CN113363583B

CN113363583B - Electrolyte additive, non-aqueous electrolyte and lithium ion battery thereof

Info

Publication number: CN113363583B
Application number: CN202110716621.XA
Authority: CN
Inventors: 白晶; 毛冲; 王霹霹; 潘东优; 欧霜辉; 黄秋洁; 戴晓兵
Original assignee: Zhuhai Smoothway Electronic Materials Co Ltd
Current assignee: Zhuhai Smoothway Electronic Materials Co Ltd
Priority date: 2021-06-25
Filing date: 2021-06-25
Publication date: 2022-05-10
Anticipated expiration: 2041-06-25
Also published as: CN113363583A; WO2022267391A1

Abstract

The invention discloses an electrolyte additive, a non-aqueous electrolyte and a lithium ion battery thereof, wherein the electrolyte additive is added with the non-aqueous electrolyteAn additive comprising a compound of formula A,

wherein R is sulfonyl fluoride or trifluoromethyl sulfonyl. The electrolyte additive has high solubility and good wettability, and can greatly improve the low-temperature cycle performance of the lithium ion battery under the condition of not increasing impedance.

Description

Electrolyte additive, non-aqueous electrolyte and lithium ion battery thereof

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte additive, a non-aqueous electrolyte and a lithium ion battery thereof.

Background

The lithium ion battery has the advantages of high working voltage, high energy density, long service life, wide working temperature range, environmental friendliness and the like, and is widely applied to the fields of 3C digital products, electric tools, electric automobiles, aerospace and the like. With the demand for batteries becoming higher and higher, the development trend of batteries is light, thin and high energy density, especially for 3C digital products, such as mobile phone batteries, tablet computers and camera devices. The conventional common commercial lithium ion positive electrode materials include lithium iron phosphate, lithium cobaltate, nickel cobalt manganese ternary materials and the like, and although the theoretical capacities of various positive electrode materials are relatively large, the energy density is not high enough because the cut-off voltages of the positive electrode materials are 4.2V and lower.

With the increasing demand of the market for high energy density lithium ion batteries, increasing the charge cut-off voltage of the positive electrode material is an effective means for increasing the energy density, such as the voltage of a commercial lithium cobalt oxide battery 4.2V → 4.35V → 4.4V → 4.45V → 4.48V → 4.5V, but increasing the charge cut-off voltage (≧ 4.5V) of the positive electrode material has some problems: for example, the compatibility of a conventional electrolyte used in combination with a positive electrode material under high voltage is extremely poor, the common carbonate-based electrolyte is easily oxidized and decomposed under high voltage, and the generated by-products have negative effects on the performance of the lithium ion battery, so that on one hand, the impedance inside the lithium ion battery is increased, on the other hand, the positive electrode material of the battery is also corroded, and particularly, the low-temperature performance of the lithium ion battery is obviously insufficient at low temperature. Therefore, how to ensure the cycle performance and the high-temperature storage performance of the lithium ion battery under the premise of improving the cut-off voltage of the cathode material becomes a key point of research.

Disclosure of Invention

The invention aims to provide an electrolyte additive which has high solubility and good wettability and can greatly improve the low-temperature cycle performance of a lithium ion battery under the condition of not increasing impedance.

Another object of the present invention is to provide a nonaqueous electrolytic solution capable of improving cycle performance and high-temperature storage performance of a lithium ion battery.

Still another object of the present invention is to provide a lithium ion battery having superior cycle performance and high temperature storage performance.

In order to achieve the above objects, the present invention provides an electrolyte additive comprising a compound represented by formula a,

wherein R is sulfonyl fluoride or trifluoromethyl sulfonyl.

