阅读说明：本技术 一种锂离子电池 (Lithium ion battery ) 是由 梁成都 李志强 韩昌隆 于 2019-07-30 设计创作，主要内容包括：本发明涉及电化学领域,特别是涉及一种锂离子电池。本发明一方面提供一种锂离子电池,包括正极极片、负极极片、隔离膜和电解液,所述负极极片包括含有负极活性物质的负极活性物质层,所述电解液包括电解质锂盐,所述电解质锂盐包括第一锂盐和第二锂盐；所述第一锂盐选自含氟磺酰亚胺锂盐,所述第一锂盐与所述负极极片满足关系式(1)。本发明采用含氟磺酰亚胺锂盐作为第一锂盐的电解液,可以有效抑制电池的阻抗增加过快或浓度极化过大,能够充分发挥含氟磺酰亚胺锂盐的高温优势和高电导率优势,形成的电池浮充物理电阻增加率较低,避免在循环中后期产生析锂等安全问题,最终达到安全性能高、循环寿命长、高温存储好的优异性能。(The invention relates to the field of electrochemistry, in particular to a lithium ion battery. The invention provides a lithium ion battery, which comprises a positive pole piece, a negative pole piece, a separation film and electrolyte, wherein the negative pole piece comprises a negative active material layer containing a negative active material, the electrolyte comprises electrolyte lithium salt, and the electrolyte lithium salt comprises a first lithium salt and a second lithium salt; the first lithium salt is selected from fluorine-containing sulfimide lithium salt, and the first lithium salt and the negative electrode sheet satisfy the relation (1). According to the invention, the fluorine-containing sulfimide lithium salt is used as the electrolyte of the first lithium salt, so that the excessively fast increase of the impedance or the excessively large concentration polarization of the battery can be effectively inhibited, the high-temperature advantage and the high conductivity advantage of the fluorine-containing sulfimide lithium salt can be fully exerted, the increase rate of the floating charge physical resistance of the formed battery is low, the safety problems of lithium precipitation and the like generated in the middle and later periods of circulation are avoided, and finally the excellent performances of high safety performance, long circulation life and good high-temperature storage are achieved.)

1. The utility model provides a lithium ion battery, includes positive pole piece, negative pole piece, barrier film and electrolyte, negative pole piece is including the negative pole active material layer that contains the negative pole active material, electrolyte includes electrolyte lithium salt, its characterized in that:

the electrolyte lithium salt comprises a first lithium salt and a second lithium salt, wherein the molar ratio of the first lithium salt to the second lithium salt is 1: 1-20: 1; the first lithium salt is selected from fluorine-containing lithium sulfonimide,

the first lithium salt and the negative electrode sheet satisfy the relation (1):

the unit is g/cm³；

Wherein M is_EThe total mass of the electrolyte in the lithium ion battery is g;

C_Iis the mass percentage of the first lithium salt relative to the electrolyte, in%;

M_Athe total mass of the negative active material layer in the lithium ion battery is g;

PD_Ais a compacted density of the anode active material layer in g/cm³；

P_AIs the porosity of the anode active material layer in%.

2. The lithium ion battery of claim 1, wherein the first lithium salt and the negative electrode tab satisfy relation (1);

the unit is g/cm³。

3. The lithium ion battery of claim 1 or 2, wherein the lithium salt of the fluorosulfonyl imide is a lithium salt having a chemical formula shown in formula I:

wherein R is₁And R₂Each independently selected from a fluorine atom, or an optionally fluorine-substituted hydrocarbon group having 1 to 8 carbon atoms, and R₁And R₂At least one of which comprises fluorine; preferably, R₁And R₂Can be respectively and independently selected from-C_aH_bF_cor-CF₂CF₂(OCF₂CF₂)_dF, wherein a is 0, 1, 2, 3, 4, 5, 6, 7, or 8, b and c are integers, and b + c is 2a +1, and d is 1, 2, or 3; more preferably, a is 0, 1, 2, 3 or 4; optionally, R₁And R₂May be independently selected from fluorine atom, -CH₃、-CHF₂、-CH₂F、-CF₃、-C₂F₅、-C₃F₇、-C₄F₉or-CF₂CF₂OCF₂CF₃。

4. The lithium ion battery of any one of claims 1 to 3, wherein the first lithium salt is selected from one or more of lithium bis-fluorosulfonylimide, lithium fluorosulfonyl (trifluoromethylsulfonyl) imide, lithium bis (trifluoromethyl) sulfonyl imide, lithium methyltrifluoromethylsulfonyl imide, lithium trifluoromethyl (pentafluoroethyl) sulfonyl imide, lithium bis (pentafluoroethyl) sulfonyl imide, and the like; optionally, the lithium salt of the fluorine-containing sulfonyl imide comprises lithium bis (fluorosulfonyl) imide, or the lithium salt of the fluorine-containing sulfonyl imide is selected from lithium bis (fluorosulfonyl) imide.

5. The lithium-ion battery of any of claims 1 to 4, wherein the mass percentage C of the first lithium salt relative to the electrolyte solution_IMore than or equal to 4.0wt percent,preferably, C_INot less than 5.0 wt%, more preferably, C_I≥5.5wt％。

6. The lithium ion battery of any of claims 1 to 5, wherein the second lithium salt is selected from LiPF₆、LiBF₄、LiPO₂F₂、Li₃One or more combinations of POFs.

