A local high-concentration electrolyte for fast-charging lithium battery and preparation method thereof, and lithium-ion battery

Abstract

The present invention discloses a local high-concentration electrolyte for fast-charging lithium batteries and a preparation method thereof, and a lithium-ion battery, and belongs to the technical field of electrolyte preparation. The local high-concentration electrolyte of the present invention includes a local high-concentration electrolyte including a lithium salt, a solvent, a diluent, and an additive; in the local high-concentration electrolyte, the concentration of the lithium salt is 1‑4 mol / L; the diluent is a benzene diluent; the structural formula of the diluent is selected from at least one of formulas I‑IV: #imgabs0# wherein R1, R2, and R3 are independently selected from C1‑C6 alkyl groups, and 0≤n≤4. The local electrolyte of the present invention uses a benzene solvent as a diluent, which reduces the viscosity of the electrolyte while maintaining the unique solvation structure of the high-concentration electrolyte; it can effectively increase the number of lithium ion migrations, improve the fast-charging performance of the battery, reduce the thickness of the organic layer during the formation of the SEI layer, and improve the structural stability of the SEI layer, so that the battery still has a high capacity retention rate in the later stage of the cycle, and also degrades the cost of lithium salts.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolyte preparation, and in particular to a local high-concentration electrolyte for a fast-charging lithium battery and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] FFC charging is a bold fast charging strategy. The traditional solution uses constant current-constant voltage charging. The final constant voltage trickle charge takes a long time. In the constant current charging stage, the charging voltage is increased (exceeding the limit voltage), and the corresponding cutoff current is also increased, which can greatly shorten the time used in the constant voltage stage. However, charging lithium-ion batteries at high rates will cause many problems. The polarization of various battery materials (electrolytes, electrodes) will limit the available capacity of the charge; the overpotential in lithiated graphite during fast charging can cause the electrode potential to be higher than that of Li + / Li 0 The voltage drops below 0 V and leads to Li metal deposition, which seriously affects the battery life. In addition, when a large current is applied, Li is established in the electrolyte phase. + concentration gradient. In extreme cases, Li + will be depleted at the back of the negative electrode, again limiting the available capacity under fast charging conditions, and the concentration gradient and Li + Depletion increases as the electrodes become thicker and less porous.

[0003] High concentration electrolyte (HCE) (>3 mol / L) is formed by simply increasing the ratio of lithium salt to solvent in the electrolyte. -1 ), compared with the traditional concentration (1moL L -1 ) electrolyte has more obvious comprehensive performance advantages (Chemical Communications, 2013, 49(95):11194-11196). Anions in high-concentration electrolytes will enter the first solvation layer and react with Li + The formation of contact ion pairs (CIPs) and aggregated groups (AGGs) can easily form a stable inorganic SEI layer, thereby inhibiting the continuous decomposition of the electrolyte; in addition, the solvent molecules and Li + The coordination number of the electrolyte increases, which reduces the amount of free solvent and effectively reduces the contact between the free solvent and the high-voltage positive electrode. The high migration number brought by the high-concentration electrolyte, the low polarization at the electrolyte / graphite interface, and the high concentration of Li + The excellent SEI structure can effectively improve the high voltage resistance and rate performance of the battery. However, the high viscosity of the high-concentration electrolyte and the high cost caused by the high content of lithium salt have seriously hindered its practical application.

[0004] Based on the excellent performance of high-concentration electrolytes, the concept of local high-concentration electrolytes has gradually emerged. This method mainly involves the use of non-polar solvents or electrolytes that do not react with Li+ The coordinated organic solvent is added as a diluent to the high-concentration electrolyte to reduce its concentration to the normal concentration, but it has a solvation structure similar to that of the high-concentration electrolyte. The local high-concentration electrolyte can maintain the unique solvation effect of high concentration while reducing the viscosity of the electrolyte and the cost of salt. These advantages make the local high-concentration electrolyte easier for industrial applications. Further providing more new local high-concentration electrolytes with better performance to improve the fast-charge cycle performance of lithium batteries is an urgent problem to be solved in this field. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention provides a local high-concentration electrolyte for fast-charging lithium batteries and a preparation method thereof, and a lithium-ion battery. The preparation method of the local electrolyte of the present invention is simple, and a benzene solvent is used as a diluent, which not only maintains the unique solvation structure of the high-concentration electrolyte, but also reduces the viscosity of the electrolyte; at the same time, it reduces the cost of lithium salts, and can also effectively increase the number of lithium ion migration, improve the fast-charging performance of the battery, reduce the thickness of the organic layer during the formation of the SEI layer, and improve the structural stability of the SEI layer, so that the battery still has a high capacity retention rate in the later stage of the cycle.