Compared with the prior art, the invention provides an electrolyte additive, which comprises a compound shown as a formula A, wherein the formula A has a special structure, the electrolyte additive has high solubility and good wettability in electrolyte and can fully infiltrate a pole piece in a short time, so the electrolyte additive has good film forming capability, meanwhile, the formula A has a cyclic sulfonamide group and can form an N, S-containing organic compound, the N, S organic compound is attached to the surfaces of a positive electrode and a negative electrode to form a stable SEI film, and when a R group is a sulfonyl fluoride group or a trifluoromethyl sulfonyl group, the sulfonyl fluoride group and the trifluoromethyl sulfonyl group can regulate and control LiSO (LiSO) in the film₃、ROSO₂Ratio of sulfur-containing compound such as LiFor example, compounds such as LiF and lithium fluorosulfonate are additionally generated to further increase the ionic conductivity of the SEI film, thereby reducing the resistance of the SEI film, so that the lithium ion battery has better low-temperature cycle performance. Therefore, the compound shown in the formula A has high solubility and good wettability, and can greatly improve the low-temperature cycle performance of the lithium ion battery under the condition of not increasing impedance.

Specifically, when the R group is sulfonyl fluoride, the formula A is ASE-FSI, and the structural formula is shown as follows; when the R group is trifluoromethyl sulfonyl, the formula A is ASE-TFSI, and the structural formula is shown as follows:

specifically, ASE-FSI, ASE-TFSI can be prepared by the following synthetic routes:

in order to achieve the above purpose, the present invention provides a nonaqueous electrolyte solution, which includes a lithium salt, a nonaqueous organic solvent, and the above electrolyte additive, wherein the mass percentage of the electrolyte additive in the nonaqueous electrolyte solution is 0.5-5%.

Compared with the prior art, the non-aqueous electrolyte disclosed by the invention comprises a high-content compound shown as a formula A, wherein the formula A has a special structure, and the electrolyte additive has high solubility and good wettability in the electrolyte and can fully infiltrate a pole piece in a short time, so that the electrolyte additive has good film forming capability; meanwhile, when the R group is sulfonyl fluoride group or trifluoromethyl sulfonyl group, the sulfonyl fluoride group and the trifluoromethyl sulfonyl group can regulate and control LiSO in the SEI film₃、ROSO₂In addition, compounds such as LiF, fluorine-containing lithium sulfonyl and the like are generated in addition to the proportion of the sulfur-containing compounds such as Li and the like, so that the ionic conductivity of the SEI film is further increased, the impedance of the SEI film is reduced, and the low-temperature cycle performance of the lithium ion battery can be improved. The non-aqueous electrolyte can improve the cycle performance and the high-temperature storage performance of the lithium ion battery, so that the non-aqueous electrolyte has more comprehensive performance.

Preferably, the lithium salt of the present invention is at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis (oxalato) borate, lithium difluoro (oxalato) phosphate, lithium tetrafluoro (oxalato) borate, lithium tetrafluoro (oxalato) phosphate, lithium bis (trifluoromethylsulfonyl) imide, lithium bis (fluorosulfonato) imide and lithium tetrafluoro (malonato) phosphate.

Preferably, the mass percentage of the lithium salt in the non-aqueous electrolyte is 10-20%. Specifically but not limited to 10%, 12%, 15%, 18%, 20%.

Preferably, the non-aqueous organic solvent of the present invention is at least one of Ethylene Carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), propylene carbonate, butyl acetate, γ -butyrolactone, propyl propionate, ethyl propionate, and ethyl butyrate.

Preferably, the mass percentage of the nonaqueous organic solvent in the nonaqueous electrolyte solution is 60-80%. Specific but not limited to 60%, 65%, 70%, 75%, 80%.

