Lithium ion battery

Abstract

In order to solve the problem that a nitrile additive in an existing lithium ion battery is difficult to consider high-temperature circulation, high-temperature storage and low-temperature performance of the battery, the invention provides a lithium ion battery, the lithium ion battery comprises a positive plate, a negative plate, a diaphragm and a non-aqueous electrolyte, the positive plate comprises a positive active material, and the positive active material comprises LiCoO2; the non-aqueous electrolyte comprises a nitrile compound and a lithium salt; the lithium ion battery meets the following conditions: 0.15 < = a / (b * c) < = 1, 2% < = a < = 6%, 0.5 mol / L < = b < = 3.5 mol / L, and 6eV < = c < = 10eV; wherein a is the mass percentage content of the nitrile compound in the non-aqueous electrolyte, and the unit is%; b is the molar concentration of Li < + > in the non-aqueous electrolyte, and the unit is mol / L; c is the distance between a main peak and a satellite peak in a 2p orbit XPS map of Co after formation of the positive plate, and the unit is eV.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and particularly relates to a lithium-ion battery. Background Art

[0002] Lithium-ion batteries are a new generation of rechargeable batteries following traditional storage batteries such as nickel-metal hydride batteries. They have the advantages of high working voltage, large energy density, small self-discharge, long cycle life, and wide working temperature range, and are widely used in portable 3C electronic devices such as mobile phones and laptop computers. In recent years, with the continuous improvement of the cruising range of new energy vehicles and the continuous development of the requirement for thin and light 3C digital products, the battery industry increasingly demands high energy density of lithium-ion batteries. Increasing the charging cut-off voltage of lithium-ion batteries is one of the important ways to improve the battery energy density. Because as the charging cut-off voltage increases, the cathode material can achieve a higher specific capacity, and the discharge platform is significantly improved. The combined effect of these two aspects has an immediate effect on the improvement of energy density. However, as the battery voltage gradually increases, the cathode material enters a higher de-lithiated state, the material structure stability deteriorates, and the surface oxidation also increases significantly. The instability of the material structure and its high oxidation are particularly obvious at the electrode / electrolyte interface, specifically manifested as: the battery generates gas, the internal resistance increases rapidly, and the capacity drops sharply. Therefore, high-voltage batteries require electrolytes with better high-voltage resistance.

[0003] Nitrile additives are one of the most representative additives in high-voltage lithium cobalt oxide electrolytes. With the development of high-energy density lithium cobalt oxide, the cut-off voltage gradually increases in applications, and the types and contents of nitrile additives in the adapted electrolyte formulations gradually become rich. Nitrile additives are essential in high-voltage LCO (lithium cobalt oxide) electrolytes. At voltages of 4.45V and above, usually 3 to 4 types of nitriles are used in combination; however, the increase in the dosage of nitrile additives greatly increases the electrolyte viscosity and the battery internal resistance, making it difficult to balance the high-temperature cycle, high-temperature storage, and low-temperature performance of the battery. As the charging cut-off voltage increases, the types and dosages of nitrile additives in the electrolyte gradually increase. Although nitrile additives have the effect of inhibiting the dissolution of cathode Co and improving the high-temperature cycle and high-temperature storage of the battery at high voltages, some nitrile additives have a deteriorating effect on the graphite anode. Simply increasing the dosage of nitrile additives cannot fully meet the battery performance requirements at higher voltages, and the use of nitrile additives significantly deteriorates the battery internal resistance and the low-temperature performance of the battery. Summary of the Invention

[0004] Aiming at the problem that nitrile additives in existing lithium-ion batteries are difficult to balance the high-temperature cycle, high-temperature storage, and low-temperature performance of the battery, the present invention provides a lithium-ion battery.

[0005] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0006] The present invention provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, and a non-aqueous electrolyte. The positive electrode sheet includes positive electrode active materials, and the positive electrode active materials include LiCoO2; the non-aqueous electrolyte includes a nitrile compound and a lithium salt;

[0007] The lithium-ion battery satisfies the following conditions:

[0008] 0.15 ≤ a / (b*c) ≤ 1, 2% ≤ a ≤ 6%, 0.5 mol / L ≤ b ≤ 3.5 mol / L, 6 eV ≤ c ≤ 10 eV;

[0009] Wherein, a is the mass percentage content of the nitrile compound in the non-aqueous electrolyte, with the unit of %;

[0010] b is the molar concentration of Li + in the non-aqueous electrolyte, with the unit of mol / L;

[0011] c is the spacing between the main peak and the satellite peak in the XPS spectrum of the 2p orbital of Co after the formation of the positive electrode sheet, with the unit of eV.