7. The lithium-ion battery of any of claims 1 to 6, wherein the molar ratio of the first lithium salt to the second lithium salt is 1.2: 1-10: 1; optionally, the molar ratio of the first lithium salt to the second lithium salt is 6: 4-9: 1.

8. the lithium ion battery of any of claims 1 to 7, wherein the total concentration of the electrolytic lithium salt in the electrolyte is from 0.5mol/L to 2.0 mol/L; optionally, the total concentration of the electrolyte lithium salt is 0.6 mol/L-1.8 mol/L, 0.7 mol/L-1.7 mol/L, or 0.8 mol/L-1.5 mol/L.

9. The lithium ion battery of any of claims 1 to 8, wherein the electrolyte comprises an organic solvent, and wherein the content of cyclic carbonate in the organic solvent is not more than 10 wt%.

10. The lithium ion battery of any of claims 1-9, further comprising a combination of one or more of fluoroethylene carbonate, lithium difluorophosphate, lithium difluorooxalato borate, and lithium difluorobis-oxalato phosphate in the electrolyte.

11. The lithium ion battery according to any one of claims 1 to 10, wherein the negative electrode active material layer has a porosity P_A10 to 50 percent; optionally, the porosity P of the anode active material layer_A15 to 37 percent.

12. As claimed in claims 1 toThe lithium ion battery according to any one of 11, wherein the negative electrode active material layer has a compacted density PD_AIs 1.5g/cm³～2.1g/cm³(ii) a Optionally, the compacted density PD of the anode active material layer_AIs 1.5g/cm³～1.65g/cm³。

13. The lithium ion battery of any of claims 1-12, wherein the negative active material comprises one or a combination of more of artificial graphite or natural graphite;

preferably, the negative electrode active material further includes mesophase micro carbon spheres (MCMB), hard carbon, soft carbon, silicon, a silicon-carbon composite, SiO, a Li-Sn alloy, a Li-Sn-O alloy, Sn, SnO₂Lithium titanate Li of spinel structure₄Ti₅O₁₂One or more of Li-Al alloy and metallic lithium.

14. The lithium ion battery of any of claims 1-13, wherein the lithium ion battery has a float charge physical resistance increase rate Δ R ≦ 60; optionally, Δ R is less than or equal to 55; delta R is less than or equal to 50; delta R is less than or equal to 30;

ΔR＝(R2-R1)/R1 (2)

wherein R1 is the physical resistance of the lithium ion battery under 1 kHz;

r2 is the physical resistance of the lithium ion battery under 1kHz after the lithium ion battery is charged to rated voltage by a constant current of 1C, charged to a current of 0.1C by a constant voltage under the rated voltage and charged for 24h by the constant voltage under the rated voltage.

15. An automobile comprising the lithium ion battery according to any one of claims 1 to 14.

16. A consumer electronic product comprising a lithium ion battery according to any one of claims 1 to 15.

Technical Field

The invention relates to the field of electrochemistry, in particular to a lithium ion battery.

Background

Since the end of the 20 th century, lithium ion batteries have been widely used in the consumer electronics field due to their advantages of high specific energy, no memory effect, long cycle life, and the like. In recent years, the global environment protection situation is becoming more severe, and the problem of shortage of petrochemical fuels is also becoming more serious, so that the lithium ion battery as a clean energy source is becoming an important power source of automobiles with the continuous maturity of materials and processes.

In a common power battery, a ternary material of lithium iron phosphate and lithium nickel cobalt manganese oxide is mostly used as a positive active material. The lithium iron phosphate has a stable structure and low activity, can provide high safety and long cycle life, but has a low platform and low specific energy, and the energy density cannot meet the increasing requirement of the endurance mileage of the electric automobile. The nickel cobalt lithium manganate ternary material combines the advantages of lithium nickelate, lithium cobaltate and lithium manganate, has obvious advantages of service life and energy density, but the ternary material has unstable structure and is alkaline, and is influenced by trace HF in electrolyte taking lithium hexafluorophosphate as main salt, so that the safety performance is difficult to guarantee, and thermal runaway is easy to occur in the thermal shock process. Compared with lithium hexafluorophosphate, the lithium bis (fluorosulfonyl) imide (LiFSI) has lower content of F element and good thermal stability, and can provide excellent battery safety, but the high-content LiFSI can easily cause poor high-voltage resistance of the battery.

Disclosure of Invention

In view of the above-mentioned drawbacks of the prior art, an object of the present invention is to provide a lithium ion battery having high voltage endurance, which solves the problems of the prior art.

In order to achieve the above and other related objects, an aspect of the present invention provides a lithium ion battery, including a positive electrode plate, a negative electrode plate, a separator, and an electrolyte, where the negative electrode plate includes a negative active material layer containing a negative active material, the electrolyte includes an electrolyte lithium salt, the electrolyte lithium salt includes a first lithium salt and a second lithium salt, and a molar ratio of the first lithium salt to the second lithium salt is 1: 1-20: 1; the first lithium salt is selected from fluorine-containing sulfimide lithium salt, and the first lithium salt and the negative electrode piece satisfy the relation (1) (g/cm)³)：

Wherein M is_EThe total mass of the electrolyte in the lithium ion battery is g;

C_Iis the mass percentage of the first lithium salt relative to the electrolyte, in%;

M_Athe total mass of the negative active material layer in the lithium ion battery is g;

PD_Ais a compacted density of the anode active material layer in g/cm³；

P_AIs the porosity of the anode active material layer in%.