[0006] The technical solution of the present invention is as follows:

[0007] A first aspect of the present invention provides a local high concentration electrolysis, wherein the local high concentration electrolyte comprises a lithium salt, a solvent, a diluent, and an additive;

[0008] In the local high-concentration electrolyte, the concentration of the lithium salt is 1-4 mol / L;

[0009] The diluent is a benzene diluent;

[0010] The structural formula of the diluent is selected from at least one of Formulas I-IV:

[0011]

[0012]

[0013] Wherein, R1, R2, and R3 are independently selected from H and C1-C6 alkyl;

[0014] The n satisfies: 0≤n≤4.

[0015] Preferably, the C1-C6 alkyl group includes at least one of a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a hexyl group, and a 2-methylpentyl group.

[0016] Preferably, at least two of R1, R2, and R3 are the same.

[0017] Preferably, said R1, R2, and R3 are completely different.

[0018] Preferably, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, and lithium perchlorate;

[0019] and / or, the solvent comprises at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate;

[0020] And / or, the additive includes at least one of fluoroethylene carbonate, vinylene carbonate, difluoroethylene carbonate, trimethyl phosphate, ethyl hexafluorophosphate, and propyl pentafluorophosphate.

[0021] Preferably, the mass fraction of the additive in the electrolyte is 0.1-10%;

[0022] And / or, in the electrolyte, the solvent accounts for 20-80% of the total mass of the solvent and the diluent.

[0023] Preferably, the solvent comprises at least three of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate;

[0024] The additive consists of vinylene carbonate and fluoroethylene carbonate; the mass ratio of the vinylene carbonate to the fluoroethylene carbonate is 1-2:3-8.

[0025] The second aspect of the present invention protects a method for preparing the local high-concentration electrolyte described in the first aspect, and the preparation method comprises the following steps:

[0026] S1: mixing a solvent and an additive to obtain a pretreatment solvent;

[0027] S2: adding lithium salt to the pre-treatment solvent of step S1 to obtain an electrolyte precursor solution;

[0028] S3: adding a diluent to the electrolyte precursor solution of S2 to obtain a locally high-concentration electrolyte;

[0029] In step S2, the concentration of the lithium salt in the electrolyte precursor solution is 2-10 mol / L;

[0030] In step S3, the concentration of the lithium salt in the local high-concentration electrolyte is 1-4 mol / L.

[0031] The third aspect of the present invention protects a lithium ion battery, comprising a positive electrode, a negative electrode, and an electrolyte; the electrolyte is the local high concentration electrolyte described in the second aspect or the local high concentration electrolyte prepared by the preparation method described in the first aspect;

[0032] The positive electrode active material of the positive electrode is LiNixMnyCozO2; wherein 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z≤1.

[0033] Preferably, the lithium-ion battery is a fast-charge lithium-ion battery; the charging method of the fast-charge lithium-ion battery is: constant current and constant voltage charging to a charging cut-off voltage of 0.02-0.05V exceeding the lithium-ion battery, and the cut-off current is increased to 0.7C; the lithium battery is charged using the FFC fast charging method, discharged at 4C, the number of cycles at room temperature is greater than 300 weeks, and the capacity retention rate is greater than 80%.

[0034] The beneficial technical effects of the present invention are:

[0035] The local high concentration electrolyte of the present invention selects a benzene solvent as a diluent, and the F atom of the benzene solvent is not directly connected to the benzene ring, thereby avoiding the problem of difficulty in the leaving of the active group. At the same time, the contained tert-butyl group has a strong electron donating ability, which can increase the electron cloud density of the functional substituent (such as trifluoromethanesulfonic acid group), increase its reaction activity, and make the active group more likely to leave, thereby improving the film forming effect of the SEI film, optimizing the product ion conduction effect, making the structure more stable, and the solid-liquid phase kinetic transmission effect better; at the same time, the used diluent not only maintains the unique solvation structure of the high concentration electrolyte, but also reduces the viscosity of the electrolyte, which can effectively increase the number of lithium ion migration and improve the fast charging performance of the battery. Compared with the high concentration electrolyte, the present invention greatly reduces the cost of lithium salts; in addition, due to the increase in the relative concentration of lithium salts, the ability of anions and solvent molecules (such as EC) to compete for coordination during the solvation process is enhanced, and the thickness of the organic layer in the SEI layer can be effectively reduced during the SEI formation process, thereby improving the structural stability of the SEI layer, so that the battery still has a high capacity retention rate in the later stage of the cycle; at the same time, Li + The energy barrier of the desolvation process is reduced, and Li + The faster migration speed can also reduce the impact of SEI layer thickening on the fast charging performance of the battery in the later stages of the cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The graph is a relationship between the capacity retention rate of battery A after 800 cycles and the number of cycles in Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be described in detail below in conjunction with the embodiments.