[0012] Optionally, the lithium-ion battery satisfies the following conditions: 0.3 ≤ a / (b*c) ≤ 0.8.

[0013] Optionally, the mass percentage content of the nitrile compound in the non-aqueous electrolyte is 3% - 5%.

[0014] Optionally, the molar concentration of Li + in the non-aqueous electrolyte is 0.9 mol / L - 1.8 mol / L.

[0015] Optionally, the nitrile compound includes one or more of dinitrile compounds and polynitrile compounds.

[0016] Optionally, the dinitrile compound includes one or more of succinonitrile, glutarodinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, and sebaconitrile; the polynitrile compound includes one or more of Compounds 1 - 15,

[0017]

[0018] Optionally, the non-aqueous electrolyte further includes a solvent, and the solvent includes one or more of cyclic carbonates, linear carbonates, carboxylic acid esters, and ether compounds.

[0019] Optionally, the lithium salt includes one or more of LiPF6, LiPO2F2, LiBF4, LiBOB, LiClO4, LiCF3SO3, LiDFOB, LiN(SO2CF3)2, and LiN(SO2F)2.

[0020] Optionally, the non-aqueous electrolyte further includes an additive, and the additive includes one or more of fluoroethylene carbonate, 1,3-propane sultone, vinylene carbonate, and ethylene sulfate.

[0021] Optionally, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the additive is 0.01% to 30%.

[0022] In the present invention, the dosage of the nitrile compound, the Li + molar concentration, and the cathode material are defined. When the three satisfy a specific relationship, the high-temperature cycle and high-temperature storage performance of the lithium cobalt oxide graphite battery under high voltage can be well improved, and the low-temperature performance can be taken into account. When the content of the nitrile compound is less than 2%, the cathode protection is insufficient, the cathode structure is unstable under high voltage, the dissolution of Co ions in the cathode is aggravated, the catalytic oxidation and decomposition of the electrolyte are caused, and the high-temperature cycle and storage performance are deteriorated. When the content of the nitrile compound is higher than 6%, the high content of the nitrile compound deteriorates the anode impedance and the battery performance decreases. When the lithium ion concentration is higher than 3.5 mol / L, the kinetic performance of the electrolyte drops significantly, the viscosity of the electrolyte increases, thereby significantly deteriorating the low temperature. There is no obvious deterioration in the short-term high-temperature cycle capacity retention, but the cycle impedance increases significantly, and at the same time, the high-temperature storage impedance growth is also deteriorated. When the lithium salt concentration is lower than 0.5 mol / L, the stability of SEI film formation and repair cannot be guaranteed during the battery cycle, and the battery capacity retention, the anode, and the gas generation increase rapidly during high-temperature cycle and high-temperature storage, resulting in thickness growth. When the spacing between the main peak and the satellite peak in the XPS spectrum of the 2p orbit of Co after the cathode sheet is formed exceeds 10 eV, the surface and bulk charges of the cathode are unbalanced, the cathode structure is unstable, and the battery performance deteriorates. Description of the Drawings

[0023] Figure 1 is the XPS spectrum of the 2p orbit of Co after the cathode sheet is formed provided in Example 4, Comparative Example 2, and Comparative Example 7 of the present invention. Detailed Description of the Invention

[0024] In order to make the technical problems, technical solutions, and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] An embodiment of the present invention provides a lithium ion battery, including a cathode sheet, an anode sheet, a separator, and a non-aqueous electrolyte. The cathode sheet includes a cathode active material, and the cathode active material includes LiCoO2; the non-aqueous electrolyte includes a nitrile compound and a lithium salt;

[0026] The lithium ion battery satisfies the following conditions:

[0027] 0.15 ≤ a / (b * c) ≤ 1, 2% ≤ a ≤ 6%, 0.5 mol / L ≤ b ≤ 3.5 mol / L, 6 eV ≤ c ≤ 10 eV;

[0028] Wherein, a is the mass percentage content of the nitrile compound in the non-aqueous electrolyte, with the unit of %;

[0029] b is the molar concentration of Li + in the non-aqueous electrolyte, with the unit of mol / L;

[0030] c is the spacing between the main peak and the satellite peak in the XPS spectrum of the 2p orbital of Co after the positive electrode sheet is formed, with the unit of eV.