In any embodiment, the first lithium salt and the negative electrode tab satisfy relation (1);

the unit is g/cm³。

In any embodiment, the lithium salt of fluorosulfonyl imide is a lithium salt having a chemical structure according to formula I:

wherein R is₁And R₂Each independently selected from a fluorine atom, or an optionally fluorine-substituted hydrocarbon group having 1 to 8 carbon atoms, and R₁And R₂At least one of which comprises fluorine; preferably, R₁And R₂Can be respectively and independently selected from-C_aH_bF_cor-CF₂CF₂(OCF₂CF₂)_dF, wherein a is 0, 1, 2, 3, 4, 5, 6, 7, or 8, b and c are integers, and b + c is 2a +1, and d is 1, 2, or 3; more preferably, a is 0, 1, 2, 3 or 4; optionally, R₁And R₂May be independently selected from fluorine atom, -CH₃、-CHF₂、-CH₂F、-CF₃、-C₂F₅、-C₃F₇、-C₄F₉or-CF₂CF₂OCF₂CF₃。

In any embodiment, the first lithium salt is selected from one or more of lithium bis (fluorosulfonyl) imide, lithium fluorosulfonyl (trifluoromethylsulfonyl) imide, lithium bis (trifluoromethyl) sulfonyl imide, lithium methyltrifluoromethylsulfonyl imide, lithium trifluoromethyl (pentafluoroethyl) sulfonyl imide, lithium bis (pentafluoroethyl) sulfonyl imide, and the like; optionally, the lithium salt of the fluorine-containing sulfonyl imide comprises lithium bis (fluorosulfonyl) imide, or the lithium salt of the fluorine-containing sulfonyl imide is selected from lithium bis (fluorosulfonyl) imide.

In any embodiment, the mass percentage C of the first lithium salt with respect to the electrolyte solution_INot less than 4.0 wt%, preferably, C_INot less than 5.0 wt%, more preferably, C_I≥5.5wt％。

In any embodiment, the second lithium salt is selected from LiPF₆、LiBF₄、LiPO₂F₂、Li₃One or more combinations of POFs.

In any embodiment, the molar ratio of the first lithium salt to the second lithium salt is 1.2: 1-10: 1; optionally, the molar ratio of the first lithium salt to the second lithium salt is 6: 4-9: 1.

in any embodiment, the total concentration of the electrolytic lithium salt in the electrolyte is 0.5mol/L to 2.0 mol/L; optionally, the total concentration of the electrolyte lithium salt is 0.6 mol/L-1.8 mol/L, 0.7 mol/L-1.7 mol/L, or 0.8 mol/L-1.5 mol/L.

In any embodiment, the electrolyte includes an organic solvent, and the content of the cyclic carbonate in the organic solvent is not more than 10 wt%.

In any embodiment, the electrolyte further comprises one or more of fluoroethylene carbonate, lithium difluorophosphate, lithium difluorooxalato borate and lithium difluorobis-oxalato phosphate.

In any embodiment, the porosity P of the anode active material layer_A10 to 50 percent; optionally, the porosity P of the anode active material layer_A15 to 37 percent.

In any embodiment, the anode active material layer has a compacted density PD_AIs 1.5g/cm³～2.1g/cm³(ii) a Optionally, the compacted density PD of the anode active material layer_AIs 1.5g/cm³～1.65g/cm³。

In any embodiment, the negative electrode active material comprises one or a combination of artificial graphite or natural graphite; preferably, the negative electrode active material further includes mesophase micro carbon spheres (MCMB), hard carbon, soft carbon, silicon, a silicon-carbon composite, SiO, a Li-Sn alloy, a Li-Sn-O alloy, Sn, SnO₂Lithium titanate Li of spinel structure₄Ti₅O₁₂One or more of Li-Al alloy and metallic lithium.

In any embodiment, the lithium ion battery has a float charge physical resistance increase rate Δ R of 60 or less; optionally, Δ R is less than or equal to 55; delta R is less than or equal to 50; delta R is less than or equal to 30;

ΔR＝(R2-R1)/R1 (2)

wherein R1 is the physical resistance of the lithium ion battery under 1 kHz;

r2 is the physical resistance of the lithium ion battery under 1kHz after the lithium ion battery is charged to rated voltage by a constant current of 1C, charged to a current of 0.1C by a constant voltage under the rated voltage and charged for 24h by the constant voltage under the rated voltage.

In a second aspect, the present invention provides an automobile comprising the lithium ion battery of the first aspect.

In a third aspect, the invention provides a consumer electronic product comprising the lithium ion battery of the first aspect of the invention.

Compared with the prior art, the invention has the beneficial effects that:

according to the invention, the fluorine-containing sulfimide lithium salt is used as the electrolyte of the first lithium salt, and the content of the fluorine-containing sulfimide lithium salt which can be contained in a single volume hole in the negative electrode plate is controlled within a certain range, so that the excessively fast impedance increase or the excessively large concentration polarization of the battery can be effectively inhibited, the high-temperature advantage and the high-conductivity advantage of the fluorine-containing sulfimide lithium salt can be fully exerted, the increase rate of the floating charge physical resistance of the formed battery is low, the safety problems of lithium precipitation and the like in the middle and later periods of circulation are avoided, and finally the excellent performances of high safety performance, long circulation life and good high-temperature storage are achieved.

Detailed Description

The lithium ion battery of the present invention is explained in detail below.

