Electrolyte and lithium ion battery using the same

Abstract

The application provides a lithium ion battery to which an electrolyte is applied, the electrolyte comprising a functional additive A, and a molecular structure of the functional additive A satisfies formula I; wherein R1 and R2 are each independently selected from substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, and substituted or unsubstituted aryl; when substituted, the substituents comprise at least one of alkyl, alkoxy and halogen atoms. The application of the electrolyte can improve the cycle capacity retention rate and average working voltage of the lithium ion battery under normal temperature and high temperature use environments, and improves the battery output characteristics.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery electrolyte, in particular to an electrolyte and a lithium ion battery using the same. BACKGROUND

[0002] With the continuous prosperity of computer, communication and consumer electronics industries, the lithium ion battery industry is experiencing rapid development, and this trend is particularly evident in the rise of new energy vehicles in recent years. New energy vehicles not only accelerate the evolution of power lithium ion batteries, but also put unprecedented high standards on their energy density and safety performance. Among many performance indicators, the endurance capability of electric vehicles is particularly valued by consumers, and the energy density of the battery directly determines the single driving distance of the vehicle. Therefore, how to improve the energy density of the battery under the conditions of limited space and weight has become the focus of research inside and outside the industry. Among them, improving the working voltage of the positive electrode material is considered as one of the key ways to improve the energy density of lithium ion batteries.

[0003] For example, spinel (LNMO), ternary positive electrode material, lithium cobaltate, layered lithium-rich oxide (LLO) and other positive electrode active materials containing transition metal elements have high working voltage and exhibit unique advantages in the field of lithium ion batteries, but also face some inherent technical challenges. Specifically, during the battery cycle, these positive electrode active materials will dissolve transition metal ions, and the dissolution of transition metal ions not only consumes active materials and increases the internal resistance of the battery, but also seriously damages the internal structure of the battery and accelerates the performance degradation of the battery. With the continuous increase of the voltage of lithium ion batteries, the positive electrode material will have a higher electrode potential, and the oxidation decomposition of the electrolyte at the positive electrode and the positive electrode interface reaction will be more intense, which further dissolves the transition metal ions of the positive electrode active material.

[0004] Currently, researchers mainly modify the positive electrode material to overcome these defects, such as using surface coating, designing material microstructure, element doping and other methods. However, these material modification methods have the defects of complex process and high cost. SUMMARY

[0005] The purpose of the present application is to provide an electrolyte and a lithium ion battery using the same, which can improve the cycle capacity retention rate and average working voltage of the lithium ion battery under normal and high temperature use environments, and improve the battery output characteristics.

[0006] According to one aspect of the present application, an electrolyte is provided, comprising a functional additive A, and the molecular structure of the functional additive A satisfies formula I: R1, R2are each independently selected from substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted aryl; when substituted, the substituents include at least one of alkyl, alkoxy, halogen atom.

[0007] The present scheme can improve the cycle stability and thermal stability of the battery by introducing the functional additive A meeting formula I into the electrolyte. The functional additive A contains peroxide group and sulfonyl group at the same time, and the sulfonyl group is directly connected with the peroxide group, forming a special chemical environment, so that the functional additive A can construct a layer of CEI (solid electrolyte interface) film with stable structure, compactness and good conductivity on the positive electrode surface, thereby effectively inhibiting the dissolution of transition metal ions (TMs metal ions) from the positive electrode, reducing the concentration of TMs metal ions in the electrolyte, and reducing the unintended reaction between TMs metal ions and the electrolyte. Further, it can also avoid the migration of TMs metal ions to the negative electrode surface, thereby reducing the damage of TMs metal ions to the SEI film of the negative electrode and reducing the deposition amount of TMs metal ions on the negative electrode, thereby improving the cycle stability and thermal stability of the battery. Secondly, by introducing the functional additive A into the electrolyte, the physical structure and chemical components of the CEI film can be in-situ regulated, thereby improving the lithium conductivity of the CEI film and more efficiently transporting lithium ions, reducing the polarization phenomenon of the battery during the cycle process, slowing down the capacity decay of the battery, and especially improving the cycle capacity retention rate of the battery under high voltage or high temperature. In particular, under high temperature use environment, the transition metal elements in the positive electrode material are more likely to dissolve into the electrolyte in the form of TMs ions; and the electrolyte provided by the present application also has good heat resistance, and the CEI film formed by the functional additive A still has good mechanical properties under high temperature environment, improving the high temperature cycle and high temperature storage performance of the battery and improving the capacity retention rate.