Preferably, the nonaqueous electrolyte solution further comprises an auxiliary agent, the auxiliary agent is at least one of 2,2, 2-trifluoroethyl carbonate, ethyl propyl 2,2, 2-trifluoroparbonate, Vinylene Carbonate (VC), fluoroethylene carbonate (FEC), vinyl Difluorocarbonate (DFEC), diethyl pyrocarbonate, 1, 3-Propane Sultone (PS), vinyl sulfate (DTD), tris (trimethylsilane) phosphate, tris (trimethylsilane) phosphite, 4 '-bis-1, 3-dioxolane-2, 2' -dione (BDC), 3-divinyl disulfate (BDTD), triallyl phosphate, triallyl propargyl phosphate, succinonitrile, adiponitrile, 1,3, 6-hexanetricarbonitrile and 1, 2-bis (cyanoethoxy) ethane.

Preferably, the mass percentage of the auxiliary agent in the nonaqueous electrolyte is 2-10.5%. Specifically but not limited to 2%, 5%, 7%, 9%, 10.5%.

In order to achieve the above object, the present invention provides a lithium ion battery comprising a positive electrode material and a negative electrode material, further comprising the above nonaqueous electrolytic solution, and having a maximum charging voltage of 4.53V.

Compared with the prior art, the non-aqueous electrolyte of the lithium ion battery comprises the compound shown in the formula A, the formula A has a special structure, the solubility in the electrolyte is higher, the pole piece can be fully soaked in a short time, the formula A can form an N, S-containing organic compound, the N, S organic compound is attached to the surfaces of a positive pole and a negative pole to form a stable SEI film, the SEI film formed when the content of the formula A is higher is thicker, and the normal-temperature cycle performance, the high-temperature cycle performance and the high-temperature storage performance are improved, and meanwhile, when R is sulfonyl fluoride or trifluoromethyl sulfonyl, the sulfonyl fluoride group and the trifluoromethyl sulfonyl group can regulate and control LiSO in the SEI film₃、ROSO₂In addition, compounds such as LiF, fluorine-containing lithium sulfonyl and the like are generated in addition to the proportion of the sulfur-containing compounds such as Li and the like, so that the ionic conductivity of the SEI film is further increased, the impedance of the SEI film is reduced, and the low-temperature cycle performance is also improved. Therefore, the lithium ion battery has better cycle performance and high-temperature storage performance.

Preferably, the positive electrode material of the lithium ion battery is lithium cobaltate.

Preferably, the negative electrode material of the lithium ion battery is natural graphite.

Drawings

FIG. 1 is an initial DCIR plot of lithium ion batteries of examples 1,3,6, 8, 1, and 4-7 capacity-divided lithium ion batteries.

Detailed Description

To better illustrate the objects, technical solutions and advantages of the present invention, the present invention will be further described with reference to specific examples. It should be noted that the following implementation of the method is a further explanation of the present invention, and should not be taken as a limitation of the present invention.

First, solubility experiments of ASE-FSI, ASE-TFSI, ASE-Li and ASE-Et were carried out, and the results are shown in Table 1

Wherein ASE-Li and ASE-Et can be prepared by the following synthetic routes:

solubility test: in a nitrogen-filled glove box (O)₂＜1ppm，H₂O < 1ppm), Ethylene Carbonate (EC), diethyl carbonate (DEC) and Ethyl Methyl Carbonate (EMC) were mixed uniformly in a mass ratio of 1:1:2 to prepare 80.0g of a nonaqueous organic solvent, the mixed solution was sealed, packed, placed in a freezing chamber (-4 ℃) and frozen for 2 hours, and then taken out, and placed in a glove box (O) filled with nitrogen gas₂＜1ppm，H₂O is less than 1ppm), 20g of lithium hexafluorophosphate is slowly added into the mixed solution, and the electrolyte is prepared after uniform mixing. ASE-FSI, ASE-TFSI, ASE-Li and ASE-Et were dissolved in the above electrolytes, respectively, and the mass of the solute dissolved in 100 g of the electrolytes in a saturated state was measured and recorded as S g, and the maximum solubility of each substance was calculated according to the following formula.

