃下循环2500次的 负极SEM图。由图1和图2可知，与对比例1相比，即只在电解液中添加2重量％的VC时，循环2500周后负极片上存在着明显的锂枝晶(图2圈出部分)，而在实施例7中，即在2重量％的VC的基础上添加0.5重量％的式(1)表示的化合物时，循环2500周后的负极上几乎没有锂枝晶存在，因此在锂离子电池电解液中，在本发明限定的正极活性材料和正极材料压实密度下，在添加VC的基础上，添加式(1)表示的化合物可以明显抑制锂枝晶的形成。
以上详细描述了本发明的优选实施方式，但是，本发明并不限于此。在本发明的技术构思范围内，可以对本发明的技术方案进行多种简单变型，包括各个技术特征以任何其它的合适方式进行组合，这些简单变型和组合同样应当视为本发明所公开的内容，均属于本发明的保护范围。

Claims (10)

  1. 一种锂离子电池，其特征在于，该锂离子电池包括正极、负极、置于正极与负极之间的隔膜以及非水电解液，
    所述正极的活性材料含有LiFePO 4，
    所述非水电解液含有有机溶剂、锂盐、碳酸亚乙烯酯和式(1)表示的化合物：
    Figure PCTCN2021131060-appb-100001
    式(1)中，R 1为2-20个碳原子的链状、环状和芳香基团中的一种或多种，
    其中，正极材料的压实密度为2g/cm 3以上。
  2. 根据权利要求1所述的锂离子电池，其中，式(1)中，所述R 1为3-18个碳原子的链状、环状和芳香基团中的一种或多种；
    优选地，所述R 1选自以下结构中的一种或多种，其中，*表示结合的位置：
    Figure PCTCN2021131060-appb-100002
  3. 根据权利要求1或2所述的锂离子电池，其中，所述式(1)表示的 化合物选自以下化合物中的一种或多种：
    Figure PCTCN2021131060-appb-100003
  4. 根据权利要求1-3中任意一项所述的锂离子电池，其中，所述非水电解液中，以非水电解液总重量计，式(1)表示的化合物的含量为0.001-5重量％；
    优选地，所述非水电解液中，以非水电解液总重量计，式(1)表示的 化合物的含量为0.001-3重量％。
  5. 根据权利要求1-3中任意一项所述的锂离子电池，其中，所述非水电解液中，以非水电解液总重量计，所述碳酸亚乙烯酯的含量为0.1-5重量％；
    优选地，所述非水电解液中，以非水电解液总重量计，所述碳酸亚乙烯酯的含量为0.5-3重量％。
  6. 根据权利要求1-3中任意一项所述的锂离子电池，其中，所述有机溶剂为环状碳酸酯、线状碳酸酯、羧酸酯和醚类中的一种或多种；
    优选地，所述环状碳酸酯包括碳酸亚乙烯酯、碳酸丙烯酯和碳酸乙烯酯中的一种或多种；
    优选地，所述线状碳酸酯包括碳酸二甲酯、碳酸二乙酯和碳酸甲乙酯中的一种或多种；
    优选地，所述羧酸酯包括醋酸甲酯、醋酸乙酯、丙酸甲酯、丙酸乙酯、丁酸甲酯、异丁酸甲酯、三甲基乙酸甲酯和三甲基乙酸乙酯中的一种或多种；
    优选地，所述醚类包括乙二醇二甲醚、1,3-二氧戊环和1,1,2,2-四氟乙基-2,2,3,3-四氟丙基醚中的一种或多种；
    更优选地，所述有机溶剂为碳酸乙烯酯和碳酸甲乙酯的混合物。
  7. 根据权利要求1-3中任意一项所述的锂离子电池，其中，所述锂盐为LiPF 6、LiBF 4、LiBOB、LiDFOB、LiPO 2F 2、LiSbF 6、LiAsF 6、LiN(SO 2CF 3) 2、LiN(SO 2C 2F 5) 2、LiC(SO 2CF 3) 3和LiFSI中的一种或多种；
    优选地，所述锂盐为LiPF 6、LiPO 2F 2和LiFSI中的一种或多种；
    优选地，所述非水电解液中，所述锂盐的含量为0.1-2mol/L；
    更优选地，所述非水电解液中，所述锂盐的含量为0.8-1.5mol/L。
  8. 根据权利要求1-3中任意一项所述的锂离子电池，其中，所述非水电解液中，进一步含有其他添加剂，所述其他添加剂为1,3-丙烷磺内酯、1,4-丁烷磺内酯、甲烷二磺酸亚甲酯、氟代碳酸乙烯酯、1,3-丙磺内酯、硫酸乙烯酯、甲基二磺酸亚甲酯、二氟磷酸锂、二氟草酸硼酸锂、三(三甲基硅烷)磷酸酯、丙烯磺酸内酯、氟苯和乙烯基碳酸乙烯酯中的一种或多种；
    优选地，所述其他添加剂为二氟磷酸锂、硫酸乙烯酯和甲烷二磺酸亚甲酯中的一种或多种；
    优选地，所述非水电解液中，以非水电解液总重量计，所述其他添加剂的含量为0.1-5重量％；
    更优选地，所述非水电解液中，以非水电解液总重量计，所述其他添加剂的含量为0.1-3重量％；
  9. 根据权利要求1-3中任意一项所述的锂离子电池，其中，所述正极材料的压实密度为2-3g/cm 3；
    优选地，负极材料的压实密度为1.3g/cm 3以上；
    更优选地，负极材料的压实密度为1.3-1.8g/cm 3。
  10. 根据权利要求1-3中任意一项所述的锂离子电池，其中，所述锂离子电池的注液系数为2-7g/Ah；
    优选地，所述锂离子电池的注液系数为3-5g/Ah；
    优选地，所述锂离子电池的电压区间为2-4V；
    更优选地，所述锂离子电池的电压区间为2-3.65V。
PCT/CN2021/131060 2020-11-30 2021-11-17 锂离子电池 WO2022111346A1 (zh)

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