[0008] Preferably, the functional additive A includes peroxymonosulfonic acid anhydride, bis(trifluoromethanesulfonic acid) peroxide, bis(benzenesulfonic acid) peroxide, bis(p-toluenesulfonic acid) peroxide, bis(4-(trifluoromethyl)benzenesulfonic acid) peroxide.

[0009] Preferably, the molecular structure of the functional additive A meets formula II: R3-R6are each independently selected from hydrogen, alkyl, alkoxy, halogenated alkyl, halogenated alkoxy, and R3-R6are each independently selected from hydrogen, alkyl, alkoxy, halogenated alkyl, halogenated alkoxy. 12 are each independently selected from hydrogen, alkyl, alkoxy, halogenated alkyl, halogenated alkoxy, and R3-R6are each independently selected from hydrogen, alkyl, alkoxy, halogenated alkyl, halogenated alkoxy. 12The number of carbon atoms in the formula is not more than 10. Through long-term experiments and verification, it is found that when the molecular structure of the functional additive A contains a benzene ring, and the benzene ring is directly connected with the sulfonyl group to form the structure shown in formula II, the CEI film formed by the electrolyte has a dense structure for inhibiting the dissolution of transition metal ions and excellent lithium conductivity, which helps to reduce the content of negative manganese deposition, avoid the destruction of the negative SEI film by manganese ions, and further reduce the consumption of active lithium, while helping the rapid embedding and de-embedding of lithium ions in the positive and negative electrodes, thereby improving the cycle stability of the battery. In addition, by optimizing the number of carbon atoms in R3-R 12 The number of carbon atoms in the formula is not more than 10. Through long-term experiments and verification, it is found that when the molecular structure of the functional additive A contains a benzene ring, and the benzene ring is directly connected with the sulfonyl group to form the structure shown in formula II, the CEI film formed by the electrolyte has a dense structure for inhibiting the dissolution of transition metal ions and excellent lithium conductivity, which helps to reduce the content of negative manganese deposition, avoid the destruction of the negative SEI film by manganese ions, and further reduce the consumption of active lithium, while helping the rapid embedding and de-embedding of lithium ions in the positive and negative electrodes, thereby improving the cycle stability of the battery. In addition, by optimizing the number of carbon atoms in R3-R

[0010] Preferably, the functional additive A includes bis(benzenesulfonic acid) peroxide, bis(p-toluenesulfonic acid) peroxide, bis(4-(trifluoromethyl)benzenesulfonic acid) peroxide.

[0011] Preferably, the functional additive A includes bis(benzenesulfonic acid) peroxide. The electrolyte prepared by selecting bis(benzenesulfonic acid) peroxide as the functional additive A can effectively improve the cycle performance of the battery using the electrolyte at room temperature and high temperature environments.

[0012] Preferably, the content of the functional additive A is 0.3-1% based on the total mass of the electrolyte. The functional additive A in the above content range can improve the structural stability and thermal stability of the CEI film, effectively reduce the interface impedance, improve the cycle performance of the battery, delay the aging of the battery, and prolong the cycle life of the battery.

[0013] Preferably, the electrolyte further includes a sulfur-containing additive, and the sulfur-containing additive includes at least one of 1.3-propane sulfone, 1,3-propylene sulfone, and vinyl sulfate. Further, the introduction of the sulfur-containing additive into the electrolyte can promote the formation of a dense, flexible, and low-impedance CEI film on the positive electrode surface, which can form a tight structure layer without increasing the battery impedance, and improve the cycle performance and high-temperature performance of the lithium ion battery.

[0014] Preferably, the mass ratio of the sulfur-containing additive to the functional additive A is 1-3:0.3-1.

[0015] Preferably, the content of the sulfur-containing additive is 0.5-3% based on the total mass of the electrolyte.