The maximum solubility (%) - (S/(S + 100). times.100%

Table 1 solubility results

Additive agent	Maximum solubility
		ASE	0.6％
ASE-Li	0.4％
		ASE-Et	0.6％
ASE-FSI	7.5％
		ASE-TFSI	6.5％

As is clear from the results in Table 1, the solubility of ASE-FSI and ASE-TFSI in the electrolyte was significantly higher than that of ASE, ASE-Li and ASE-Et.

Example 1

In a nitrogen-filled glove box (O)₂＜1ppm，H₂O is less than 1ppm), uniformly mixing ethylene carbonate, diethyl carbonate and methyl ethyl carbonate according to the mass ratio of 1:1:2 to prepare 79g of non-aqueous organic solvent, and then adding 1g of ASE-FSI as an additive to obtain a mixed solution. Sealing, packaging, freezing at a freezing room (-4 deg.C) for 2 hr, taking out, and placing in a nitrogen-filled glove box (O)₂＜1ppm，H₂O < 1ppm), 20g of lithium hexafluorophosphate was slowly added to the mixed solution, and the mixture was uniformly mixed to prepare a nonaqueous electrolytic solution.

The formulations of the nonaqueous electrolytic solutions of examples 2 to 17 and comparative examples 1 to 7 are shown in Table 2, and the procedure for preparing the nonaqueous electrolytic solution is the same as that of example 1.

TABLE 2 nonaqueous electrolyte formulation

Wherein TFSI is trifluoromethyl sulfonamide, the structural formula is shown as follows:

lithium cobaltate with the highest charging voltage of 4.53V is used as a positive electrode material, natural graphite is used as a negative electrode material, the electrolytes of examples 1-17 and comparative examples 1-7 are prepared into a lithium ion battery by referring to a conventional lithium battery preparation method, and low-temperature cycle performance, normal-temperature cycle performance, high-temperature cycle performance and high-temperature storage performance are respectively carried out according to the following methods, wherein the test results are shown in Table 3; the lithium ion batteries of examples 1,3,6, 8, 1 and 4 to 7 were subjected to the DCIR test in the initial state, and the test results are shown in fig. 1.

And (3) low-temperature cycle testing:

placing the battery in an oven with constant temperature of-10 ℃, charging to 4.53V at a constant current of 0.5C, then charging to 0.05C at a constant voltage, then discharging to 3.0V at a constant current of 1C, repeating the steps, recording the discharge capacity of the first circle and the discharge capacity of the last circle, and calculating the capacity retention rate according to the following formula:

capacity retention rate ═ last cycle discharge capacity/first cycle discharge capacity × 100%

And (3) testing the normal-temperature cycle performance:

the lithium ion battery is placed in an environment with the temperature of 25 ℃, is charged to 4.53V at a constant current of 1C, is charged at a constant voltage until the current is reduced to 0.05C, is discharged to 3.0V at a constant current of 1C, is circulated, and is subjected to DCIR measurement every 50 circles. The discharge capacity of the first and last turn was recorded, as well as the DCIR every 50 turns. The capacity retention and DCIR boost for the high temperature cycle were calculated as follows:

DCIR lift-off rate-the last 50 cycles of DCIR/the first cycle of DCIR × 100%.

And (3) testing high-temperature cycle performance:

the cell was placed in an oven at a constant temperature of 45 ℃, charged to 4.53V at a constant current of 1C, then charged at a constant voltage to a current of 0.05C, and then discharged to 3.0V at a constant current of 1C, cycled through this cycle, and then DCIR was measured every 50 cycles. The discharge capacity of the first and last turn was recorded, as well as the DCIR every 50 turns. The capacity retention and DCIR boost for the high temperature cycle were calculated as follows:

DCIR lift-off rate-the last 50 cycles of DCIR/the first cycle of DCIR × 100%.

