Lithium ion electrolyte and battery

Abstract

The invention relates to a lithium ion electrolyte and a battery, and belongs to the technical field of lithium ion batteries. The lithium ion electrolyte comprises a lithium salt, an organic solvent and a first additive, wherein the organic solvent comprises a first solvent, and the first solvent is selected from carbonic ester compounds substituted by hydrogen, C1-C5 alkyl, phenyl and tolyl; the first additive is selected from hydrogen, fluorine and cyano-substituted nitrile fluorobenzene compounds; in percentage by mass, the content of the first additive in the electrolyte is b% and is smaller than or equal to blt; 5. By adopting a specific type of electrolyte solvent and additive combination, the stability of an electrolyte-positive electrode / negative electrode interface can be improved, the high-temperature performance of the LCO-Gr system lithium ion battery under high voltage is remarkably improved, and the high-temperature cycle performance, the standing cycle performance, the high-temperature storage performance and the like are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion electrolyte and a battery. Background Art

[0002] As an important energy storage technology, the performance and stability of lithium-ion batteries depend largely on the selection and performance of electrolytes. The electrolyte in lithium-ion batteries mainly undertakes the function of ion transport. It not only provides a migration channel for lithium ions between the positive and negative electrodes to ensure that the battery maintains a stable ion concentration during operation, but also generates a solid electrolyte interface (CEI membrane and SEI membrane) on the positive and negative electrodes, thereby ensuring that the battery can continuously and stably supply power. However, under high voltage systems, the dissolution of transition metal ions and the continuous oxidation of conventional carbonate solvents, the instability of the electrode / electrolyte interface, etc., lead to a rapid decline in battery cycle performance. At the same time, the large amount of gas and heat generated by the decomposition of the electrolyte will cause certain safety problems, which seriously hinders the practical application of lithium-ion batteries.

[0003] Adding film-forming additives and nitrile additives such as fluoroethylene carbonate (FEC) and succinonitrile (SN) to the electrolyte is considered to be an effective means to solve the above problems. Nitrile additives can complex the transition metal Co to form a complex to inhibit the continuous oxidative decomposition of the electrolyte; FEC additives have a high film-forming potential and can preferentially form a SEI film on the negative electrode surface without increasing impedance, which can prevent further decomposition of the electrolyte. However, under high temperature conditions, FEC is easy to react with Lewis acid (PF) in the electrolyte. 5 ) undergoes a de-F reaction, producing HF and other acids, which in turn causes the battery capacity to decay.

[0004] Therefore, there is an urgent need to develop an electrolyte that can inhibit the dissolution of transition metals and has high temperature resistance, which is suitable for high-voltage lithium cobalt oxide-graphite (LCO-Gr) system lithium-ion batteries, and improve the high-temperature cycle, static cycle, high-temperature storage and hot box performance of lithium-ion batteries under high voltage. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a lithium ion electrolyte and a battery. The electrolyte provided by the present invention can be used in lithium ion batteries to improve the stability of the electrolyte-negative electrode interface and the stability of the electrolyte-positive and negative electrode interfaces under high temperature and high voltage, and significantly improve the performance of high temperature cycling, static cycling and high temperature storage.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present invention provides a lithium ion electrolyte, comprising the following components: a lithium salt, an organic solvent, and a first additive; the organic solvent comprises a first solvent;

[0008] The first solvent is a carbonate compound, and the carbonate compound conforms to the following formula (I):

[0009] In the formula (I), R1 and R2 are each independently hydrogen, C 1 -C 5 One of alkyl, phenyl and tolyl;

[0010] The first additive is a nitrile fluorobenzene compound, and the nitrile fluorobenzene compound conforms to the following formula (II):

[0011] In the formula (II), R3, R4, R5, and R6 are each independently one of hydrogen, fluorine, and cyano;

[0012] The mass percentage of the first additive in the lithium ion electrolyte is b%, and 1≤b<5.