[0038] In order to improve the fast charging performance of lithium batteries, the present invention provides a formula of a local high concentration electrolyte, by using a +The coordinated benzene solvent is used as a diluent, which reduces the viscosity of the electrolyte while maintaining the unique solvation structure of the high-concentration electrolyte, effectively improving the Li + The migration number is increased, thereby improving the rate performance of the lithium battery, so that the lithium battery can still maintain good fast charging and discharging performance in the later stage of the cycle.

[0039] The first aspect of the present invention provides a local high concentration electrolysis, wherein the local high concentration electrolyte comprises a lithium salt, a solvent, a diluent, and an additive; in the local high concentration electrolyte, the concentration of the lithium salt is 1-4 mol / L, including but not limited to 1 mol / L, 2 mol / L, 3 mol / L, and 4 mol / L. The diluent is a benzene diluent; the structural formula of the diluent is selected from at least one of formulas I-IV:

[0040]

[0041] Wherein, R1, R2, and R3 are independently selected from H and C1-C6 alkyl;

[0042] The C1-C6 alkyl group includes, but is not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, and 2-methylpentyl. It is understood that the C1-C6 alkyl group of the present invention may include all isomers of the above-mentioned propyl, butyl, pentyl, and hexyl groups. Illustratively, the C1-C6 alkyl group includes at least one of -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH3)2, -CH2CH2CH2CH3, -CHCH3CH2CH3, -CH2CH(CH3)2, -C(CH3)3, -(CH2)4CH3, -C(CH3)2CH2CH3, -CHCH3CH2CH2CH3, -CCH3(CH2CH3)CH3, -CH2CHCH3CH2CH3, -CH2C(CH3)3, -CH2CH2CH(CH3)2, and -CH(CH2CH3)2; and n satisfies: 0≤n≤4, and n includes at least one of 0, 1, 2, 3, and 4.

[0043] It can be understood that the local high concentration electrolyte of the present invention does not directly connect to the benzene ring by selecting a benzene solvent as the diluent, thereby avoiding the problem of difficulty in the active group leaving. At the same time, the tert-butyl group contained has a strong electron donating ability, which can increase the electron cloud density of the functional substituent (such as trifluoromethanesulfonic acid group), increase its reaction activity, and make the active group leave more easily, thereby improving the film forming effect of the SEI film, optimizing the product ion conduction effect, making the structure more stable, and the solid-liquid phase kinetic transmission effect better; at the same time, the diluent used not only maintains the unique solvation structure of the high concentration electrolyte, but also reduces the viscosity of the electrolyte, which can effectively increase the number of lithium ion migration and improve the fast charging performance of the battery. Compared with the high concentration electrolyte, the present invention greatly reduces the cost of lithium salts; in addition, due to the increase in the relative concentration of lithium salts, the ability of anions and solvent molecules (such as EC) to compete for coordination during the solvation process is enhanced, and the thickness of the organic layer in the SEI layer can be effectively reduced during the SEI formation process, and the structural stability of the SEI layer is improved, so that the battery still has a high capacity retention rate in the later stage of the cycle; at the same time, Li + The energy barrier of the desolvation process is reduced, and Li + The faster migration speed can also reduce the impact of SEI layer thickening on the fast charging performance of the battery in the later stages of the cycle.

[0044] In some embodiments, at least two of the R1, R2, and R3 are the same. Exemplarily, the R1 and R3 are the same, and R2 is different; and / or, the R1 and R2 are the same, and R3 is different; and / or, the R2, R3, and R1 are different.

[0045] In some embodiments, R1, R2, and R3 are completely different.

[0046] In some embodiments, the diluent includes at least one of p-tert-butyltrifluoromethanesulfonate benzene, p-tert-butyltrimethylsiloxybenzene, p-tert-butyltrifluoromethoxybenzene, and 3,5-bis-tert-butyltrimethylsiloxybenzene.

[0047] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, and lithium perchlorate. Preferably, the lithium salt is lithium hexafluorophosphate.

[0048] In some embodiments, the solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0049] In some embodiments, the solvent includes at least three of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0050] In some embodiments, the solvent consists of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate; the mass ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate is 1:1-3:2-6, including but not limited to 1:1:6, 1:1:2, 1:3:2, 1:3:6, and 1:2:4.

[0051] It is understandable that in the present invention, when the solvent is ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate, the carbonate has a high reduction potential and is more likely to precipitate and form a SEI film when the negative electrode potential is reduced. Further, by limiting the ratio of the three solvents, the ratio of the carbonate is optimized, and the disadvantage of ethylene carbonate being easily oxidized in the ternary system is improved. If it is not within this range, the cycle performance of the battery corresponding to the obtained electrolyte will be significantly reduced.

[0052] In some embodiments, the additive includes at least one of fluoroethylene carbonate, vinylene carbonate, difluoroethylene carbonate, trimethyl phosphate, ethyl hexafluorophosphate, and propyl pentafluorophosphate.

[0053] In some embodiments, the additive consists of vinylene carbonate and fluoroethylene carbonate; the mass ratio of vinylene carbonate to fluoroethylene carbonate is 1-2:3-8.