And (3) testing the high-temperature storage performance:

and (3) charging the formed battery to 4.53V at a constant current and a constant voltage of 1C at normal temperature, measuring the initial discharge capacity and the initial battery thickness of the battery, storing the battery for 8 hours at 85 ℃, then discharging the battery to 3.0V at 1C, and measuring the capacity retention and recovery capacity of the battery and the thickness of the battery after storage. The calculation formula is as follows:

battery capacity retention (%) — retention capacity/initial capacity × 100%;

battery capacity recovery (%) — recovery capacity/initial capacity × 100%;

thickness swell (%) (cell thickness after storage-initial cell thickness)/initial cell thickness x 100%. Initial DCIR testing:

charging the batteries after capacity grading to 4.53V at a constant current and a constant voltage of 1C at normal temperature, then discharging the batteries at a constant current of 0.5C at normal temperature until the charge amount is 50% SOC, standing the batteries for 5min, then discharging the batteries for 1s at 1C, and standing the batteries for 5min, and then discharging the batteries for 10s at 0.1C.

DCIR (voltage after first discharge V1-voltage after second discharge V2)/(first discharge current I1-second discharge current I2)

TABLE 3 cycling and high temperature storage Performance results

From the results in table 3, it can be seen that the low-temperature cycle performance of examples 1 to 17 is significantly better than that of comparative examples 1 to 7, because the compound shown in formula a is used as the electrolyte additive, the electrolyte additive has high solubility in the electrolyte, good wettability, and can sufficiently wet the electrode sheet in a short time, so that the electrolyte additive has good film forming capability, meanwhile, the cyclic sulfonamide group in formula a can form an organic compound containing N, S, the organic compound of N, S is attached to the surfaces of the positive electrode and the negative electrode to form a stable SEI film, and the sulfonyl fluoride group in the ASE-FSI and the trifluoromethyl sulfonyl group in the ASE-TFSI can regulate and control LiSO in the SEI film₃、ROSO₂In addition, compounds such as LiF, fluorine-containing lithium sulfonyl and the like are generated according to the proportion of the sulfur-containing compounds such as Li and the like, so that the ionic conductivity of the SEI film is further increased, and the aim of reducing the impedance is fulfilled.

From the results in table 3, it is known that the cycle performance and the high-temperature storage performance of examples 1 and 3 to 17 are significantly better than those of comparative examples 1 to 7, because when the nonaqueous electrolytic solution contains a high content of the compound represented by formula a, the compound represented by formula a can sufficiently infiltrate the electrode sheet in a short time, the compound represented by formula a can form an organic composite containing N, S, the organic composite N, S can adhere to the surfaces of the positive electrode and the negative electrode to form a stable SEI film, and the organic composite can form a thicker SEI film when the content of formula a is higher, so that the normal-temperature cycle performance, the high-temperature cycle performance and the high-temperature storage performance of the lithium ion battery can be improved, and meanwhile, when the R group is a sulfonyl fluoride group or a trifluoromethylsulfonyl fluoride group, the sulfonyl fluoride group and the trifluoromethylsulfonyl fluoride group can regulate the proportion of sulfur-containing compounds such as LiSO3, ROSO2Li and the like in the SEI film, and further generate some compounds such as LiF, fluorine-containing sulfonyl lithium and the like to further increase the ionic conductivity of the SEI film, thereby reducing the resistance of the SEI film and thus improving low temperature cycle performance. Therefore, the non-aqueous electrolyte can enable the lithium ion battery to have better cycle performance and high-temperature storage performance.

As is clear from the results in table 3, the effect of example 1 is superior to that of comparative example 7 in that the acid value of the nonaqueous electrolytic solution is too high due to the active hydrogen bonded to the N of ASE and trifluoromethyl sulfonamide, which promotes the decomposition of the nonaqueous electrolytic solution to generate HF, and the ASE and trifluoromethyl sulfonamide, although forming a film, consume too much lithium salt, which results in too low conductivity of the electrolytic solution and deterioration of various properties, and the generated hydrofluoric acid corrodes the positive and negative electrodes to deteriorate the battery performance.