[0013] The invention provides an electrolyte comprising a first solvent carbonate compound (substance A) with a specific structure, a first additive nitrile fluorobenzene compound (substance B) with a specific structure, and a lithium salt.

[0014] Among them, carbonate solvents are used to improve the thermal stability of the electrolyte. Compared with the existing technology, the electrolyte used in high-voltage LCO-Gr system lithium-ion batteries has higher conductivity, film-forming potential and boiling point, and can regulate Li + The solvation structure accelerates the solvation effect and reduces the occurrence of side reactions between the electrolyte and the electrode. The carbonate solvent selected in the present invention has higher thermal stability, a boiling point of up to 200°C, is not easy to volatilize, and has a higher flash point.

[0015] The use of a nitrile fluorobenzene compound additive with a specific structure can improve the stability of the electrolyte to the positive and negative electrode interfaces. The nitrile fluorobenzene compound selected in the present invention can not only inhibit the dissolution of Co ions, but also preferentially generate a SEI layer on the negative electrode surface to protect the negative electrode surface. Its molecular formula matrix is ​​the FB solvent commonly used in electrolytes to reduce viscosity and improve kinetics, and the introduction of a cyano group (-CN) on the benzene ring molecule can not only increase the boiling point of the nitrile fluorobenzene compound, but also make it have more functions: on the one hand, the cyano functional group can form a complex with Co ions to inhibit the dissolution of Co ions and avoid the electrolyte being continuously oxidized and decomposed by the strongly oxidizing Co ions, so it has the effect of maintaining the stability of the positive electrode interface; on the other hand, the cyano functional group has an electron-withdrawing effect. Compared with fluorobenzene, the electron cloud density at the center of the benzene ring of nitrile fluorobenzene compounds is extremely low, and it can undergo a π-π conjugation reaction with graphite, adsorb on the graphite surface and form an SEI layer to protect the anode and prevent the structure from being destroyed, so it can also be used as an excellent negative electrode film-forming additive; it can also alleviate the consumption of FEC additives during the cycle and the generation of HF at high temperatures, thereby improving the stability of the electrolyte-negative electrode interface.

[0016] The first solvent can improve the conductivity, thermal stability and reaction kinetics of the electrolyte, but it is easily oxidized and decomposed by the Co ions dissolved in the LCO material under high voltage and produces gas, while the introduction of the first additive can effectively inhibit the dissolution of Co ions and avoid the destruction of the first solvent structure. Therefore, the introduction of the first solvent and the first additive can produce a synergistic effect to effectively improve the stability of the electrolyte-positive / negative electrode interface, thereby significantly improving the high temperature performance of the high-voltage LCO-Gr lithium-ion battery.

[0017] The combined use of the specific first solvent and the specific amount of the first additive proposed in the present invention can comprehensively improve the stability of the electrolyte-positive / negative electrode interface under high temperature and high voltage, and significantly improve the high temperature cycle, static cycle and high temperature storage performance of the LCO-Gr lithium-ion battery, and has a high application value.

[0018] Preferably, the mass percentage of the first solvent in the organic solvent is a%, and the contents of the first solvent and the first additive satisfy the following relationship: 1≤a / (10×b)≤5.

[0019] Preferably, the mass percentage of the first solvent in the organic solvent is a%, and a satisfies 5≤a≤50.

[0020] Preferably, the first solvent is at least one of ethylene carbonate, propylene carbonate, diphenyl carbonate, and di-m-tolyl carbonate;

[0021] And / or, the first additive is At least one of .

[0022] Further preferably, the first solvent is diphenyl carbonate, and the first additive is

[0023]

[0024] The first solvent is preferably diphenyl carbonate. Compared with general carbonate solvents, diphenyl carbonate has two benzene rings and carbonate groups at the same time, and its structure is more complex, which can show greater polarity. The greater polarity makes it easier for benzene ring ester solvents to enter the deep solvation shell of lithium ions, reducing the solvent steric hindrance of the deep solvation shell, thereby reducing the solvation barrier so that lithium ions have lower desolvation energy, promoting reaction kinetics, and thus reducing the occurrence of some side reactions. At the same time, the benzene ring carbonate structure has a higher dielectric constant, which helps to promote the dissociation of lithium salts and thus improve the ionic conductivity of the electrolyte. In addition, the benzene ring ester solvent also has a lower viscosity and excellent solubility. While improving the thermal stability of the electrolyte, it can also take into account the kinetics and wetting properties of the electrolyte, and comprehensively improve the battery performance.