[0031] In the present invention, the dosage of the nitrile compound, the molar concentration of Li + and the positive electrode material are limited. When the three satisfy a specific relationship, the high-temperature cycle and high-temperature storage performance of the lithium cobalt oxide graphite battery under high voltage can be well improved, and the low-temperature performance can be taken into account. When the content of the nitrile compound is less than 2%, the positive electrode protection is insufficient, the positive electrode structure is unstable under high voltage, the dissolution of Co ions in the positive electrode is aggravated, the catalytic oxidation and decomposition of the electrolyte are caused, and the high-temperature cycle and storage performance are deteriorated. When the content of the nitrile compound is higher than 6%, the high content of the nitrile compound deteriorates the negative electrode impedance and the battery performance decreases. When the lithium ion concentration is higher than 3.5 mol / L, the kinetic performance of the electrolyte drops significantly, the electrolyte viscosity increases, thus significantly deteriorating the low temperature. There is no obvious deterioration in the short-term high-temperature cycle capacity retention, but the cycle impedance increases significantly, and at the same time, the high-temperature storage impedance growth is also deteriorated. When the lithium salt concentration is lower than 0.5 mol / L, the stability of SEI film formation and repair cannot be guaranteed during the battery cycling process, and the battery capacity retention, the negative electrode, and the gas production increase, resulting in thickness growth during high-temperature cycling and high-temperature storage. When the spacing between the main peak and the satellite peak in the XPS spectrum of the 2p orbital of Co after the positive electrode sheet is formed exceeds 10 eV, the surface and bulk charges of the positive electrode are unbalanced, the positive electrode structure is unstable, and the battery performance is deteriorated.

[0032] Specifically, the content of the nitrile compound added to the non-aqueous electrolyte is 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, 4.2%, 4.4%, 4.8%, 5.0%, 5.2%, 5.4%, 5.6%, 5.8% or 6.0%.

[0033] The molar concentration of Li + in the non-aqueous electrolyte is 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L or 3.5 mol / L.

[0034] The spacing between the main peak and the satellite peak in the XPS spectrum of the 2p orbital of Co after the positive electrode sheet is formed is 6 eV, 7 eV, 8 eV, 9 eV or 10 eV

[0035] In a preferred embodiment, the lithium ion battery satisfies the following condition: 0.3 ≤ a / (b*c) ≤ 0.8, which can improve the high temperature cycle and high temperature storage performance of the lithium cobalt oxide graphite battery at 4.48 V to 5.2 V and take into account the low temperature performance.

[0036] In a preferred embodiment, the mass percentage content of the nitrile compound in the non-aqueous electrolyte is 3% - 5%. By controlling the content of the nitrile compound within this range, it is beneficial to improve the stability of the positive electrode structure at high voltage and improve the high temperature cycle and storage performance of the lithium ion battery.

[0037] In a preferred embodiment, Li in the non-aqueous electrolyte + The molar concentration is 0.9 mol / L - 1.8 mol / L. By controlling the molar concentration of lithium ions within this range, the kinetic performance of the electrolyte is improved, thereby improving the high temperature cycle retention performance and storage performance.

[0038] In some embodiments, the nitrile compound includes one or more of a dinitrile compound and a polynitrile compound. Specifically, the polynitrile compound is a compound containing at least three cyano groups.

[0039] In some embodiments, the dinitrile compound includes one or more of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile and sebaconitrile. The polynitrile compound includes one or more of Compounds 1 - 15,

[0040]

[0041] It should be noted that the above are only the preferred compounds of the present invention and do not represent a limitation to the present invention.

[0042] In some embodiments, the non-aqueous electrolyte further includes a solvent, and the solvent includes one or more of a cyclic carbonate, a linear carbonate, a carboxylic acid ester and an ether compound. The ether compound includes a cyclic ether or a chain ether. The cyclic ether may specifically but not limitedly be at least one of 1,3 - dioxolane (DOL), 1,4 - dioxane (DX), crown ether, tetrahydrofuran (THF), 2 - methyltetrahydrofuran (2 - CH3 - THF), 2 - trifluoromethyltetrahydrofuran (2 - CF3 - THF); The chain ether may specifically but not limitedly be dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether.