As is clear from tables 1 and 3 and FIG. 1, comparative examples 4 to 6 also contain cyclic sulfonamide groups, but since ASE, ASE-Li and ASE-Et are not highly soluble themselves and have limited film forming ability in the electrolyte, the high temperature cycle performance, the normal temperature cycle performance and the high temperature storage performance are inferior to those of examples 1 and 3 to 19, and since ASE, ASE-Li and ASE-Et do not contain a group which reduces resistance, the low temperature cycle performance is inferior. Therefore, the compound shown in the formula A has high solubility and good wettability, and can greatly improve the low-temperature cycle performance of the lithium ion battery under the condition of not increasing impedance.

From the results in table 3, it is understood that the cycle performance and the high-temperature storage performance of examples 1 and 3 to 17 are better than those of example 2, because the compound represented by formula a cannot inhibit the solvent film formation at a low content, resulting in the co-film formation of the solvent and the additive, and thus the film forming ability of the compound represented by formula a is better at a high content than at a low content, and the SEI film formed by the compound represented by formula a at a high content is more stable than the SEI film formed by the compound represented by formula a at a low content.

From the results in table 3, it can be seen that the cycle performance of examples 8-14 is significantly better than that of example 1, and therefore, the high-low temperature cycle performance and the high-temperature storage performance of the lithium ion battery can be further improved by adding an auxiliary agent or a special lithium salt on the basis of the compound shown in formula a.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. An electrolyte additive is characterized by comprising a compound shown as a formula A,

wherein R is sulfonyl fluoride or trifluoromethyl sulfonyl.

2. The nonaqueous electrolyte solution is characterized by comprising a lithium salt, a nonaqueous organic solvent and the electrolyte additive according to claim 1, wherein the mass percentage of the electrolyte additive in the nonaqueous electrolyte solution is 0.5-5%.

3. The nonaqueous electrolytic solution of claim 2, wherein the lithium salt is at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis (oxalato) borate, lithium difluoro (oxalato) phosphate, lithium tetrafluoroborate, lithium tetrafluorooxalato phosphate, lithium bis (trifluoromethylsulfonyl) imide, lithium bis (fluorosulfonyl) imide, and lithium tetrafluoromalonato phosphate.

4. The nonaqueous electrolyte solution of claim 2, wherein the lithium salt is present in the nonaqueous electrolyte solution in an amount of 10 to 20% by mass.

5. The nonaqueous electrolytic solution of claim 2, wherein the nonaqueous organic solvent is at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, butyl acetate, γ -butyrolactone, propyl propionate, ethyl propionate, and ethyl butyrate.

6. The nonaqueous electrolyte solution of claim 2, wherein the nonaqueous organic solvent is contained in the nonaqueous electrolyte solution in an amount of 60 to 80% by mass.

7. The nonaqueous electrolytic solution of claim 2, further comprising an auxiliary, the auxiliary agent is at least one of 2,2, 2-trifluoroethyl carbonate, 2,2, 2-trifluoropropyl carbonate, vinylene carbonate, fluoroethylene carbonate, ethylene difluorocarbonate, diethyl pyrocarbonate, 1, 3-propane sultone, vinyl sulfate, tris (trimethylsilane) phosphate, tris (trimethylsilane) phosphite, 4 '-bi-1, 3-dioxolane-2, 2' -dione, 3-divinyl disulfate, triallyl phosphate, succinonitrile, adiponitrile, 1,3, 6-hexanetrinitrile and 1, 2-bis (cyanoethoxy) ethane.

8. The nonaqueous electrolyte solution of claim 7, wherein the auxiliary is present in the nonaqueous electrolyte solution in an amount of 2 to 10.5% by mass.

9. A lithium ion battery comprising a positive electrode material and a negative electrode material, further comprising the nonaqueous electrolytic solution according to any one of claims 2 to 8, and having a maximum charging voltage of 4.53V.

10. The lithium ion battery of claim 9, wherein the positive electrode material is lithium cobaltate.