[0025] The first additive is preferably Not only the -CN group is introduced, but also more F atoms are bonded: the strongly electronegative F atoms are more inclined to connect with the alkyl groups of the organic solvent through hydrogen bonds, resulting in molecular interface interactions; this interaction can weaken the organic solvent and Li + The coordination of Li + It can be smoothly inserted into the graphite layer without organic solvent co-intercalation; therefore, the electrolyte that is essentially incompatible will become completely compatible with the graphite anode, which can reduce the EC content in the electrolyte or even eliminate EC, which can significantly reduce the occurrence of gas production. In addition, more F atoms will also generate more LiF at the anode, making the anode surface more dense and uniform, further improving the stability of the graphite structure and improving battery performance.

[0026] Preferably, the components of the lithium ion electrolyte further include a second solvent and a second additive.

[0027] The mass percentage of the first solvent in the organic solvent is a%, the mass percentage of the second solvent in the organic solvent is c%, and the mass percentage of the second additive in the lithium ion electrolyte is d%, and the following relationship is satisfied: 1≤c / a≤5, 12.5 <b+d<15。

[0028] Further preferably, the second solvent is at least one of dimethyl carbonate, 2,2-difluoroethyl acetate, ethyl propionate, and propyl propionate;

[0029] And / or, the second additive is at least one of fluoroethylene carbonate, succinonitrile, adiponitrile, and 1,3,6-hexanetrinitrile.

[0030] Further preferably, the second solvent is a mixture of dimethyl carbonate (DEC), ethyl propionate (EP) and propyl propionate (PP), and the second additive is a mixture of fluoroethylene carbonate (FEC), adiponitrile (ADN) and 1,3,6-hexanetrinitrile (HTCN).

[0031] Further preferably, in the organic solvent, the mass ratio of the second solvent to the first solvent meets the following conditions: DEC:EP:PP:first solvent=(5-30):(5-30):(5-30):(5-50).

[0032] As a preferred embodiment of the present invention, in the organic solvent, the mass ratio of the second solvent to the first solvent meets the requirement of DEC:EP:PP:first solvent=25:25:25:25.

[0033] As a preferred embodiment of the present invention, the mass percentages a% and b% of the first solvent and the second solvent in the organic solvent, and the mass percentages c% and d% of the first additive and the second additive in the lithium ion electrolyte satisfy: the c / a is a range value of one or any two of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5; and the b+d is a range value of one or any two of 13, 13.5, 14, 14.5.

[0034] As a preferred embodiment of the present invention, the mass percentages a% and b% of the first solvent and the second solvent in the organic solvent, and the mass percentages c% and d% of the first additive and the second additive in the lithium ion electrolyte satisfy the following relationship: 2≤c / a≤3, 12.5 <b+d<14。

[0035] When the ratio between the components of the electrolyte meets the above relationship, the high temperature cycle performance and high temperature cycle stability of the LCO-Gr lithium-ion battery can be further improved.

[0036] Preferably, the content of lithium salt in the lithium ion electrolyte is 5-25% by mass percentage;

[0037] And / or, the lithium salt is lithium hexafluorophosphate (LiPF 6 ), at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, lithium difluorobis(oxalato)phosphate, lithium dioxalatoborate and lithium difluorooxalatoborate.

[0038] In a second aspect, the present invention provides a lithium-ion battery, comprising the above-mentioned lithium-ion electrolyte, a positive electrode sheet, a negative electrode sheet and a separator.