[0043] The cyclic carbonate can specifically be, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); the linear carbonate can specifically be, but is not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). There is no special limitation on the content of the cyclic carbonate, and it can be arbitrary within the range that does not significantly damage the effect of the lithium-ion battery of the present invention. However, when using only one kind, the lower limit of its content is usually 3% or more, preferably 5% or more, by volume, relative to the total amount of the solvents of the non-aqueous electrolyte. By setting this range, it is possible to avoid a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte, and it is easy to make the high-current discharge characteristics, the stability with respect to the negative electrode, and the cycle characteristics of the non-aqueous electrolyte battery reach a good range. In addition, the upper limit is usually 90% or less, preferably 85% or less, more preferably 80% or less, by volume. By setting this range, the oxidation / reduction resistance of the non-aqueous electrolyte can be improved, which helps to improve the stability during high-temperature storage.

[0044] There is no special limitation on the content of the linear carbonate. Relative to the total amount of the solvents of the non-aqueous electrolyte, it is usually 15% or more, preferably 20% or more, more preferably 25% or more, by volume. In addition, it is usually 90% or less, preferably 85% or less, more preferably 80% or less, by volume. By making the content of the linear carbonate within the above range, it is easy to make the viscosity of the non-aqueous electrolyte reach an appropriate range, suppress the decrease in ionic conductivity, and further help to make the output characteristics of the non-aqueous electrolyte battery reach a good range. When using two or more linear carbonates in combination, it is only necessary to make the total amount of the linear carbonates satisfy the above range.

[0045] The carboxylic acid ester solvents include cyclic carboxylic acid esters and / or chain carbonates. Examples of the cyclic carboxylic acid esters can include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of the chain carbonates can include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0046] In some embodiments, the lithium salt includes one or more of LiPF6, LiPO2F2, LiBF4, LiBOB, LiClO4, LiCF3SO3, LiDFOB, LiN(SO2CF3)2, and LiN(SO2F)2. Specifically, the lithium salt in the non-aqueous electrolyte is the transfer unit of lithium ions. The concentration of the lithium salt directly affects the transfer rate of lithium ions, and the transfer rate of lithium ions affects the potential change of the negative electrode. During the rapid charging process of the battery, it is necessary to improve the moving speed of lithium ions as much as possible to prevent the negative electrode potential from dropping too fast, resulting in the formation of lithium dendrites, which pose a safety hazard to the battery. At the same time, it can also prevent the rapid attenuation of the cycle capacity of the battery.

[0047] In some embodiments, the non-aqueous electrolyte further includes an additive, and the additive includes one or more of fluorinated ethylene carbonate, 1,3-propane sultone, vinylene carbonate, and ethylene sulfate. The additive can cooperate with nitrile compounds to form a structurally stable interfacial film at the positive and negative electrode interfaces, which helps to improve the electrical performance of the battery.

[0048] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the additive is 0.01% - 30%.

[0049] It should be noted that unless otherwise specified, generally, the addition amount of any optional substance in the additive in the non-aqueous electrolyte is 10% or less. Preferably, the addition amount is 0.1% - 5%, and more preferably, the addition amount is 0.1% - 2%. Specifically, the addition amount of any optional substance in the additive can be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, 10%.

[0050] The present invention will be further described below through examples.

[0051] Example 1

[0052] This example is used to illustrate the lithium-ion battery disclosed by the present invention, and includes the following operating steps:

[0053] Electrolyte: Ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate are mixed in a mass ratio of EC:PC:EMC = 10:15:75. Then, lithium hexafluorophosphate with a molar concentration of b M is added, a nitrile compound with a mass percentage of a% is added, and fluoroethylene carbonate with a mass percentage of 10% is added. The types and specific values of a and b are shown in Table 1.

[0054] Preparation of the positive electrode sheet

[0055] Take the positive electrode active material LiCoO2, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) described in Claim 1 in a mass ratio of 93:4:3 and mix them. Then disperse them in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to obtain the positive electrode slurry. Coat the obtained slurry evenly on both sides of the aluminum foil, and after drying, rolling, and vacuum drying, weld an aluminum lead wire with an ultrasonic welder to obtain the positive electrode sheet. The thickness of the positive electrode sheet is between 120 - 150 μm.

[0056] Preparation of the negative electrode sheet

[0057] Take the negative electrode active material artificial graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in a mass ratio of 94:1:2.5:2.5 and mix them. Then disperse them in an appropriate amount of deionized water to obtain the negative electrode slurry. Coat the slurry on both sides of the copper foil, and after drying, rolling, and vacuum drying, weld a nickel lead wire with an ultrasonic welder to obtain the negative electrode sheet. The thickness of the negative electrode sheet is between 120 - 150 μm.