The invention provides a lithium ion battery (also called a lithium ion secondary battery) in a first aspect, which comprises a positive pole piece, a negative pole piece, a separation film and electrolyte, wherein the negative pole piece comprises a negative active material layer containing a negative active material, the electrolyte comprises electrolyte lithium salt, the electrolyte lithium salt comprises first lithium salt, the first lithium salt is selected from fluorine-containing sulfimide lithium salt, and the first lithium salt and the negative pole piece satisfy the relation (1) (g/cm)³)：

Wherein M is_EThe total mass of the electrolyte in the lithium ion battery is g; c_IIs the mass percentage of the first lithium salt relative to the electrolyte, in%; m_AIs the total mass of the negative active material layer in the lithium ion batteryThe bit is g; PD (photo diode)_AIs a compacted density of the anode active material layer in g/cm³；P_AIs the porosity of the anode active material layer in%. In the invention, in order to solve the safety risk possibly brought to the ternary material by trace HF in the electrolyte, the lithium salt with lower F element content is used as the main salt of the electrolyte, wherein the fluorine-containing sulfimide lithium salt has lower F element relative content and good thermal stability, the generated HF content is less, the gas generation problem of the anode material can be effectively inhibited, the excellent battery safety can be provided, in addition, the conductivity of the fluorine-containing sulfimide lithium salt after being prepared into the electrolyte is higher than that of a lithium hexafluorophosphate electrolyte, and the fluorine-containing sulfimide lithium salt has obvious advantages in cycle and storage life.

In the lithium ion battery provided by the invention, when the concentration of the fluorine-containing lithium sulfonyl imide in the electrolyte is too high, the viscosity of the electrolyte is increased and the fluidity is deteriorated, so that the wide application of the substance in the lithium ion battery is influenced. According to the invention, according to the microstructure characteristics of the negative electrode plate, the content of the fluorine-containing sulfimide lithium salt capable of being contained in the unit volume pore in the negative electrode active material layer is regulated and controlled within a certain range, and the fluidity of the fluorine-containing sulfimide lithium salt in the negative electrode active material layer is controlled by controlling the liquid retention amount of the negative electrode active material layer, so that the high-safety electrolyte is effectively prevented from being rapidly consumed, the impedance of the battery is prevented from being increased too fast or the concentration polarization of the battery is prevented from being too large, and the safety problems of lithium precipitation and the like in the middle and later periods of circulation are avoided. In some embodiments of the present invention, the content of the lithium salt of fluorosulfonylimide per unit volume of pores in the negative electrode active material layer may be 0.6g/cm³～6.2g/cm³、0.6g/cm³～1.0g/cm³、1.0g/cm³～1.5g/cm³、1.5g/cm³～2.0g/cm³、2.0g/cm³～2.5g/cm³、2.5g/cm³～3.0g/cm³、3.0g/cm³～3.5g/cm³、3.5g/cm³～4.0g/cm³、4.0g/cm³～4.5g/cm³、4.5g/cm³～5.0g/cm³、5.0g/cm³～5.5g/cm³、5.5g/cm³～6.0g/cm³Or 6.0g/cm³～6.2g/cm³。

In the lithium ion battery provided by the invention, the fluorine-containing lithium sulfonyl imide salt can be a lithium salt with a chemical structural formula shown as a formula I:

wherein R is₁And R₂Each independently selected from a fluorine atom, or an optionally fluorine-substituted hydrocarbon group having 1 to 8 carbon atoms, and R₁And R₂At least one of which comprises fluorine. Preferably, R₁And R₂Can be respectively and independently selected from-C_aH_bF_cor-CF₂CF₂(OCF₂CF₂)_dF, wherein a is 0, 1, 2, 3, 4, 5, 6, 7, or 8, b and c are integers, and b + c is 2a +1, and d is 1, 2, or 3. More preferably, a is 0, 1, 2, 3 or 4, e.g. R₁And R₂May be independently selected from fluorine atom, -CH₃、-CHF₂、-CH₂F、-CF₃、-C₂F₅、-C₃F₇、-C₄F₉or-CF₂CF₂OCF₂CF₃。

In some preferred embodiments of the present invention, the lithium salt of the fluorine-containing sulfonyl imide may be selected from one or more of lithium bis-fluorine sulfonyl imide (LiFSI), lithium fluoro sulfonyl (trifluoromethyl sulfonyl) imide (LiTFSI), lithium bis (trifluoromethyl) sulfonyl imide (LiTFSI), lithium methyl trifluoromethyl sulfonyl imide (tfsi), lithium trifluoromethyl (pentafluoroethyl) sulfonyl imide, lithium bis (pentafluoroethyl) sulfonyl imide, and the like, and most preferably, the lithium salt of the fluorine-containing sulfonyl imide may comprise lithium bis-fluorine sulfonyl imide, or the lithium salt of the fluorine-containing sulfonyl imide may be selected from lithium bis-fluorine sulfonyl imide.

In the lithium ion battery provided by the invention, the mass percentage C of the first lithium salt (namely, fluorine-containing sulfimide lithium salt, LiFSI) is relative to the total mass of the electrolyte_IMay be 4.0 wt% or more, preferably may be 5.0 wt% or more, more preferablyMay be 5.5 wt% or more. In the invention, the fluorine-containing lithium sulfonylimide has the structural characteristics of high conductivity at normal temperature and higher conductivity than that of the conventional lithium salt (LiPF)₆) More stable and less sensitive to water and temperature. Therefore, the lithium salt of the fluorine-containing sulfimide has high chemical stability and electrochemical stability, and can be used for improving the stability and power performance of the electrolyte. When the relative content of the fluorine-containing lithium sulfonimide in the electrolyte is within the range, the excessive increase of the viscosity of the electrolyte can be avoided, and the ion conductivity of the electrolyte can be effectively improved.