[0039] As a preferred embodiment of the present invention, the positive electrode sheet comprises an aluminum foil current collector and a positive electrode membrane, wherein the positive electrode membrane comprises a positive electrode active material, lithium cobalt oxide (LiCoO 2 ), a conductive agent (Super-P) and a binder polyvinylidene fluoride (PVDF); the negative electrode plate includes a copper foil current collector and an anode membrane, and the anode membrane includes a negative electrode active material graphite (Gr), a conductive agent acetylene black, a binder styrene-butadiene rubber (SBR) and a thickener sodium carboxymethyl cellulose (CMC).

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The present invention provides an electrolyte for a lithium ion battery by optimizing the solvent components and the structure and ratio of additives in the electrolyte. The electrolyte has better thermal stability, can effectively inhibit the dissolution of Co ions and form a stable SEI film: a specific first solvent can effectively improve the thermal stability of the electrolyte, regulate the solvation structure, reduce the desolvation energy barrier of lithium ions, accelerate the reaction kinetics, and reduce the side reaction between the electrolyte and the positive electrode; the -CN group in the structure of the multifunctional nitrile fluorobenzene compound of the first additive can effectively inhibit the dissolution of Co at the positive electrode and avoid the added first solvent structure being oxidized and decomposed and destroyed by the Co ions dissolved in the LCO material, while the F group can regulate the solvation structure and form a stable SEI film on the surface of the negative electrode; the electrolyte of the present invention can comprehensively and significantly improve the high temperature performance of the LCO-Gr system lithium ion battery under high voltage, and has high application value. DETAILED DESCRIPTION

[0042] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below in conjunction with specific examples. The test methods used in the following examples are conventional methods unless otherwise specified; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0043] The serial numbers, CAS numbers, names and structures of the first solvents and first additives used in the examples and comparative examples of the present invention are shown in Table 1 below.

[0044] Table 1 The first solvent and the first additive in the examples and comparative examples

[0045]

[0046]

[0047] Example 1

[0048] An embodiment of the lithium ion electrolyte and battery of the present invention, the preparation method of the lithium ion electrolyte in this embodiment is as follows:

[0049] (1) In a glove box filled with argon, a first solvent and a second solvent are mixed to obtain a mixed organic solvent; the first solvent is A1: ethylene carbonate, the second solvent is a mixture of dimethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP), and the mass ratio of DEC, EP, PP, and the first solvent A1 in the mixed organic solvent is DEC:EP:PP:first solvent A1=25:25:25:25 (i.e., the mass percentage of the first solvent A1 in the mixed organic solvent is 25%);

[0050] (2) Slowly add lithium salt LiPF to the mixed organic solvent obtained in step (1) 6 , add the first additive and the second additive after mixing evenly, and stir evenly to obtain the lithium ion electrolyte of this embodiment.

[0051] In the step (2), the added lithium salt LiPF 6 The mass percentage in the electrolyte is 15%; the first additive is B1: 2,6-difluorobenzonitrile, and the mass percentage of the first additive in the electrolyte is 1%; the second additive is a mixture of fluoroethylene carbonate (FEC), adiponitrile (ADN), and 1,3,6-hexanetrinitrile (HTCN), and the mass percentage of FEC in the electrolyte is 10%, the mass percentage of ADN in the electrolyte is 1%, and the mass percentage of HTCN in the electrolyte is 1%.

[0052] The preparation method of the lithium ion battery described in this embodiment is as follows:

[0053] S1. Preparation of positive electrode sheet

[0054] The positive electrode material (main active material LiCoO 2 , Xiatung New Energy), conductive agent Super P, and binder PVDF are mixed in N-methylpyrrolidone (NMP) solvent in a mass ratio of 97:2:1, and stirred to obtain a positive electrode slurry; the positive electrode slurry is coated on a current collector aluminum foil, dried at 85°C, cold pressed, and then trimmed and striped, dried at 85°C under vacuum for 6 hours, and the pole ears are welded to obtain the lithium battery positive electrode sheet required in Example 1;