[0058] Preparation of the battery cell

[0059] Place a three-layer separator with a thickness of 20 μm between the above-prepared positive electrode sheet and negative electrode sheet. Then wind the sandwich structure composed of the positive electrode sheet, negative electrode sheet, and separator, and after flattening the wound body, put it into an aluminum foil packaging bag and vacuum bake it at 75°C for 48 h to obtain the battery cell to be filled with electrolyte.

[0060] Filling the battery cell with electrolyte and formation

[0061] In a glove box with the moisture and oxygen content controlled below 10 ppm, inject the above-prepared electrolyte containing different concentration gradients of lithium salt and nitrile content into the battery cell. After vacuum packaging, let it stand in an incubator at 45°C for 48 h.

[0062] Use a thermal pressing formation machine to charge the battery at a low rate at a temperature of 75°C: 1. Charge at a current of 0.1C for 45 min. 2. Charge at a current of 0.2C for 30 min. 3. Charge at a current of 0.5C until it reaches 4.6V cutoff to complete the formation of the battery cell.

[0063] The final positive electrode active material was obtained by secondary sintering of LiCoO2 precursor Li2CO and Co3O4 doped with Mg element compounds with mass fractions of 0.2%, 0.5%, 1.0%, 1.5%, 2.0%, and 2.5% at 900 °C. The function is to occupy the Co element position through different doping amounts of Mg element, so as to achieve the purpose of changing the valence state of Co ions, electron delocalization, and improving the conductivity of the active material, thereby making the main peak and satellite peak of the Co ion 2p orbital in the XPS spectrum of the positive electrode sheet after formation show different spacings.

[0064] Examples 2 - 20

[0065] Examples 2 - 20 are used to illustrate the lithium-ion battery disclosed in the present invention, including most of the operation steps in Example 1 above. The difference is that the formulation in Table 1 is adopted.

[0066] Comparative Examples 1 - 10

[0067] The comparative examples are used to compare and illustrate the lithium-ion battery disclosed in the present invention, including most of the operation steps in Example 1. The difference is that the formulation in Table 1 is adopted.

[0068] Table 1

[0069]

[0070]

[0071]

[0072] Performance Test

[0073] I. The following performance tests were carried out on the batteries prepared in the above examples and comparative examples:

[0074] For the batteries in the above examples and comparative examples after formation, one battery from each example and comparative example was selected for disassembly. The positive electrode sheet was taken and the existence form and valence state of Co element in the positive electrode were tested by X-ray photoelectron spectrometer (XPS), and the spacing c between the main peak and satellite peak in the Co2p orbital XPS spectrum was obtained;

[0075] After the remaining batteries continued to complete the formation capacity test, cyclic charge and discharge tests were carried out at 45 °C in the voltage range of 3.0 V to 4.6 V, and the capacity retention rate and DCIR growth rate of the batteries after 200 cycles were recorded; low-temperature discharge tests were carried out at -20 °C to obtain the low-temperature discharge efficiency; storage tests were carried out at 60 °C, and the capacity retention rate and internal resistance growth rate of the batteries after 21 days of storage were tested.

[0076] The test results are shown in Table 2.

[0077] Table 2

[0078]

[0079]

[0080] From the test results of Examples 1-6, Example 7, Example 11, Comparative Example 3 and Comparative Example 4, it can be seen that when the lithium salt concentration is in the range of 1-1.5 M, the cycle capacity retention at 45 °C is improved, especially the growth of cycle impedance is significantly improved, the storage at 60 °C is improved, and the low-temperature discharge capacity performs best. When the lithium salt concentration is too high, the kinetic performance of the electrolyte drops significantly, the electrolyte viscosity increases, thus significantly deteriorating the low-temperature performance. There is no obvious deterioration in the short-term high-temperature cycle capacity retention, but the cycle impedance increases significantly, and at the same time, the high-temperature storage and impedance growth are also deteriorated. When the lithium salt concentration is too low, the stability of SEI film formation and repair cannot be guaranteed during the battery cycling process, and the battery capacity retention, the negative electrode, and the gas production increase, resulting in thickness growth during high-temperature cycling and high-temperature storage.

[0081] From the test results of Example 1, Examples 7-10, and Comparative Examples 5-7, it can be seen that when the nitrile content is in the range of 2% - 6%, there is no obvious deterioration in the cycle capacity at 45 °C and the storage capacity at 60 °C, and the low-temperature performance is slightly improved. When the nitrile content is lower than this range, the stability of the positive electrode cannot be protected. When the nitrile content exceeds this range, the battery negative electrode is deteriorated, resulting in a significant deterioration in the cycle capacity retention.