[0054] It is understandable that in the present invention, when the additives are vinylene carbonate and fluoroethylene carbonate, the low temperature performance of the battery can be improved, and the high voltage performance is also beneficial. However, fluoroethylene carbonate is not stable enough at high temperatures, produces more gas at high temperatures, and the battery is easily deformed. Further, the ratio of the two additives is limited, the proportion of FEC is optimized, and the shortcomings of such film-forming additives that are unstable at high temperatures and easy to produce gas are improved. If it is not within this range, the high temperature storage performance of the battery corresponding to the obtained electrolyte will be significantly reduced.

[0055] In some embodiments, the mass fraction of the additive in the electrolyte is 0.1-10%, including but not limited to 0.1%, 0.5%, 1%, 2%, 4%, 6%, 8%, 10%;

[0056] In some embodiments, in the electrolyte, the solvent accounts for 20-80% of the total mass of the solvent and the diluent, including but not limited to 20%, 40%, 60%, and 80%.

[0057] It is understandable that polar solvent molecules tend to react with Li + coordination, thus weakening the Li + In the present invention, as the salt concentration (relative to the solvent) increases, the anions tend to compete with the solvent molecules to form Li +The regulated coordination structure is then used to construct a local high-concentration system.

[0058] The second aspect of the present invention provides a method for preparing the local high concentration electrolyte according to the first aspect, the preparation method comprising the following steps:

[0059] S1: mixing a solvent and an additive to obtain a pretreatment solvent;

[0060] S2: adding lithium salt to the pre-treatment solvent of step S1 to obtain an electrolyte precursor solution;

[0061] S3: Adding a diluent to the electrolyte precursor solution of S2 to obtain a locally high-concentration electrolyte.

[0062] In some embodiments, step S1 is performed in a closed environment under nitrogen or argon protection, and the solvent is Molecular sieves remove water.

[0063] In some embodiments, in step S2, the concentration of the lithium salt in the electrolyte precursor solution is 2-10 mol / L, including but not limited to 2 mol / L, 4 mol / L, 6 mol / L, 8 mol / L, and 10 mol / L; in step S3, the concentration of the lithium salt in the local high concentration electrolyte is 1-4 mol / L, including but not limited to 1 mol / L, 2 mol / L, 3 mol / L, and 4 mol / L.

[0064] The third aspect of the present invention provides a lithium ion battery, comprising a positive electrode, a negative electrode, and an electrolyte; the electrolyte is the local high concentration electrolyte described in the first aspect or the local high concentration electrolyte prepared by the preparation method described in the second aspect;

[0065] In some embodiments, the positive electrode active material of the positive electrode is LiNixMnyCozO2; wherein 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z≤1.

[0066] In some embodiments, the negative electrode includes at least one of a graphite negative electrode, a silicon-carbon negative electrode, and a silicon-oxygen negative electrode.

[0067] In some embodiments, the lithium-ion battery is a fast-charge lithium-ion battery; the charging method of the fast-charge lithium-ion battery is: constant current and constant voltage charging to a voltage exceeding the charging cut-off voltage of the lithium-ion battery by 0.02-0.05V, and the cut-off current is increased to 0.7C;

[0068] In some embodiments, the lithium battery is charged using the FFC fast charging method, discharged at 4C, has a cycle number of more than 300 cycles at room temperature, and a capacity retention rate of >80%.

[0069] The present invention will be further described below by way of examples.

[0070] Embodiment 1:

[0071] A local high concentration electrolyte includes lithium hexafluorophosphate, a solvent, an additive and a diluent. The solvent is a mixture of EC (ethylene carbonate), EMC (ethyl methyl carbonate) and DEC (diethyl carbonate) in a mass ratio of 1:1.5:3; the additive is composed of VC (vinylene carbonate) and FEC (fluoroethylene carbonate), and the diluent is p-tert-butyl trifluoromethanesulfonate benzene.

[0072] In the local high concentration electrolyte, the mass fraction of the solvent is 40.7%, the mass fraction of the diluent is 40.7%, the mass fraction of the additive VC is 1%, and the mass fraction of the additive FEC is 3% by mass percentage; the concentration of lithium hexafluorophosphate in the local high concentration electrolyte is 1.2 mol L -1 .

[0073] The preparation method of the above-mentioned local high concentration electrolyte is as follows:

[0074] (1) Under nitrogen protection, first EC (ethylene carbonate) from which water is removed by molecular sieve, EMC (ethyl methyl carbonate), and DEC (diethyl carbonate) are uniformly mixed in a mass ratio of 1:1.5:3 to obtain a solvent, and then 12.1 g of additive VC (vinylene carbonate) and 36.2 g of additive FEC (fluoroethylene carbonate) are added to 490.8 g of the mixed solvent to obtain a pretreated solvent.