In the lithium ion battery provided by the invention, the electrolyte lithium salt can also comprise a second lithium salt. The second lithium salt may be selected from one or a combination of inorganic lithium salts, organic lithium salts, and the like. In some embodiments of the present invention, the second lithium salt may be selected from LiPF₆、LiBF₄、LiSbF₆、LiAsF₆、LiClO₄And LiB (C)₂O4)₂Etc., more preferably, the second lithium salt may be selected from LiPF₆、LiBF₄、LiPO₂F₂、Li₃POF, etc., particularly preferably, the second lithium salt may include LiPF₆Or the second lithium salt is selected from LiPF₆。

The inventor finds that when the inorganic lithium salt containing fluorine is used as the second lithium salt and is charged for the first time, partial lithium salt is decomposed to generate fluorine ions, and the fluorine ions react with the aluminum foil to generate an aluminum fluoride passivation layer, so that the aluminum foil corrosion can be inhibited. Research shows that when the content of the inorganic fluorine-containing lithium salt in the total lithium salt is more than 10mol percent (molar ratio), the corrosion of the aluminum foil can be effectively inhibited. However, when the content of the inorganic fluorine-containing lithium salt is too large as a main lithium salt, the film forming effect at the cathode is poor, and thus the gas generation at high temperature storage is deteriorated. Therefore, when the fluorine-containing lithium sulfonimide salt is used as the first lithium salt and the inorganic fluorine-containing lithium salt is used as the second lithium salt, the problems of conductivity of the electrolyte and corrosion of the aluminum foil can be solved. In some embodiments of the present invention, the molar ratio of the first lithium salt to the second lithium salt may be in a range of 1:1 to 20:1, more preferably in a range of 1.2:1 to 10:1, and even more preferably in a range of 6:4 to 9:1, for example, the molar ratio of the first lithium salt to the second lithium salt may be 2:1 to 7:3, 7:3 to 3:1, 3:1 to 4:1, 4:1 to 5:1, 5:1 to 6:1, 6:1 to 7:1, or 7:1 to 8: 1.

In some preferred embodiments of the present invention, the total concentration of the lithium salt in the electrolyte may be 0.5mol/L to 2.0mol/L, 0.5mol/L to 0.6mol/L, 0.6mol/L to 0.7mol/L, 0.7mol/L to 0.8mol/L, 0.8mol/L to 0.9mol/L, 0.9mol/L to 1.0mol/L, 1.0mol/L to 1.1mol/L, 1.1mol/L to 1.2mol/L, 1.2mol/L to 1.3mol/L, 1.3mol/L to 1.4mol/L, 1.4mol/L to 1.5mol/L, 1.5mol/L to 1.6mol/L, 1.6mol/L to 1.7mol/L, 1.7mol/L to 1.8mol/L, 1.8mol/L to 1.9mol/L, and further preferably 0.7mol/L to 1.9mol/L, 1.9mol/L to 1.2mol/L, and more preferably, 0.7mol/L to 1.7mol/L, or 0.8mol/L to 1.5 mol/L.

In the lithium ion battery provided by the invention, the electrolyte can further comprise an additive, the oxidation potential of the additive contained in the electrolyte can be suitable for forming a relatively stable passive film on the surface of the anode, and a compact protective film can be formed on the aluminum foil under the drive of the potential while the passive film is formed, so that the corrosion resistance of the aluminum foil is improved, and the safety performance and the long-term cycle performance of the lithium ion battery are improved. In some embodiments of the invention, the additive may be selected from one or more combinations of fluoroethylene carbonate, lithium difluorophosphate, lithium difluorooxalato borate, lithium difluorobis-oxalato phosphate, and the like.

In the lithium ion battery provided by the present invention, the electrolyte may include an organic solvent, which is generally used as a solvent to form a solution system of the electrolyte, and the organic solvent included in the electrolyte may be any of various organic solvents suitable for electrolytes of lithium ion batteries in the art, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), Ethyl Methyl Carbonate (EMC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), ethylene carbonate (VEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), gamma-butyrolactone (GBL), Butylene Carbonate (BC), fluoroethylene carbonate (FEC), Methyl Formate (MF), ethyl formate, Methyl Acetate (MA), Ethyl Acetate (EA), Propyl Acetate (PA), Methyl Propionate (MP), and methyl carbonate (GBL), Ethyl Propionate (EP), Propyl Propionate (PP), Methyl Butyrate (MB), Ethyl Butyrate (EB), Sulfolane (SF), dimethylsulfone (MSM), methylethylsulfone (EMS), diethylsulfone (ESE), Tetrahydrofuran (THF), propylene sulfite, and the like. In some preferred embodiments of the present invention, when the non-aqueous organic solvent includes a cyclic carbonate (cyclic carbonate), the content of the cyclic carbonate is not more than 10 wt%, and the cyclic carbonate may include five-membered ring, six-membered ring, seven-membered ring carbonate, and macrocyclic carbonate having seven or more membered rings, and may be, for example, one or a combination of ethylene carbonate (VEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), fluoroethylene carbonate (FEC), and the like. When the electrolyte contains high-concentration fluorine-containing lithium sulfonimide salt, if the organic solvent is too high, the side reaction of the electrolyte at the cathode can be increased, the gas production is obviously increased, and the problems of safety of the lithium ion battery and gas production in the circulating process are caused.