[0016] Preferably, the electrolyte comprises an organic solvent, the organic solvent comprising a cyclic carbonate, a chain carbonate and a chain carboxylate in a mass ratio of 1-15:20-75:5-20. The organic solvent as the main component of the electrolyte needs to consider the compatibility with the whole system. The cyclic carbonate, the chain carbonate and the chain carboxylate selected by the present application to meet the above mass ratio requirements as the organic solvent can provide a suitable medium for the functional additive A, so that the electrolyte has good chemical stability and relative dielectric constant, and the compatibility and stability of the solvent with the various additives are high, which provides a stable and balanced mixed solvent system for the lithium ion battery.

[0017] Preferably, the cyclic carbonate comprises at least one of ethylene carbonate (EC), propylene carbonate (PC) and fluoroethylene carbonate (FEC).

[0018] Preferably, the chain carbonate comprises at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC).

[0019] Preferably, the chain carboxylate comprises at least one of methyl acetate (MA), ethyl acetate (EA), methyl formate (MF), methyl propionate (MP), ethyl propionate (EP), methyl butyrate (MB), ethyl butyrate (EB) and ethyl difluoroacetate (DFAE).

[0020] Preferably, the chain carboxylate comprises ethyl difluoroacetate (DFAE). The use of DFAE as the chain carboxylate is conducive to the participation of the electrolyte in the cycle at high working voltage, and can improve the wide temperature range performance of the electrolyte, while also promoting the CEI film formed by the functional additive A to have good flexibility and mechanical strength, thereby reducing the possibility of damage and cracking of the CEI film, and effectively inhibiting the dissolution of transition metal ions, effectively improving the cycle performance of the battery.

[0021] Preferably, the electrolyte further comprises a film-forming additive, the film-forming additive comprising at least one of vinylene carbonate and fluoroethylene carbonate. By introducing the above film-forming additive into the electrolyte containing the functional additive A, it is conducive to simultaneously improving the cycle stability of the positive electrode and the negative electrode. In the case that the functional additive A preferentially undergoes redox reaction on the positive electrode surface, the above film-forming additive will form an SEI film on the negative electrode surface. Through this complementary protection mechanism, it helps to enhance the structural stability of the SEI film and the CEI film, not only providing effective protection for the positive electrode and the negative electrode, reducing the unintended reaction between the electrolyte and the electrode, but also reducing the impedance of lithium ions crossing the positive and negative electrodes, improving the capacity retention rate of the battery and delaying the cycle life of the battery.

[0022] Preferably, the content of the film-forming additive is 0.1-1% based on the total mass of the electrolyte.

[0023] Preferably, the electrolyte further comprises a lithium salt additive, the lithium salt additive comprising at least one of lithium bisfluorosulfonylimide, lithium difluorophosphate, lithium bisoxalate borate, lithium difluoro oxalate borate, and the content of the lithium salt additive is 0.5% to 1% based on the total mass of the electrolyte. The introduction of the lithium salt additive in the electrolyte in the above-mentioned additive amount is conducive to improving the stability of the interface film, thereby improving the capacity retention rate and cycle performance of the battery, and also improving the overall performance of the electrolyte and the uniformity of the electrolyte distribution in the battery, so as to ensure that the battery has good chemical stability and long service life.

[0024] Preferably, the electrolyte comprises an electrolyte salt, and the content of the electrolyte salt is 10% to 15% based on the total mass of the electrolyte.

[0025] Preferably, the electrolyte salt is lithium hexafluorophosphate.

[0026] According to another aspect of the present application, a lithium ion battery is provided, comprising a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode, and further comprising the above-mentioned electrolyte, and the active material of the positive electrode contains a transition metal element. The use of the positive electrode active material containing a transition metal element in combination with the above-mentioned electrolyte can form a uniform and dense CEI film on the surface of the positive electrode of the battery, greatly optimize the stability of the positive electrode interface, reduce the dissolution of transition metal ions, and at the same time enhance the lithium conductivity of the positive electrode and improve the lithium ion transmission efficiency, so that the battery can maintain excellent cycle stability at a higher working voltage.

[0027] Preferably, the active material of the positive electrode comprises at least one of spinel lithium nickel manganese oxide (LNMO), ternary positive electrode material, lithium cobaltate, layered lithium-rich oxide (LLO), and lithium-rich manganese-based oxide.