[0075] (2) Then, LiPF6 (lithium hexafluorophosphate) was dissolved in the above-mentioned pretreatment solvent to obtain a lithium salt concentration of 4 mol L -1 of the electrolyte precursor solution.

[0076] (3) Finally, 490.8 g of p-tert-butyl trifluoromethanesulfonate benzene diluent was added to the electrolyte precursor solution of step (2) to obtain a lithium salt concentration of 1.2 mol L -1 A local high-concentration electrolyte was prepared and named electrolyte No. Ⅰ.

[0077] A lithium ion battery containing the above-mentioned local high concentration electrolyte, the preparation method of which comprises the following steps:

[0078] Preparation of 4.2V LiNi 0.8 Co 0.1 Mn 0.1 O2 / silicon carbon soft pack battery; In an argon protection environment, the prepared No. Ⅰ electrolyte was injected into a fully dried 4.2V LiNi 0.8 Co 0.1 Mn0.1 In the O2 / silicon carbon soft pack battery, lithium-ion battery A is obtained after processes such as 45°C storage, high-temperature fixture formation and secondary sealing.

[0079] Example 2

[0080] A local high concentration electrolyte, whose composition and ratio are basically the same as those of Example 1, except that in this embodiment, lithium hexafluorophosphate is replaced by a mixed lithium salt of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, and the molar ratio of lithium hexafluorophosphate to lithium bisfluorosulfonyl imide is 10:1.

[0081] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the lithium salt used is replaced by the lithium salt of this example, and the obtained local high concentration electrolyte is named electrolyte No. II.

[0082] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte is prepared by a method substantially the same as that of Example 1, except that the lithium salt in the electrolyte is the lithium salt of this example. A lithium ion battery B is obtained.

[0083] Example 3

[0084] A local high concentration electrolyte, whose composition and proportion are basically the same as those of Example 1, except that in this embodiment, lithium hexafluorophosphate is replaced by a mixed lithium salt of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide, and lithium difluorooxalate borate, and the molar ratio of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide, and lithium difluorooxalate borate is 20:3:1.

[0085] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the lithium salt used is replaced by the lithium salt of this example, and the obtained local high concentration electrolyte is named electrolyte No. III.

[0086] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte, the preparation method of which is substantially the same as that of Example 1, except that the lithium salt in the electrolyte is the lithium salt of this example. A lithium ion battery C is obtained.

[0087] Example 4

[0088] A local high concentration electrolyte, whose composition and ratio are basically the same as those of Example 1, except that in this embodiment, lithium hexafluorophosphate is replaced by a mixed lithium salt of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide, and lithium difluorooxalate borate, and the molar ratio of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide, and lithium difluorooxalate borate is 15:2:1.

[0089] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the lithium salt used is replaced by the lithium salt of this example, and the obtained local high concentration electrolyte is named electrolyte No. IV.

[0090] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte is prepared in the same manner as in Example 1, except that the lithium salt in the electrolyte is the lithium salt of this example. A lithium ion battery D is obtained.

[0091] Example 5

[0092] A local high concentration electrolyte, whose composition and ratio are basically the same as those of Example 1, except that in this embodiment, lithium hexafluorophosphate is replaced by a mixed lithium salt of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonylimide) and lithium difluorooxalatoborate, and the molar ratio of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonylimide) and lithium difluorooxalatoborate is 10:1:1.

[0093] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the lithium salt used is replaced by the lithium salt of this example, and the obtained local high concentration electrolyte is named electrolyte No. V.

[0094] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte is prepared by a method substantially the same as that of Example 1, except that the lithium salt in the electrolyte is the lithium salt of this example. A lithium ion battery E is obtained.

[0095] Example 6

[0096] A local high concentration electrolyte, whose composition and ratio are basically the same as those of Example 1, except that in this embodiment, lithium hexafluorophosphate is replaced by a mixed lithium salt of lithium hexafluorophosphate, lithium bistrifluoromethylsulfonyl imide, lithium bisfluorosulfonyl imide, and lithium difluorooxalate borate, and the molar ratio of lithium hexafluorophosphate, lithium bistrifluoromethylsulfonyl imide, lithium bisfluorosulfonyl imide, and lithium difluorooxalate borate is 20:3:1:1.

[0097] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the lithium salt used is replaced by the lithium salt of this example, and the obtained local high concentration electrolyte is named electrolyte No. VI.

[0098] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte is prepared in the same manner as in Example 1, except that the lithium salt in the electrolyte is the lithium salt of this example. A lithium ion battery F is obtained.

[0099] Example 7

[0100] A local high concentration electrolyte, whose composition and ratio are basically the same as those of Example 1, except that the mass ratio of the three raw materials in the solvent is changed in this example, and the mass ratio of EC:EMC:DEC is changed to 1:1:3.

[0101] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the solvent used is replaced by the solvent of this example, and the obtained local high concentration electrolyte is named electrolyte No. VII.