In the lithium ion battery provided by the invention, the negative electrode pole piece generally comprises a negative electrode current collector and a negative electrode active material layer positioned on the surface of the negative electrode current collector, wherein the negative electrode active material layer generally comprises a negative electrode active material. The negative active material may be various negative active materials suitable for lithium ion batteries in the art, and for example, the negative active material may include one or more selections of artificial graphite, natural graphite, and the like. Preferably, the negative active material may further include mesophase micro carbon spheres (MCMB), hard carbon, soft carbon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO₂Lithium titanate Li of spinel structure₄Ti₅O₁₂One or more of Li-Al alloy and metallic lithium. The negative electrode current collector may be a metal foil or a porous metal plate, and the like, and for example, a metal suitable for the negative electrode current collector may be a metal such as copper, nickel, titanium, iron, or an alloy thereof.

In the lithium ion battery provided by the invention, the negative electrode active material layer can also comprise a conductive agent, a binder, a thickening agent and the like. If necessary, the negative electrode plate may further include a solvent or other additives. The conductive agent, the binder and the thickener in the negative electrode active material layer can be various materials suitable for lithium ion batteries, and can be selected by those skilled in the art according to actual needs. For example, the conductive agent may be one or more of graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers, and the like; for another example, the binder may be one or more of Styrene Butadiene Rubber (SBR), polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin (water-based acrylic resin), carboxymethyl cellulose (CMC), and the like; for another example, the thickener may be carboxymethyl cellulose (CMC) or the like.

In the lithium ion battery provided by the invention, the compaction density and the porosity of the negative active material layer are generally required to be within a proper range, so that on one hand, the volume energy density of the lithium ion battery is ensured to be higher, and meanwhile, the compression deformation of the negative active material particles is lower, which is beneficial to the rapid infiltration of electrolyte in the gaps of the negative pole piece. In some preferred embodiments of the present invention, the anode active material layer has a compacted density PD_ACan be 1.5g/cm³～2.1g/cm³、1.5g/cm³～1.6g/cm³、1.6g/cm³～1.65g/cm³、1.65g/cm³～1.7g/cm³、1.7g/cm³～1.8g/cm³、1.8g/cm³～1.9g/cm³、1.9g/cm³～2.0g/cm³Or 2.0g/cm³～2.1g/cm³Preferably 1.5g/cm³～1.65g/cm³. In other preferred embodiments of the present invention, the porosity of the negative electrode tab may be 10% to 50%, 10% to 15%, 15% to 18%, 18% to 20%, 20% to 24%, 24% to 26%, 26% to 30%, 30% to 34%, 34% to 37%, 37% to 38%, 38% to 42%, 42% to 46%, or 46% to 50%, more preferably 15% to 37%.

After the lithium ion battery is fully charged, the charging process is theoretically terminated, but in practical situations, the voltage of the battery is gradually reduced due to self-discharge in the battery, and the floating charging is that the lithium ion battery is continuously charged by a small current so as to keep the full-charge state of the battery. When the lithium ion battery is subjected to floating charge continuously for a long time, the battery is in a high-charge state for a long time, the electrolyte is easy to decompose, and the corrosion rate of anions containing the fluorine sulfonyl imide salt to the anode current collector is accelerated under high voltage, so that the resistance of the lithium ion battery is increased, and the long-term cycle performance and the safety performance of the battery are reduced.

In the lithium ion battery provided by the invention, the floating charge physical resistance increase rate delta R reflects the change rate of the physical resistance of the lithium ion battery before and after floating charge, and can be specifically obtained by the following calculation method: Δ R ═ R2-R1)/R1, where R1 is the physical resistance of the lithium ion battery at 1kHz, and R2 is the physical resistance of the lithium ion battery at 1kHz after the lithium ion battery is charged at a constant current of 1C to a rated voltage, charged at a constant voltage at the rated voltage to a current of 0.1C, and charged at a constant voltage at the rated voltage for 24 hours. In a preferred embodiment of the present invention, the upper limit of the float physical resistance increase rate Δ R is not more than 55, more preferably, the upper limit of the float physical resistance increase rate Δ R is not more than 50, and most preferably, the upper limit of the float physical resistance increase rate Δ R is not more than 30.

In the lithium ion battery provided by the invention, the positive pole piece generally comprises a positive pole current collector and a positive pole active material layer positioned on the surface of the positive pole current collector, and the positive pole active material layer generally comprises a positive pole active material. The positive active material may be any of various positive active materials suitable for secondary batteries in the art, for example, the positive active material may include, but is not limited to, a lithium transition metal composite oxide, and the like, and more particularly, the lithium transition metal composite oxide may include, but is not limited to, one or more of lithium iron phosphide, lithium iron manganese phosphide, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, or a combination of these lithium transition metal oxides with other transition metals or non-transition metals added thereto, and the like. The positive electrode current collector may be a metal foil or a porous metal plate, and the like, and for example, a metal suitable for the positive electrode current collector may be a metal such as copper, aluminum, or an alloy thereof.

The lithium ion battery provided by the present invention generally further comprises a separation membrane, which may be any separation membrane material suitable for lithium ion batteries in the art, and for example, may be one or a combination of more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, natural fiber, and the like.