[0028] Preferably, the active material of the positive electrode comprises 0.25Li2MnO3·0.75LiMn 0.375 Ni 0.375 Co 0.25 O2. DETAILED DESCRIPTION

[0029] In order to make the person skilled in the art better understand the technical solutions in the present application, the technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor should belong to the scope of protection of the present application.

[0030] Embodiment 1

[0031] The present embodiment provides an electrolyte, which is composed of the following components:

[0032] Table 1. Raw material composition for preparing electrolyte in Example 1

[0033]

[0034]

[0035] Note: The ratio in Table 1 is mass ratio, such as "1.3-propanesultone: 1,3- propenesultone = 1.5:0.5", that is, the mass ratio of 1.3-propanesultone to 1,3- propenesultone is 1.5:0.5, which is combined and matched as a sulfur-containing additive.

[0036] wherein the CAS number of bis (phenylsulfonic acid) peroxide is 29342-61-8, and the structural formula is:

[0037]

[0038] Among the above-mentioned organic solvents, fluoroethylene carbonate (FEC) belongs to cyclic carbonate, diethyl carbonate (DEC) belongs to chain carbonate, and ethyl difluoroacetate (DFAE) belongs to chain carboxylate, so the mass ratio of cyclic carbonate, chain carbonate and chain carboxylate can be calculated as 10:75:15.

[0039] According to the above-mentioned raw material composition, the electrolyte is prepared according to the following steps: in an argon-filled glove box, first mix the above-mentioned functional additive A, sulfur-containing additive, lithium salt additive, film-forming additive and organic solvent, then add electrolyte salt to the organic solvent, mix uniformly at 10°C, and obtain the electrolyte.

[0040] Example 2

[0041] This example refers to the preparation method provided in Example 1 to prepare an electrolyte, and the difference between this example and Example 1 is that: in the process of preparing the electrolyte, equal mass of methanesulfonic peracid anhydride is used instead of the functional additive A used in Example 1, and the rest of the raw material ratio and preparation method are strictly the same as Example 1.

[0042] wherein the CAS number of methanesulfonic peracid anhydride is 1001-62-3, and the structural formula is

[0043]

[0044] Example 3

[0045] This embodiment refers to the preparation method provided in embodiment 1 to prepare an electrolyte, the difference between this embodiment and embodiment 1 is that in the process of preparing the electrolyte, equal mass of bis(trifluoromethylsulfonate) peroxide is used instead of the functional additive A used in embodiment 1, the rest of the raw material ratio, preparation method and embodiment 1 are strictly kept consistent.

[0046] The CAS number of bis(trifluoromethylsulfonate) peroxide is 4079-87-2, and its structural formula is

[0047]

[0048] Embodiment 4

[0049] This embodiment refers to the preparation method provided in embodiment 1 to prepare an electrolyte, the difference between this embodiment and embodiment 1 is that in the process of preparing the electrolyte, equal mass of bis(trifluoromethylsulfonate) peroxide is used instead of the functional additive A used in embodiment 1, the rest of the raw material ratio, preparation method and embodiment 1 are strictly kept consistent.

[0050] The CAS number of bis(trifluoromethylsulfonate) peroxide is 4079-87-2, and its structural formula is

[0051]

[0052] Embodiment 5

[0053] This embodiment refers to the preparation method provided in embodiment 1 to prepare an electrolyte, the difference between this embodiment and embodiment 1 is that in the process of preparing the electrolyte, equal mass of bis(trifluoromethylsulfonate) peroxide is used instead of the functional additive A used in embodiment 1, the rest of the raw material ratio, preparation method and embodiment 1 are strictly kept consistent.

[0054] The CAS number of bis(trifluoromethylsulfonate) peroxide is 4079-87-2, and its structural formula is

[0055] Embodiment 6

[0056] This embodiment refers to the preparation method provided in embodiment 1 to prepare an electrolyte, the difference between this embodiment and embodiment 1 is that in the process of preparing the electrolyte, equal mass of bis(trifluoromethylsulfonate) peroxide is used instead of the functional additive A used in embodiment 1, the rest of the raw material ratio, preparation method and embodiment 1 are strictly kept consistent.