[0055] S2. Preparation of negative electrode sheet

[0056] The negative electrode active material artificial graphite (active material graphite, Shenzhen BTR), conductive agent acetylene black, binder SBR, thickener CMC are fully stirred and mixed in a deionized water solvent system at a mass ratio of 96:1:1.5:1.5, coated on the negative electrode current collector Cu foil, dried, cold pressed, and slit to obtain the negative electrode sheet;

[0057] S3. Preparation of soft-pack lithium battery

[0058] A polyethylene (PE) porous polymer film (Shenzhen Xingyuan) is used as an isolation membrane. The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets, and wound to obtain a bare battery cell; the battery cell is designed to have a capacity of 5.0Ah and a voltage range of 3.0-4.55V. The bare battery cell is placed in an aluminum-plastic film outer package for packaging, and then the battery cell is placed in a vacuum oven at 85°C and baked for 48 hours. The electrolyte is injected into the dried battery with an injection coefficient of 1.5g / Ah, and the battery is packaged, left to stand, formed, shaped, and divided into different volumes, and then sealed again with a liquid retention coefficient of 1.3g / Ah to obtain the lithium-ion battery.

[0059] Examples 2 to 15 and Comparative Examples 1 to 10

[0060] The difference between Examples 2 to 15 and Comparative Examples 1 to 10 and Example 1 is that different lithium ion electrolyte components are used, as shown in Table 2. The ratio of each component in the mixed organic solvent is a mass ratio, and the content of the first solvent is a%, and the content of the second solvent is c% in terms of the mass percentage of the mixed organic solvent; the content of the lithium salt, the first additive, and the second additive is b% and d% in terms of the mass percentage of the electrolyte.

[0061] Table 2 Components of lithium ion battery electrolyte in the embodiments and comparative examples

[0062]

[0063]

[0064]

[0065]

[0066] Effect example

[0067] In order to explore the performance of the lithium ion electrolyte and battery provided by the present invention, the lithium ion batteries of Examples 1-15 and Comparative Examples 1-10 were subjected to the following relevant performance tests:

[0068] (1) Normal temperature cycle performance test: The divided battery is charged to 4.55V at 1.2C constant current and constant voltage in a 25°C environment, with a cut-off current of 0.05C, and then discharged to 3.0V at 0.5C constant current. This cycle is repeated 400 times. After the cycle, the capacity retention rate and thickness expansion rate at the 400th week are calculated. The calculation formula is as follows:

[0069] 400th cycle capacity retention rate (%) = (400th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0070] Thickness growth rate at the 400th cycle = (thickness at full charge at the 400th cycle / thickness at full charge at the first cycle) × 100%

[0071] (2) High temperature cycle performance test: In a 45°C environment, the divided battery is charged to 4.55V at a constant current and constant voltage of 0.7C, with a cut-off current of 0.05C, and then discharged to 3.0V at a constant current of 0.5C. This cycle is repeated 300 times. After the cycle, the capacity retention rate and thickness expansion rate at the 300th week are calculated. The calculation formula is as follows:

[0072] 300th cycle capacity retention rate (%) = (300th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0073] Thickness growth rate at the 300th cycle = (thickness at full charge at the 300th cycle / thickness at full charge at the first cycle) × 100%

[0074] (3) Static cycle performance test: In a 45°C environment, the divided battery is charged to 4.55V at 0.7C constant current and constant voltage, with a cut-off current of 0.05C. It is left to stand for 24 hours in a fully charged state, and then discharged to 3.0V at 0.5C constant current. This cycle is repeated 120 times. After the cycle, the capacity retention rate and thickness expansion rate of the 120th cycle are calculated. The calculation formula is as follows:

[0075] The 120th cycle capacity retention rate (%) = (120th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0076] Thickness expansion rate at the 120th cycle = (thickness at full charge at the 120th cycle / thickness at full charge at the first cycle) × 100%