In the lithium ion battery provided by the invention, the positive pole piece, the isolating membrane and the negative pole piece in the lithium ion battery can be generally used for forming a battery core of the lithium ion battery, for example, the positive pole piece, the isolating membrane and the negative pole piece can be respectively made into layers, so that the positive pole piece, the isolating membrane and the negative pole piece can be cut into target sizes and then sequentially stacked, and can be further combined with electrolyte to form the lithium ion battery. The positive pole piece, the isolating membrane and the negative pole piece can directly form a single-layer laminated battery, can be further wound to a target size to form a battery core, and can be further combined with an electrolyte to form a lithium ion battery. In a preferred embodiment of the invention, however, the lithium ion battery is a single-layer laminated battery, which on the one hand is easier to handle during float charging and on the other hand is less expensive to screen. The lithium ion battery may also include various other components that may be used in a lithium ion battery, for example, suitable components may include, but are not limited to, a package casing, tabs, external electrodes, and the like.

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

It is to be understood that the processing equipment or apparatus not specifically identified in the following examples is conventional in the art.

Furthermore, it is to be understood that one or more method steps mentioned in the present invention does not exclude that other method steps may also be present before or after the combined steps or that other method steps may also be inserted between these explicitly mentioned steps, unless otherwise indicated; it is also to be understood that a combined connection between one or more devices/apparatus as referred to in the present application does not exclude that further devices/apparatus may be present before or after the combined device/apparatus or that further devices/apparatus may be interposed between two devices/apparatus explicitly referred to, unless otherwise indicated. Moreover, unless otherwise indicated, the numbering of the various method steps is merely a convenient tool for identifying the various method steps, and is not intended to limit the order in which the method steps are arranged or the scope of the invention in which the invention may be practiced, and changes or modifications in the relative relationship may be made without substantially changing the technical content.

Example 1

Preparing a positive pole piece:

LiNi as positive electrode active material_0.8Co_0.1Mn_0.1O₂Dispersing conductive carbon black SP and binder PVDF into solvent NMP, and uniformly mixing to obtain positive electrode slurry; uniformly coating the positive electrode slurry on an aluminum foil of a positive electrode current collector, wherein the coating weight of the positive electrode slurry is 0.309g/1540.25mm²Drying, cold pressing, slitting and cutting into pieces (by weight of the solvent is not included) to obtain the positive pole piece, wherein the mass ratio of the positive active material to the conductive carbon black to the PVDF as the binder is 96:2: 2.

Preparing a negative pole piece:

dispersing a negative active material, namely natural graphite, conductive carbon black SP, a thickening agent CMC and a binder SBR in solvent deionized water according to a mass ratio of 96:1:1:2, and uniformly mixing to obtain negative slurry; uniformly coating the negative electrode slurry on a copper foil of a negative electrode current collector; through drying, cold pressing, slitting and cutting, the cold pressing pressure is adjusted to 120-250 tons,the coating weight of the negative electrode slurry was 0.15g/1540.25mm²(based on the weight not including the solvent), and a particle diameter Dv50 of the negative electrode active material particle at 14 μm to give a compacted density of 1.5g/cm³And the porosity of the negative pole piece is 30 percent. Wherein the compaction density of the negative pole piece can be calculated by the formula P ═ m/v (m is the weight of the negative pole active material layer and is expressed in g, v is the volume of the negative pole active material layer and is expressed in cm³V may be the product of the area of the anode active material layer and the thickness of the anode active material layer); the porosity of the negative electrode piece can be tested using an AccuPyc II 1340 true density instrument according to the instrument instructions.

Preparing an electrolyte:

in a glove box filled with argon (water content < 10ppm, oxygen content < 1ppm), the first lithium salt LiFSI and the second lithium salt LiPF are added₆Adding the mixture into a nonaqueous organic solvent according to a certain molar ratio (the sum of the lithium salt concentration is 1M), wherein the organic solvent is ethylene carbonate and methyl ethyl carbonate, and the content of cyclic carbonate (ethylene carbonate) is 20 wt%. After the lithium salt is completely dissolved, a proper amount of other additives are added. And uniformly stirring to obtain the electrolyte with the lithium salt concentration of 1.0 mol/L.

Preparing a diaphragm:

a 16 micron polyethylene film (PE) was used as the separator.

Preparing a lithium ion battery:

and stacking the prepared positive plate, the diaphragm and the negative plate in sequence, enabling the diaphragm to be positioned between the positive plate and the negative plate to play a role in isolating the positive plate and the negative plate, and winding to obtain the bare cell. After welding the tab, placing the naked electric core in an outer package, injecting the prepared electrolyte into the dried electric core, packaging, standing, forming, shaping, testing the capacity and the like, and finishing the preparation of the lithium ion battery. The soft package lithium ion battery has the thickness of 4.0mm, the width of 60mm and the length of 140 mm. In the soft package lithium ion battery, the total mass of the negative electrode active material layer is 25g, and the total mass of the electrolyte is 14 g.

Examples 2 to 10 and comparative examples 1 to 3

Positive electrode sheet and negative electrode in examples 2 to 10 and comparative examples 1 to 3The preparation methods of the sheet, the electrolyte and the lithium ion battery are basically the same as that of the embodiment 1, the coating weight of the negative electrode slurry, the average particle size of the negative electrode active material, the preparation parameters such as cold pressing pressure and the like are changed, and the total mass M of the negative active material is adjusted_ACompacted density PD_AAnd pole piece porosity P_AThe formulations and physical properties of the examples and comparative examples are shown in Table 1.

