CN110048164B - Soft package lithium ion silicon carbon battery electrolyte and lithium ion battery - Google Patents

Soft package lithium ion silicon carbon battery electrolyte and lithium ion battery Download PDF

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CN110048164B
CN110048164B CN201910409950.2A CN201910409950A CN110048164B CN 110048164 B CN110048164 B CN 110048164B CN 201910409950 A CN201910409950 A CN 201910409950A CN 110048164 B CN110048164 B CN 110048164B
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electrolyte
additive
battery
lithium
carbonate
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CN110048164A (en
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高学友
朱坤庆
夏小勇
庞佩佩
计阳
聂灿
陶德瑜
刘露
陈伟峰
楚英
张涛
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Dongguan Weike Battery Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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Abstract

The invention provides a soft package lithium ion silicon carbon battery electrolyte and a lithium ion battery, wherein the electrolyte comprises an additive A and an additive B, the structure of the additive A is shown as a formula I, and the structure of the additive B is shown as a formula II. The electrolyte can form a protective film on the positive electrode and the negative electrode, so that the better high-pressure resistance of the positive electrode and the negative electrode of the battery is improved, the expansion rate of the silicon-carbon negative electrode is reduced, the side reaction loss of the electrolyte is effectively reduced, the cycle life and the high-temperature storage performance of the battery are improved, and the low-temperature charging and discharging performance of the battery is not influenced.