[0102] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte is prepared by a method substantially the same as that of Example 1, except that the solvent in the electrolyte is the solvent of this example. A lithium ion battery G is obtained.

[0103] Example 8

[0104] A local high concentration electrolyte, whose composition and ratio are basically the same as those of Example 1, except that the mass ratio of the three raw materials in the solvent is changed in this example, and the mass ratio of EC:EMC:DEC is changed to 1:3:3.

[0105] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the solvent used is replaced by the solvent of this example, and the obtained local high concentration electrolyte is named electrolyte No. VIII.

[0106] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte, the preparation method of which is substantially the same as that of Example 1, except that the solvent in the electrolyte is the solvent of this example. A lithium ion battery H is obtained.

[0107] Example 9

[0108] A local high concentration electrolyte, whose composition and proportion are basically the same as those of Example 1, except that the mass ratio of the three raw materials in the solvent is changed in this example, and the mass ratio of EC:EMC:DEC is changed to 1:1:4.

[0109] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the solvent used is replaced by the solvent of this example, and the obtained local high concentration electrolyte is named electrolyte No. IX.

[0110] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte, the preparation method of which is substantially the same as that of Example 1, except that the solvent in the electrolyte is the solvent of this example. A lithium ion battery I is obtained.

[0111] Example 10

[0112] A local high concentration electrolyte, whose composition and ratio are basically the same as those of Example 1, except that the mass ratio of the three raw materials in the solvent is changed in this example, and the mass ratio of EC:EMC:DEC is changed to 1:1:2.

[0113] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the solvent used is replaced by the solvent of this example, and the obtained local high concentration electrolyte is named electrolyte No. X.

[0114] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte is prepared by a method substantially the same as that of Example 1, except that the solvent in the electrolyte is the solvent of this example. A lithium ion battery J is obtained.

[0115] Embodiment 11

[0116] A local high concentration electrolyte, whose composition and ratio are basically the same as those of Example 1, except that the mass ratio of the three raw materials in the solvent is changed in this example, and the mass ratio of EC:EMC:DEC is changed to 1:3:6.

[0117] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the solvent used is replaced by the solvent of this example, and the obtained local high concentration electrolyte is named electrolyte No. XI.

[0118] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte, the preparation method of which is substantially the same as that of Example 1, except that the solvent in the electrolyte is the solvent of this example. A lithium ion battery K is obtained.

[0119] Example 12

[0120] A local high concentration electrolyte, whose composition and ratio are basically the same as those of Example 1, except that this embodiment changes the proportion of two raw materials in the additive in the local high concentration electrolyte. In this embodiment, the proportions of VC and FEC in the local electrolyte solution are 1wt.% and 8wt.%, respectively.

[0121] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the amount of additive used is replaced by the amount of additive in this example, and the obtained local high concentration electrolyte is named electrolyte No. XII.

[0122] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte is prepared by a method substantially the same as that of Example 1, except that the amount of additive in the electrolyte is the same as that of the present example. A lithium ion battery L is obtained.

[0123] Embodiment 13

[0124] A local high concentration electrolyte, whose composition and ratio are basically the same as those of Example 1, except that this embodiment changes the proportion of two raw materials in the additive in the local high concentration electrolyte. In this embodiment, the proportions of VC and FEC in the local electrolyte solution are 2wt.% and 8wt.%, respectively.

[0125] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the amount of additive used is replaced by the amount of additive in this example, and the obtained local high concentration electrolyte is named electrolyte No. XIII.

[0126] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte is prepared by a method substantially the same as that of Example 1, except that the amount of additive in the electrolyte is the amount of additive in this example, to obtain a lithium ion battery M.

[0127] Embodiment 14

[0128] A local high concentration electrolyte, whose composition and proportion are basically the same as those of Example 1, except that the diluent is replaced by p-tert-butyltrimethylsiloxybenzene in this example.

[0129] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the diluent used is replaced by the diluent of this example, and the obtained local high concentration electrolyte is named electrolyte No. XIV.

[0130] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte is prepared by a method substantially the same as that of Example 1, except that the diluent in the electrolyte is the diluent of this example. A lithium ion battery N is obtained.

[0131] Embodiment 15

[0132] A local high concentration electrolyte, whose composition and proportion are basically the same as those of Example 1, except that the diluent is replaced by tert-butyl trifluoromethoxybenzene in this example.

[0133] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the diluent used is replaced by the diluent of this example, and the obtained local high concentration electrolyte is named electrolyte No. XV.

[0134] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte, the preparation method of which is substantially the same as that of Example 1, except that the diluent in the electrolyte is the diluent of this example. A lithium ion battery O is obtained.

[0135] Example 16

[0136] A local high concentration electrolyte, whose composition and proportion are basically the same as those of Example 1, except that the diluent is changed to 3,5-di-tert-butyltrimethylsiloxybenzene in this example.