TABLE 1

The test method comprises the following steps:

(1) cycle performance testing of lithium ion secondary batteries:

the fresh lithium ion secondary batteries prepared in the examples and the comparative examples were left at 45 ℃ for 5 minutes, and were subjected to constant current charging at a rate of 1C to 4.2V, constant voltage charging until the current became 0.05C or less, and then left at rest for 5 minutes, and were subjected to constant current discharging at a rate of 1C to 2.8V, which is a cyclic charge and discharge process, and the discharge capacity of this time was recorded as the discharge capacity of the lithium ion secondary battery at the 1 st cycle. The lithium ion secondary battery was subjected to 100-cycle charge-discharge tests according to the above method, and the discharge capacity per one cycle was recorded.

The capacity retention (%) of the lithium ion secondary battery after 100 cycles of 1C/1C at 45 ℃ ═ 100% of (discharge capacity at 100 th cycle/discharge capacity at 1 st cycle).

(2) High-temperature storage test of lithium ion secondary batteries:

fresh lithium ion secondary batteries prepared in examples and comparative examples were left to stand at 25 ℃ for 5 minutes, and were constant-current charged to 4.2V at a rate of 1C, then constant-voltage charged to a current of 0.05C or less, and then left to stand for 5 minutes, and then constant-current discharged to 2.8V at a rate of 1C, and the discharge capacity was recorded as an initial discharge capacity.

And (3) continuously standing the lithium ion secondary battery for 5 minutes, carrying out constant current charging to 4.2V at a rate of 1C, and then carrying out constant voltage charging until the current is less than or equal to 0.05C. Then the mixture was put into an oven at 60 ℃ and left for 1 month.

After the completion of the standing, the lithium ion secondary battery was taken out from the oven. And standing for 5 minutes after the material is cooled to room temperature, charging the material to 4.2V at a constant current of 1C multiplying power, then charging the material at a constant voltage until the current is less than or equal to 0.05C, standing for 5 minutes, then discharging the material to 3.0V at a constant current of 1C multiplying power, and recording the discharge capacity as the discharge capacity after storage.

The capacity retention (%) of the lithium ion secondary battery after storage at 60 ℃ for 1 month was (discharge capacity after storage/initial discharge capacity) × 100%.

(3) Thermal shock test of lithium ion secondary battery:

fresh lithium ion secondary batteries prepared in examples and comparative examples were left to stand at 25 ℃ for 5 minutes, and were constant-current charged at a rate of 1C to 4.2V and then constant-voltage charged to a current of 0.05C or less.

The lithium ion secondary battery is placed in an oven, the temperature is raised from 25 ℃ to 130 ℃ at the rate of 2 ℃ per minute, and the temperature is kept for 2 hours. During which the temperature of the cell skin is monitored.

(4) Lithium ion battery floating charge and physical resistance test:

taking a battery containing the positive pole piece to be screened, testing the physical resistance of the battery at 1kHz, and recording the physical resistance as R1; after constant current charging at 1C to 4.2V, then constant voltage charging at 4.2V to a current of 0.1C and continuing constant voltage charging at 4.2V for 24h, the physical resistance at 1kHz was tested and recorded as R2.

The float charge physical resistance increase rate Δ R of the lithium ion battery is (R2-R1)/R1.

The results of the performance tests of the examples and comparative examples are shown in table 2:

TABLE 2

The test results were analyzed as follows.

From the embodiments 1 to 10, it can be seen that the electrolyte with the fluorine-containing sulfimide lithium salt as the first lithium salt is injected into the electrolyte, and the content of the fluorine-containing sulfimide lithium salt which can be accommodated in the pores of the negative electrode piece in unit volume is regulated and controlled, so that the performance effects of high safety and excellent cycle can be finally achieved.

It can be seen from comparative examples 1 and 3 that when the electrolyte does not contain the fluorine-containing sulfimide lithium salt, or the content of the fluorine-containing sulfimide lithium salt which can be accommodated in a single volume pore in the negative electrode plate is too low, the side reaction of the lithium ion battery is aggravated under a high-temperature or high-fully-charged state, the gas production rate of the battery is increased, the heat production is increased, and the safety, high-temperature circulation and storage are further worsened.

It can be seen from comparative example 2 that, when the content of the fluorine-containing lithium sulfonimide salt contained in the pores per unit volume in the negative electrode plate is too high, the prepared electrolyte has relatively high viscosity due to relatively high density of the fluorine-containing lithium sulfonimide salt, on one hand, the lithium ion transmission effect is reduced sharply, and on the other hand, the corrosion to the positive current collector aluminum foil is accelerated, so that the polarization of the battery is greatly increased, the increase of the floating charge resistance is too high, the cycle capacity retention rate of the lithium ion battery is reduced, and the preparation of the battery with excellent cycle is not facilitated.

From examples 7 to 9, it was further found that the content of the cyclic carbonate in the organic solvent in the electrolyte is preferably not more than 10 wt%. Aiming at reducing the gas generation of the solvent on the surface of the anode. And when characteristic additives such as fluoroethylene carbonate, lithium difluorophosphate, lithium difluorooxalato borate and the like are further introduced, the corrosion resistance of the surface of the anode aluminum foil can be further improved, the film forming effect can be further improved, the increase of the float charge resistivity of the lithium ion battery can be inhibited, and the problems of circulation and gas generation can be improved.

In conclusion, the present invention effectively overcomes various disadvantages of the prior art and has high industrial utilization value.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.