[0057] Embodiment 7

[0058] This example refers to the preparation method provided in Example 1 to prepare an electrolyte, the difference between this example and Example 1 is that in the process of preparing the electrolyte, equal mass of diethyl carbonate is used instead of the organic solvent used in Example 1, i.e. the organic solvent is diethyl carbonate, the rest of the raw material ratio, preparation method and Example 1 are strictly kept consistent.

[0059] Example 8

[0060] This example refers to the preparation method provided in Example 1 to prepare an electrolyte, the difference between this example and Example 1 is that in the process of preparing the electrolyte, equal mass of diethyl carbonate is used instead of the organic solvent used in Example 1, i.e. the organic solvent is diethyl carbonate, the rest of the raw material ratio, preparation method and Example 1 are strictly kept consistent.

[0061] Example 9

[0062] This example refers to the preparation method provided in Example 1 to prepare an electrolyte, the difference between this example and Example 1 is that in the process of preparing the electrolyte, equal mass of diethyl carbonate is used instead of the organic solvent used in Example 1, i.e. the organic solvent is diethyl carbonate, the rest of the raw material ratio, preparation method and Example 1 are strictly kept consistent.

[0063] Comparative Example 1

[0064] This example refers to the preparation method provided in Example 1 to prepare an electrolyte, the difference between this example and Example 1 is that in the process of preparing the electrolyte, equal mass of diethyl carbonate is used instead of the organic solvent used in Example 1, i.e. the organic solvent is diethyl carbonate, the rest of the raw material ratio, preparation method and Example 1 are strictly kept consistent.

[0065] Comparative Example 2

[0066] This example refers to the preparation method provided in Example 1 to prepare an electrolyte, the difference between this example and Example 1 is that in the process of preparing the electrolyte, equal mass of diethyl carbonate is used instead of the organic solvent used in Example 1, i.e. the organic solvent is diethyl carbonate, the rest of the raw material ratio, preparation method and Example 1 are strictly kept consistent.

[0067] Among them, the CAS number of methylene bis (benzenesulfonate) is 1086266-03-6, and its structural formula is

[0068]

[0069] Comparative Example 3

[0070] A comparative example 1 was prepared according to the preparation method provided in example 1. The difference between the comparative example 1 and example 1 is that: in the process of preparing the electrolyte, equal mass of dibenzoyl peroxide was used instead of the functional additive A used in example 1, and the rest of the raw material ratio and preparation method were strictly kept consistent with example 1.

[0071] The CAS number of dibenzoyl peroxide is 94-36-0, and its structural formula is

[0072]

[0073] Preparation example 1

[0074] Lithium ion batteries (soft package batteries) were prepared using the electrolytes provided in examples 1-9 and comparative examples 1-3, respectively. The positive electrode, Celgard2400 separator, and negative electrode were stacked in order, and the cell was obtained by the lamination process. The cell was placed in an outer packaging shell, dried, and injected with electrolyte. After vacuum packaging, standing, formation, and capacity distribution processes, the lithium ion battery was obtained.

[0075] The positive electrode includes a positive electrode current collector and a positive electrode active coating layer. The positive electrode current collector is an aluminum foil, and the positive electrode active coating layer includes a positive electrode active material 0.25Li2MnO3·0.75LiMn 0.375 Ni 0.375 Co 0.25 O2, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF). In the positive electrode active coating layer, the mass ratio of the positive electrode active material, the conductive agent, and the PVDF is 94:3:3. The negative electrode includes a negative electrode current collector and a negative electrode active coating layer. The negative electrode current collector is a copper foil, and the negative electrode active coating layer includes a negative electrode active material graphite, conductive agent acetylene black, carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR). In the negative electrode active coating layer, the mass ratio of the graphite, the conductive agent, the CMC, and the SBR is 94:1:2:3.

[0076] Test example 1

[0077] Test subjects: The electrolytes provided in examples 1-9 and comparative examples 1-3 were used to prepare lithium ion batteries, and the specific preparation method is shown in preparation example 1.