[0137] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the diluent used is replaced by the diluent of this example, and the obtained local high concentration electrolyte is named electrolyte No. XVI.

[0138] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte, the preparation method of which is substantially the same as that of Example 1, except that the diluent in the electrolyte is the diluent of this example. A lithium ion battery P is obtained.

[0139] Embodiment 17

[0140] A local high concentration electrolyte, whose composition and ratio are basically the same as those of Example 1, except that the diluent in this embodiment is changed to a mixed diluent of p-tert-butyltrimethylsiloxybenzene and p-tert-butyltrifluoromethoxybenzene, and the molar ratio of p-tert-butyltrimethylsiloxybenzene to p-tert-butyltrifluoromethoxybenzene is 1:1.

[0141] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the diluent used is replaced by the diluent of this example, and the obtained local high concentration electrolyte is named electrolyte No. XVII.

[0142] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte, the preparation method of which is substantially the same as that of Example 1, except that the diluent in the electrolyte is the diluent of this example. A lithium ion battery Q is obtained.

[0143] Embodiment 18

[0144] A local high concentration electrolyte, whose composition and ratio are basically the same as those of Example 1, except that in this embodiment, the diluent is changed to a mixed diluent of 3,5-bis-tert-butyltrimethylsiloxybenzene and p-tert-butyltrifluoromethoxybenzene, and the molar ratio of 3,5-bis-tert-butyltrimethylsiloxybenzene to p-tert-butyltrifluoromethoxybenzene is 3:1.

[0145] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the diluent used is replaced by the diluent of this example, and the obtained local high concentration electrolyte is named electrolyte No. XVIII.

[0146] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte, the preparation method of which is substantially the same as that of Example 1, except that the diluent in the electrolyte is the diluent of this example. A lithium ion battery R is obtained.

[0147] Embodiment 19

[0148] A local high concentration electrolyte, whose composition and proportion are basically the same as those of Example 1, except that the diluent is changed to trifluoromethoxybenzene in this example.

[0149] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the diluent used is replaced by the diluent of this example to obtain the local high concentration electrolyte.

[0150] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte, the preparation method of which is basically the same as that of Example 1, the only difference being that the diluent in the electrolyte is the diluent of this example.

[0151] Embodiment 20

[0152] A local high concentration electrolyte, whose composition and proportion are basically the same as those of Example 1, except that the diluent is replaced by methyl trifluorinated methoxybenzene in this embodiment.

[0153] The preparation method of the above-mentioned local high concentration electrolyte is basically the same as that of Example 1, except that the diluent used is replaced with the diluent of this example to obtain the local high concentration electrolyte.

[0154] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte, the preparation method of which is basically the same as that of Example 1, the only difference being that the diluent in the electrolyte is the diluent of this example.

[0155] Comparative Example 1

[0156] An electrolyte solution, whose composition and proportion are substantially the same as those of Example 1, except that the diluent is changed to 3-fluorotrifluoromethanesulfonate benzene in this comparative example.

[0157] The preparation method of the above-mentioned local high-concentration electrolyte is basically the same as that of Example 1, except that the diluent used is replaced by the diluent of this comparative example to obtain the electrolyte.

[0158] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte, the preparation method of which is basically the same as that of Example 1, the only difference being that the diluent in the electrolyte is the diluent of this comparative example.

[0159] Comparative Example 2

[0160] An electrolyte, whose composition and proportion are basically the same as those of Example 1, except that the diluent is replaced by p-methylbenzene trifluoride in this comparative example.

[0161] The preparation method of the above-mentioned local high-concentration electrolyte is basically the same as that of Example 1, except that the diluent used is replaced by the diluent of this comparative example to obtain the electrolyte.

[0162] A lithium ion battery containing the above-mentioned locally high-concentration electrolyte, the preparation method of which is basically the same as that of Example 1, the only difference being that the diluent in the electrolyte is the diluent of this comparative example.

[0163] Test example:

[0164] The performance tests were carried out on the batteries of each embodiment and comparative example, and the test results are shown in Table 1, where:

[0165] 1. Normal temperature cycle performance

[0166] At 25°C, the lithium-ion battery was charged to 4.23V at 3.5C constant current and constant voltage, with a cut-off current of 0.7C, and then discharged to 2.5V at 4C constant current. After 800 cycles of charge and discharge, the cycle capacity retention rate (%) after the 800th cycle was calculated:

[0167]

[0168] 2. High temperature storage performance

[0169] At room temperature of 25°C, the lithium ion batteries corresponding to the above embodiments and comparative examples were charged to 4.2V at 3.5C constant current and constant voltage, with a cut-off current of 0.05C, and the lithium ion batteries were discharged once at 4C (the discharge capacity was recorded as DC0), and then the batteries were charged to 4.2V at 3.5C constant current and constant voltage (cut-off current of 0.05C); the lithium ion batteries were placed in a 60°C high temperature box for 7 days, and after being taken out, they were discharged at 4C at 25°C (the discharge capacity was recorded as DC1); then 3.5C / 4C charging and discharging were performed at room temperature (the discharge capacity was recorded as DC2), and the residual capacity (i.e., high temperature capacity retention rate, %) and capacity recovery (i.e., high temperature capacity recovery rate, %) of the lithium ion batteries were calculated using the following formula:

[0170]

[0171] Table 1 Lithium ion battery performance test results of each embodiment

[0172]

[0173]

[0174] As can be seen from the above table, the batteries of Examples 1-20 have better cycle performance and capacity retention. Comparative Examples show that, for H or methyl substituted diluents, since the electron donating ability of H and methyl is not as good as that of tert-butyl, the performance of the batteries corresponding to the diluents of Examples 19 and 20 is worse than that of the batteries prepared with other tert-butyl diluents.

[0175] Comparative Examples 1-2 used diluents with different structures. The structure in which the fluorine atom is directly connected to the benzene ring (Comparative Example 1) has a reduced ability of the active group to leave, and the battery's cycle capacity is significantly reduced. The electron-donating ability of the methyl group is weaker than that of the tert-butyl group, and the active group is lacking (Comparative Example 2). The battery's cycle capacity is weaker than that of the tert-butyl structure, but stronger than that of the structure in which the fluorine atom is directly connected to the benzene ring.

[0176] Figure 1 The figure is a graph showing the capacity retention rate of battery A after 800 cycles versus the number of cycles in Example 1 of the present invention, where the solid line represents the capacity retention rate of the battery and the dotted line represents the thickness expansion rate of the battery every 100 cycles. It can be seen from the figure that the battery in Example 1 has good cycle performance.

[0177] The above is only a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. A local high concentration electrolysis, characterized in that: The local high-concentration electrolyte includes lithium salt, solvent, diluent, and additive; In the local high-concentration electrolyte, the concentration of the lithium salt is 1-4 mol / L; The diluent is a benzene diluent; The structural formula of the diluent is selected from at least one of Formulas I-IV: Wherein, R1, R2, and R3 are independently selected from H and C1-C6 alkyl; The n satisfies: 0≤n≤4.

2. The local high concentration electrolysis according to claim 1, characterized in that: The C1-C6 alkyl group includes at least one of a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a hexyl group, and a 2-methylpentyl group.

3. The local high concentration electrolysis according to claim 1, characterized in that: At least two of R1, R2, and R3 are the same.

4. The local high concentration electrolysis according to claim 1, characterized in that: The R1, R2, and R3 are completely different.

5. The local high concentration electrolysis according to claim 1, characterized in that: The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, and lithium perchlorate; and / or, the solvent comprises at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate; And / or, the additive includes at least one of fluoroethylene carbonate, vinylene carbonate, difluoroethylene carbonate, trimethyl phosphate, ethyl hexafluorophosphate, and propyl pentafluorophosphate.

6. The local high concentration electrolysis according to claim 1, characterized in that: The mass fraction of the additive in the electrolyte is 0.1-10%; And / or, in the electrolyte, the solvent accounts for 20-80% of the total mass of the solvent and the diluent.

7. The local high concentration electrolysis according to claim 1, characterized in that: The solvent includes at least three of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate; The additive consists of vinylene carbonate and fluoroethylene carbonate; the mass ratio of the vinylene carbonate to the fluoroethylene carbonate is 1-2:3-8.

8. A method for preparing the local high concentration electrolyte according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: S1: mixing a solvent and an additive to obtain a pretreatment solvent; S2: adding lithium salt to the pre-treatment solvent of step S1 to obtain an electrolyte precursor solution; S3: adding a diluent to the electrolyte precursor solution of S2 to obtain a locally high-concentration electrolyte; In step S2, the concentration of the lithium salt in the electrolyte precursor solution is 2-10 mol / L; In step S3, the concentration of the lithium salt in the local high-concentration electrolyte is 1-4 mol / L.

9. A lithium ion battery, characterized in that: Including positive electrode, negative electrode and electrolyte; The electrolyte is the local high concentration electrolyte according to any one of claims 1 to 7 or the local high concentration electrolyte prepared by the preparation method according to claim 8; The positive electrode active material of the positive electrode is LiNixMnyCozO2; wherein 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z≤1.

10. The lithium ion battery according to claim 9, characterized in that: The lithium-ion battery is a fast-charge lithium-ion battery; the charging method of the fast-charge lithium-ion battery is: constant current and constant voltage charging until the charging cut-off voltage of the lithium-ion battery exceeds 0.02-0.05V, and the cut-off current is increased to 0.7C; The lithium battery is charged using the FFC fast charging method and discharged at 4C, the number of cycles at room temperature is greater than 300 weeks, and the capacity retention rate is greater than 80%.

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