[0077] (4) 85℃ 24h high temperature storage test: The battery is placed at room temperature and charged and discharged once at 0.5C (3.0V-4.55V), and the discharge capacity C of the battery before storage is recorded. 0 Then the battery was charged to 4.55V (100% SOC) with constant current and constant voltage, and the thickness of the battery before high temperature storage was measured using a PPG battery thickness gauge (600g). 1, store the battery in a constant temperature box at 85℃ for 24h, take out the battery after storage and test the thermal thickness d of the battery after storage 2 , calculate the battery thickness expansion rate after the battery is stored at 85℃ for 24h; after the battery is cooled at room temperature for 24h, discharge the battery at 0.5C constant current to 3.0V again, and then charge it at 0.5C constant current and constant voltage to 4.55V, and record the battery discharge capacity C after storage 1 and charging capacity C 2 , calculate the capacity remaining rate and recovery rate of the battery after being stored at 85℃ for 24h. The calculation formula is as follows:

[0078] Thickness expansion ratio after storage at 85℃ for 24h = (d 2 -d 1 ) / d 1 ×100%;

[0079] After 24h storage at 85℃, the remaining capacity is C 1 / C 0 ×100%;

[0080] Capacity recovery rate after storage at 85℃ for 24h = C 2 / C 0 ×100%.

[0081] (5) Thermal shock performance test: At 25°C, discharge the battery to 3.0V at a given current of 0.2C; leave it for 5 minutes; charge it to 4.55V at a charging current of 0.2C. When the cell voltage reaches 4.55V, change to 4.55V constant voltage charging until the charging current is ≤0.05C of the cut-off current; after leaving it for 1 hour, place the cell in an oven, raise the oven temperature to 135±2°C at a rate of 5±2°C / min, and keep it for 60 minutes before stopping. The judgment standard is that the cell does not catch fire or explode.

[0082] The results of the above performance tests are shown in Table 3.

[0083] Table 3 Performance test results of lithium ion batteries in the embodiments and comparative examples

[0084]

[0085]

[0086]

[0087] A comprehensive comparison of the performance of the lithium-ion batteries in the embodiments and comparative examples shows that:

[0088] In the embodiment, the electrolyte of the present invention is adopted, a carbonate compound A is introduced as the first solvent, and a nitrile fluorobenzene compound B is introduced as the first additive, so that the thermal stability of the electrolyte and the interfacial stability of the electrolyte to the positive and negative electrodes are improved, and the role of the FEC additive in the negative electrode film formation is partially replaced, and the problem of interface instability of the high FEC electrolyte of the LCO-Gr system at high temperature is effectively alleviated. The room temperature and high temperature cycle performance, static cycle performance, capacity retention rate, and thermal shock pass rate under a high voltage of 4.55V are significantly better than those of the battery prepared by the electrolyte without using the first solvent and the first additive in Comparative Example 1, and the electrolyte without using the first solvent or the first additive in Comparative Examples 2-8, and the thickness expansion rate is lower and the stability is high.

[0089] By comparing Examples 1-12, it can be seen that, under the premise that other conditions remain unchanged, the first solvent diphenyl carbonate (A3) and the first additive tetrafluoroterephthalonitrile (B3) are preferably selected, which is more helpful to improve the thermal stability of the electrolyte while taking into account the dynamics and wetting properties of the electrolyte, and further improve the stability of the graphite structure in the battery, thereby comprehensively improving the battery performance. The room temperature and high temperature cycle retention rates are both high, at more than 92.8%, the static cycle retention rate is more than 75%, and the thickness expansion rate is the lowest.

[0090] Comparative Examples 11, 13 and Comparative Examples 9 and 10 show that the amount of the first additive in the lithium ion electrolyte also has a certain effect on the overall performance of the battery. Excessive dosage will lead to enhanced intermolecular association of the solvent, enhanced electrolyte viscosity, and reduced lithium ion mobility; when the dosage is insufficient, the cobalt ions dissolved from the positive electrode cannot be effectively complexed, resulting in oxidative decomposition of the electrolyte under high temperature and high pressure, thereby causing capacity decay. Therefore, when the dosage is too high or too low, the high temperature cycle, static cycle and high temperature storage performance of the battery may be reduced. Comparative Example 11 and Examples 14 and 15 show that the ratio relationship between the first solvent and the second solvent in the lithium ion electrolyte of the present invention, the content relationship between the first additive (A) and the first solvent (B), and the total proportion of the additives have a certain effect on the room temperature and high temperature cycle performance of the lithium battery, among which the thickness expansion rate of the high temperature cycle is more significantly affected. Under the relationship of the appropriate first solvent content a%, the first additive content b%, the second solvent content c%, and the second additive content d% in Example 11, the optimal high temperature cycle stability of the battery can be comprehensively achieved.