[0078] Test items and test methods:

[0079] (1) Normal temperature cycle performance test:

[0080] The lithium ion battery was charged at 25°C with a constant current of 0.5C (nominal capacity) to a voltage of 4.6V, then charged at 4.6V constant voltage to a current ≤0.05C, after 10 min rest, discharged at 1C constant current to the cut-off voltage 2.5V, the above is one charge-discharge cycle. The lithium ion battery was subjected to 1000 charge-discharge cycles at 25°C according to the above conditions.

[0081] The capacity retention rate (%) of the lithium ion battery after N cycles = (discharge capacity of the Nth cycle / first discharge capacity) x 100%, N is the cycle number of the lithium ion battery.

[0082] The average voltage (V) of the lithium ion battery after N cycles = discharge energy of the Nth cycle / discharge capacity of the Nth cycle, N is the cycle number of the lithium ion battery.

[0083] (2) High temperature cycle performance test:

[0084] The lithium ion battery was charged at 45°C with a constant current of 1.0C (nominal capacity) to a voltage of 4.6V, then charged at 4.6V constant voltage to a current ≤0.05C, after 10 min rest, discharged at 1C constant current to the cut-off voltage 2.5V, the above is one charge-discharge cycle. The lithium ion battery was subjected to 800 charge-discharge cycles at 45°C according to the above conditions.

[0085] The capacity retention rate (%) of the lithium ion battery after N cycles = (discharge capacity of the Nth cycle / first discharge capacity) x 100%, N is the cycle number of the lithium ion battery.

[0086] The average voltage (V) of the lithium ion battery after N cycles = discharge energy of the Nth cycle / discharge capacity of the Nth cycle, N is the cycle number of the lithium ion battery.

[0087] Test results: as shown in Table 2.

[0088] Table 2. Performance test results of each item in this test example

[0089]

[0090] Result analysis:

[0091] Generally speaking, after the lithium ion battery is cycled, there is a battery capacity decay and average voltage drop, so by detecting the capacity retention rate of each battery after cycling, the cycle stability of the battery can be judged, by detecting the average voltage of each battery after cycling, the magnitude of the average voltage drop of the battery after cycling can be judged, and thus the cycle stability of the battery at a higher working voltage and whether the structure of the positive electrode material collapses during the cycle process can be further inferred.

[0092] Comparing the test performances of Examples 1-9 and Comparative Examples 1-3 in Table 1, it can be found that, compared with the lithium ion batteries provided by Comparative Examples 1-3, the lithium ion batteries provided by Examples 1-9 have good cycle stability and thermal stability. Among them, the lithium ion battery provided by Example 1 has higher cycle capacity retention rate and average voltage in normal temperature and high temperature use environment.

[0093] Comparing the comprehensive performance of the lithium ion batteries provided by Examples 1-9 and Comparative Examples 1-3, it can be found that, compared with the lithium ion batteries of Comparative Examples 1-3, the lithium ion batteries provided by Examples 1-9 have higher cycle capacity retention rate and average working voltage in normal temperature and high temperature use environment, which is because the functional additive A containing directly connected sulfonyl and peroxy groups in the molecular structure is introduced into the electrolyte provided by Examples 1-9, which effectively improves the cycle stability and thermal stability of the battery.

[0094] Among them, no functional additive A or material similar in structure is introduced into the electrolyte provided by Comparative Example 1. After the battery provided by Comparative Example 1 is cycled 1000 times in normal temperature or high temperature environment, the concentration of TMs metal ions in the electrolyte is high, and the battery shows poor cycle stability and low working voltage. Comparative Example 2 introduces a compound containing sulfonyl but not containing peroxy group into the electrolyte, and Comparative Example 3 contains a compound containing peroxy group but not containing sulfonyl in the electrolyte. Comparing the experimental data of Comparative Examples 1-3 and Example 1 shown in Table 2, it can be found that, compared with the lithium ion battery of Comparative Example 1, the lithium ion batteries provided by Comparative Examples 2-3 have higher cycle capacity retention rate and average voltage in normal temperature and high temperature environment; but the cycle stability and average voltage of the lithium ion battery of Example 1 are higher than those of the lithium ion batteries of Comparative Examples 2-3 in normal temperature and high temperature. Therefore, when a compound containing sulfonyl is introduced into the electrolyte, or a compound containing peroxy group is introduced into the electrolyte, the cycle stability and thermal stability of the corresponding lithium ion battery can be improved, but the improvement is limited. When the functional additive A containing directly connected sulfonyl and peroxy groups in the molecular structure is introduced into the electrolyte, the cycle stability and thermal stability of the battery reach a better level, that is, the sulfonyl and peroxy groups have a certain synergistic effect when they are directly connected, which can effectively reduce the concentration of TMs metal ions in the electrolyte.