[0082] From Figure 1 Examples 1, 11-14, and Comparative Examples 8-10, it can be seen that after the formation of the battery cores of different examples and comparative examples, different spacings are presented between the main peak and the satellite peak of the Co 2p orbit of the positive electrode sheet, which affects the battery performance. When the spacing between the main peak and the satellite peak of the Co 2p orbit of the positive electrode sheet after formation is within 6 eV ≤ c ≤ 10 eV, the positive electrode structure is stable. Beyond this range, the charge imbalance between the surface and the bulk of the positive electrode occurs, the positive electrode structure is unstable, and the battery performance deteriorates.

[0083] From the test results of Example 1 and Examples 15-20, it can be seen that by changing the types of nitrile compounds and lithium salts, although the test results are affected by the different types of nitrile compounds and lithium salts added compared with Example 1, and the improvement effects on the performance are different, the overall test results still show the purpose of improvement compared with the comparative examples where the nitrile compound content and lithium salt concentration exceed the value range.

[0084] It can be seen from Example 1 and Comparative Examples 1-10 that in Comparative Examples 4-10, although the relationship 0.15 ≤ a / (b*c) ≤ 1 is satisfied, the lithium ion concentration, the content of nitrile compounds, and the spacing between the main peak and the satellite peak of the Co 2p orbital of the positive electrode sheet after formation are not within the range of this example, and the requirements for improving the cycle capacity retention, storage capacity retention, and low-temperature capacity performance cannot be met. In Comparative Examples 1 and 2, the lithium ion concentration satisfies the value range of this example, but the final relationship a / (b*c) ≤ 1 is not satisfied, indicating that a lithium salt concentration of 0.5 M combined with a nitrile compound content of 6% cannot meet the requirements for improving the cycle capacity retention, storage capacity retention, and low-temperature capacity performance. It is proved that the ranges of the lithium ion concentration and the nitrile compound content also need to be satisfied simultaneously to ensure that there is no obvious deterioration in the battery cycle, battery storage, and low-temperature performance.

[0085] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, It includes a positive electrode sheet, a negative electrode sheet, a separator, and a non-aqueous electrolyte. The positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes LiCoO2; the non-aqueous electrolyte includes a nitrile compound and a lithium salt; The lithium ion battery satisfies the following conditions: 0.15 ≤ a / (b*c) ≤ 1, 2% ≤ a ≤ 6%, 0.5 mol / L ≤ b ≤ 3.5 mol / L, 6 eV ≤ c ≤ 10 eV; Wherein, a is the mass percentage content of the nitrile compound in the non-aqueous electrolyte, and the unit is %; b is the molar concentration of Li in the non-aqueous electrolyte, with the unit of mol / L; + ​ c is the spacing between the main peak and the satellite peak in the XPS spectrum of the 2p orbital of Co after the positive electrode sheet is formed, and the unit is eV.

2. The lithium-ion battery according to claim 1, wherein The lithium ion battery satisfies the following conditions: 0.3 ≤ a / (b*c) ≤ 0.

8.

3. The lithium-ion battery according to claim 1, characterized in that, The mass percentage content of the nitrile compound in the non-aqueous electrolyte is 3% - 5%.

4. The lithium-ion battery according to claim 1, characterized in that, The Li in the non-aqueous electrolyte + has a molar concentration of 0.9 mol / L - 1.8 mol / L.

5. The lithium-ion battery according to claim 1, characterized in that, The nitrile compound includes one or more of a dinitrile compound and a polynitrile compound.

6. The lithium-ion battery according to claim 5, wherein, The dinitrile compound includes one or more of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, and sebaconitrile; the polynitrile compound includes one or more of Compounds 1 - 15, 7. The lithium-ion battery according to claim 1, characterized in that, The non-aqueous electrolyte further includes a solvent, and the solvent includes one or more of a cyclic carbonate, a linear carbonate, a carboxylic acid ester, and an ether compound.

8. The lithium-ion battery according to claim 1, characterized in that, The lithium salt includes one or more of LiPF6, LiPO2F2, LiBF4, LiBOB, LiClO4, LiCF3SO3, LiDFOB, LiN(SO2CF3)2, and LiN(SO2F)2.

9. The lithium ion battery according to claim 1, wherein, The non-aqueous electrolyte further includes an additive, and the additive includes one or more of fluoroethylene carbonate, 1,3 - propane sultone, vinylene carbonate, and ethylene sulfate.

10. The lithium-ion battery according to claim 9, wherein Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the additive is 0.01% - 30%.

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