Description

Soft package lithium ion silicon carbon battery electrolyte and lithium ion battery
Technical Field
The invention belongs to the field of lithium ion batteries, relates to an electrolyte, and particularly relates to a soft package lithium ion silicon carbon battery electrolyte and a lithium ion battery.
Background
In recent years, the demand of electronic products on lithium ion batteries is continuously increased, the lithium ion batteries are rapidly developed, the requirement on high energy density of the batteries is also continuously improved, high-voltage lithium cobaltate materials and the like are applied, the voltage of the batteries is continuously improved, and is improved from original 4.2V to 4.4V, 4.43V, 4.45V and 4.48V, and the possibility of continuous improvement is provided in the future. The improvement of the energy density inevitably brings about the reduction of the high-temperature storage performance and the cycle life of the battery, and the problems of the compatibility of the electrolyte caused by the high compaction density of the material and the silicon carbonization of the cathode. It is necessary to design a novel soft-packaged high-energy-density lithium ion battery brick surface negative electrode electrolyte to meet the requirements of consumers. The electrolyte is added with two newly screened combined additives to mutually assist, so that the high-temperature storage and long cycle life of the soft-package high-energy-density lithium ion silicon carbon negative electrode battery can be met, and the low-temperature charging and discharging performance of the battery is not influenced.
Disclosure of Invention
In order to solve the technical problems in the prior art, the invention provides the soft-package lithium ion silicon carbon battery electrolyte and the lithium ion battery, wherein the electrolyte can form protective films on the positive electrode and the negative electrode of the battery, so that the positive electrode and the negative electrode of the battery have better high-pressure resistance, the expansion rate of the silicon carbon negative electrode is reduced, the side reaction loss of the electrolyte is effectively reduced, and the cycle life and the high-temperature storage performance of the battery are improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
one purpose of the invention is to provide soft package lithium ion silicon carbon battery electrolyte, wherein the electrolyte comprises an additive A and an additive B, the structure of the additive A is shown in a formula I, and the structure of the additive B is shown in a formula II:
Figure GDA0003132705500000021
wherein R is1、R2And R3Each independently is a substituted or unsubstituted alkyl group of C1-C5 or
Figure GDA0003132705500000022
Figure GDA0003132705500000023
Any one of (1), R4、R5And R6Each independently is a substituted or unsubstituted alkyl group of C1-C5, n1And n2Each independently an integer from 1 to 3, such as 1,2, and 3.
As a preferred embodiment of the present invention, the electrolyte includes a lithium salt, an organic solvent, an additive a, and an additive B.
In a preferred embodiment of the present invention, the total amount of the additive a and the additive B is 0.5 to 5% by mass of the total electrolyte, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5% by mass, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.
Preferably, the mass ratio of the additive A to the additive B is 1: 2.
In the invention, the additive B has the function of forming a film on the surface of the anode to cover the active site of the anode, the metal ions are prevented from dissolving out through the complexation of the cyano groups and the metal ions, the effect of protecting the anode is achieved, and the cyano groups can complex free heavy metal ions to prevent the heavy metal ions from being separated out on the cathode. When the amount of the additive B added is more than 1.5% by mass based on the total mass of the electrolyte, the resistance of the battery starts to increase and the compatibility of the electrolyte with the silicon-based material is also poor due to the thick film formed by the additive B. According to the electrochemical reaction of a silicon-carbon cathode interface, organic functional groups are more easily introduced into the Si-H surface, a structure containing ethoxy groups is introduced by combining the additive A in the additive to form a Si-OCmHn interface intermediate phase, and the electrolyte is more easily compatible with commercial silicon-based materials to form a stable SEI film. The matching use of the two combined additives effectively prevents the defect of high impedance when the single additive is used in high amount. But also effectively prevents the effect of improving high temperature and circulation caused by the small dosage of a single additive.
In a preferred embodiment of the present invention, the organic solvent accounts for 65 to 75% of the total mass of the electrolyte, such as 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, or 75%, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.
Preferably, the lithium salt accounts for 13-17% of the total mass of the electrolyte, such as 13%, 14%, 15%, 16%, or 17%, but not limited to the recited values, and other values not recited in the range of the values are also applicable.
As a preferred embodiment of the present invention, the organic solvent includes any one or a combination of at least two of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, γ -butyrolactone, propyl propionate, ethyl 2,2, 2-trifluoroethyl carbonate, diethyl 2,2, 2-trifluorophosphate, or ethyl 2,2, 2-trifluorophosphate, and typical but non-limiting examples of the combination are: a combination of ethylene carbonate and dimethyl carbonate, a combination of dimethyl carbonate and diethyl carbonate, a combination of diethyl carbonate and ethyl methyl carbonate, a combination of ethyl methyl carbonate and propylene carbonate, a combination of propylene carbonate and γ -butyrolactone, a combination of γ -butyrolactone and propyl propionate, a combination of propyl propionate and ethyl propionate, a combination of ethyl propionate and 2,2, 2-trifluoroethyl carbonate, a combination of 2,2, 2-trifluoroethyl carbonate and 2,2, 2-trifluoropropyl carbonate, or a combination of ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, etc.
As a preferred embodiment of the present invention, the lithium salt includes a mixture of lithium hexafluorophosphate and any one or a combination of at least two of lithium bis (oxalato) borate, lithium difluoro (oxalato) phosphate, lithium tetrafluorooxalato phosphate, lithium bis (trifluoromethylsulfonyl) imide, lithium bis (fluorosulfonato) imide or lithium difluoro (malonato) phosphate, and typical but non-limiting examples of the combination are: a combination of lithium bis (oxalato) borate and lithium difluoro (oxalato) borate, a combination of lithium difluoro (oxalato) borate and lithium difluoro (oxalato) phosphate, a combination of lithium difluoro (oxalato) phosphate and lithium tetrafluoro (oxalato) phosphate, a combination of lithium tetrafluoro (oxalato) phosphate and lithium bis (trifluoromethylsulfonyl) imide, a combination of lithium bis (trifluoromethylsulfonyl) imide and lithium bis (fluorosulfonato) imide, a combination of lithium bis (fluorosulfonato) imide and lithium difluoromalonic acid phosphate, a combination of lithium difluorobis (malonato) phosphate and lithium bis (oxalato) borate, a combination of lithium difluoro (oxalato) borate and lithium difluorooxalato phosphate, and the like.