[0095] Comparing the performance indexes of the lithium ion batteries provided by examples 1-5, it can be found that, compared with the lithium ion batteries of examples 2-3, the lithium ion batteries of examples 1, 4 and 5 have better cycle stability and higher average voltage at high temperature, that is, by introducing the functional additive A containing benzene ring into the electrolyte, and the benzene ring in the functional additive A is connected with the peroxy group through the sulfonyl group, examples 1, 4 and 5 help to improve the cycle stability of the battery at room temperature and high temperature, and slow down the decay of the working voltage.

[0096] Comparing the lithium ion batteries provided by example 1 and examples 6-7, it can be found that the solvent of the electrolyte in example 6 is cyclic carbonate and chain carboxylic acid ester, the solvent of the electrolyte in example 7 is chain carbonate, and the solvent of the electrolyte in example 1 includes chain carbonate, cyclic carbonate and chain carboxylic acid ester. Through the performance comparison in table 2, it can be found that the cycle stability of the batteries of examples 6 and 7 is similar, but the cycle stability of the battery of example 1 at room temperature and high temperature is better than that of examples 6 and 7. This shows that there is a certain synergistic effect among chain carbonate, cyclic carbonate and chain carboxylic acid ester, which can simultaneously improve the chemical stability, thermal stability and relative dielectric constant of the electrolyte, and further improve the cycle stability of the battery at room temperature and high temperature.

[0097] The above examples are only used to illustrate the technical solutions of the present application, but not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the essence and scope of the technical solutions of the present application.

Claims

1. An electrolyte, characterized in that, The electrolyte includes functional additive A, and the molecular structure of functional additive A satisfies formula I: R1 and R2 are each independently selected from substituted or unsubstituted alkyl groups, substituted or unsubstituted cycloalkyl groups, and substituted or unsubstituted aryl groups; when substituted, the substituent includes at least one of alkyl, alkoxy, and halogen atoms.

2. The electrolyte as described in claim 1, characterized in that, The molecular structure of the functional additive A satisfies formula II: Among them, R3~R 12 Each is independently selected from hydrogen, alkyl, alkoxy, haloalkyl, and haloalkoxy, and the R3 to R4 groups are... 12 The number of carbon atoms in it does not exceed 10.

3. The electrolyte as described in claim 2, characterized in that, The functional additive A includes bis(benzenesulfonic acid) peroxide.

4. The electrolyte as described in claim 1, characterized in that, Based on the total mass of the electrolyte, the content of the functional additive A is 0.3% to 1%.

5. The electrolyte as described in claim 1, characterized in that, The electrolyte includes an organic solvent, which comprises cyclic carbonates, chain carbonates, and chain carboxylic acid esters in a mass ratio of 1–15:20–75:5–20.

6. The electrolyte as described in claim 5, characterized in that, The chain carbonate includes diethyl carbonate, and the chain carboxylic acid ester includes ethyl difluoroacetate.

7. The electrolyte as described in claim 1, characterized in that, The electrolyte also includes sulfur-containing additives, which include at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, and vinyl sulfate.

8. The electrolyte as described in claim 1, characterized in that, The electrolyte also includes film-forming additives, which include at least one of vinylene carbonate and fluoroethylene carbonate.

9. The electrolyte as described in claim 1, characterized in that, The electrolyte also includes lithium salt additives, which include at least one of lithium difluorosulfonylimide, lithium difluorophosphate, lithium dioxalate borate, and lithium difluorooxalate borate. The content of the lithium salt additives is 0.5% to 1% based on the total mass of the electrolyte.

10. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and a membrane disposed between the positive electrode and the negative electrode, and also includes the electrolyte as described in any one of claims 1 to 9, wherein the active material of the positive electrode contains a transition metal element.

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