[0091] In summary, the thickness growth and cycle decay of the high-voltage LCO-Gr system lithium-ion battery using conventional electrolytes during the cycle are relatively fast, and the high-temperature cycle and static cycle performance are relatively poor. However, the high-temperature performance of the lithium battery using the lithium-ion electrolyte of the present invention is significantly improved, making the 4.55V high-voltage LiCoO 2 -Gr system lithium batteries have improved high temperature electrochemical performance and have high practical value.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A lithium ion electrolyte, characterized in that: The method comprises the following components: a lithium salt, an organic solvent, and a first additive; the organic solvent comprises a first solvent; The first solvent is a carbonate compound, and the carbonate compound conforms to the following formula (I): In the formula (I), R1 and R2 are each independently one of hydrogen, C1-C5 alkyl, phenyl, and tolyl; The first additive is a nitrile fluorobenzene compound, and the nitrile fluorobenzene compound conforms to the following formula (II): In the formula (II), R3, R4, R5, and R6 are each independently one of hydrogen, fluorine, and cyano; The mass percentage of the first additive in the lithium ion electrolyte is b%, and 1≤b<5.

2. The lithium ion electrolyte according to claim 1, characterized in that The mass percentage of the first solvent in the organic solvent is a%, and the contents of the first solvent and the first additive satisfy the following relationship: 1≤a / (10×b)≤5.

3. The lithium ion electrolyte according to claim 1, characterized in that The mass percentage of the first solvent in the organic solvent is a%, and a satisfies 5≤a≤50.

4. The lithium ion electrolyte according to claim 1, characterized in that The first solvent is at least one of ethylene carbonate, propylene carbonate, diphenyl carbonate, and di-m-tolyl carbonate; And / or, the first additive is At least one of .

5. The lithium ion electrolyte according to claim 4, characterized in that The first solvent is diphenyl carbonate, and the first additive is 6. The lithium ion electrolyte according to claim 1, characterized in that The components of the lithium ion electrolyte also include a second solvent and a second additive. The mass percentage of the first solvent in the organic solvent is a%, the mass percentage of the second solvent in the organic solvent is c%, and the mass percentage of the second additive in the lithium ion electrolyte is d%, and the following relationship is satisfied: 1≤c / a≤5, 12.5 <b+d<15。 7. The lithium ion electrolyte according to claim 6, characterized in that The second solvent is at least one of dimethyl carbonate, 2,2-difluoroethyl acetate, ethyl propionate, and propyl propionate; And / or, the second additive is at least one of fluoroethylene carbonate, succinonitrile, adiponitrile, and 1,3,6-hexanetrinitrile.

8. The lithium ion electrolyte according to claim 7, characterized in that The second solvent is a mixture of dimethyl carbonate, ethyl propionate and propyl propionate, and the second additive is a mixture of fluoroethylene carbonate, adiponitrile and 1,3,6-hexanetrinitrile.

9. The lithium ion electrolyte according to claim 1, characterized in that The content of lithium salt in the lithium ion electrolyte is 5-25% by mass percentage; And / or, the lithium salt is at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, lithium difluorobis(oxalato)phosphate, lithium dioxalatoborate and lithium difluorooxalatoborate.

10. A lithium ion battery, characterized in that: It comprises the lithium ion electrolyte, the positive electrode sheet, the negative electrode sheet and the isolation membrane as described in any one of claims 1 to 9.

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