As a preferred embodiment of the present invention, the electrolyte solution includes an auxiliary agent, and the auxiliary agent includes any one or a combination of at least two of vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate, ethylene carbonate, 1, 3-propene sultone, 1, 4-butane sultone, 1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, ethylene glycol dipropionitrile ether, tris (2,2, 2-trifluoroethyl) phosphite, 1,3,6-hexane trinitrile, citric anhydride, perfluoroglutaric anhydride, fluorobenzene, 2-fluorobiphenyl, boron trifluoride tetrahydrofuran, tris (trimethylsilane) phosphate, cyclic phosphoric anhydride, and vinyl sulfate, and the combination is typically but not limited to: a combination of vinylene carbonate and 1,3-propane sultone, a combination of 1,3-propane sultone and fluoroethylene carbonate, a combination of fluoroethylene carbonate and vinylethylene carbonate, a combination of vinylethylene carbonate and 1, 3-propene sultone, a combination of 1, 3-propene sultone and 1, 4-butane sultone, a combination of 1, 4-butane sultone and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, a combination of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and ethylene glycol dipropionin ether, a combination of ethylene glycol dipropionin ether and tris (2,2, 2-trifluoroethyl) phosphite, tris (2,2, 2-trifluoroethyl) phosphite and 1, a combination of 3,6-hexanetricarbonitrile, a combination of 1,3,6-hexanetricarbonitrile and citric anhydride, a combination of citric anhydride and perfluoroglutaric anhydride, a combination of perfluoroglutaric anhydride and fluorobenzene, a combination of fluorobenzene and 2-fluorobiphenyl, a combination of 2-fluorobiphenyl and boron trifluoride tetrahydrofuran, a combination of boron trifluoride tetrahydrofuran and tris (trimethylsilane) phosphate, a combination of tris (trimethylsilane) phosphate and cyclic phosphoric anhydride, a combination of cyclic phosphoric anhydride and vinyl sulfate, or 1,3-propanesultone, fluoroethylene carbonate, 1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, a combination of 1,3,6-hexanetricarbonitrile, a combination of cyclic phosphoric anhydride and vinyl sulfate, and the like.
In the invention, when the vinyl sulfate in the auxiliary agent is added into the electrolyte, the surface SEI film component can be modified, the relative content of S and O is improved, S and O contain lone pair electrons, lithium ions can be attracted, shuttle of the lithium ions in the SEI film is accelerated, and the interface impedance of the battery is reduced, so that the low-temperature charge and discharge performance of the high-voltage lithium ion battery is effectively improved. The low-temperature charge and discharge performance influence factors of the lithium ion battery comprise the reduction of the conductivity of the electrolyte, the decomposition of the electrolyte to generate a new SEI film due to the deposition of metal lithium in the charging process, and the reduction of the diffusion speed of lithium ions in the negative electrode. At low temperature, the capacity of the lithium ion battery is greatly attenuated, and after low-temperature circulation, the lithium ion battery is placed at room temperature again, and the capacity of the lithium ion battery cannot be recovered to the capacity at room temperature. The impedance of the battery is increased, the polarization is enhanced, lithium metal deposition occurs on the negative electrode in the charging process, the deposited lithium and the electrolyte undergo a reduction reaction, and a new SEI film is formed to be covered on the original SEI film. Therefore, the impedance of the battery is effectively reduced, the polarization of the battery during low-temperature charging is reduced, and lithium metal deposition is prevented by matching the two combined additives.
In the invention, 1,3,6-hexanetricarbonitrile used as a high-voltage positive electrode additive has good thermal stability, high oxidation stability and low nitrile group (-C ≡ N) in flammability, and can be combined with metal ions with electropositivity on the surface of a positive electrode material to participate in the formation of an electrode surface film due to strong electronegativity, and meanwhile, nitrile groups in the film can provide an environment favorable for penetration of lithium ions, so that the decomposition of an electrolyte can be inhibited, and the cycle stability of the high-voltage positive electrode material can be improved; tris (2,2, 2-trifluoroethyl) borate (TTFEB) is used as a novel boron-based anion receptor, which can not only inhibit the decomposition of an electrolyte and the dissolution of a transition metal by capturing an F anion in the electrolyte through an internal B atom, but also enable the electrolyte to have higher oxidation stability because the F contained in the electrolyte is an electron donating group.
In the present invention, the auxiliary agent is preferably 1,3-Propane Sultone (PS) and Fluoroethylene carbonate (FEC), 1,2,2-Tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), 1,3,6-Hexanetricarbonitrile (1,3,6-Hexanetricarbonitrile), cyclic phosphoric anhydride, vinyl sulfate (DTD). Wherein the FEC has a lower LUMO (orbital with lowest unoccupied electron energy level is called lowest unoccupied orbital, represented by LUMO) value than the solvent, and is capable of being preferentially dissolved in the solvent to perform a reduction reaction at the negative electrode, thereby forming a stable and flexible SEI film. The PS as an additive has good film-forming property and low-temperature conductivity, can inhibit the decomposition of FEC, and improves the capacity loss of the lithium ion battery during the first charge and discharge, thereby being beneficial to improving the reversible capacity of the lithium ion battery and further improving the long-term cycle performance of the lithium ion battery. Furthermore, the addition amounts of the FEC, the PS, the HFC, the 1,3,6-hexanetricarbonitrile, the cyclic phosphoric anhydride and the DTD correspond to 3-5%, 0.5-3.0%, 0.2-1.0%, 0.2-0.5% and 0.5-1.0% of the total mass of the electrolyte.
In a preferred embodiment of the present invention, the additive accounts for 5 to 18% of the total mass of the electrolyte, such as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, or 18%, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.
The invention also aims to provide a soft package lithium ion silicon carbon battery, which comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, wherein the diaphragm is arranged between the positive electrode and the negative electrode, and the electrolyte is any one of the above electrolytes.
As a preferable technical scheme of the invention, the active material of the positive electrode is LiNixCoyMnzM1-x-y-zO2Or LiNixCoyAlzM1-x-y-zO2Wherein M is any one of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti, y is more than or equal to 0 and less than or equal to 1, x is more than or equal to 0 and less than 1, z is more than or equal to 0 and less than or equal to 1, and x + y + z is less than or equal to 1; the active material of the negative electrode is a composite negative electrode material of silicon carbon or silicon monoxide and artificial graphite.
In the present invention, the separator is generally a polyolefin porous film having a porous structure and capable of resisting a non-aqueous organic solvent, such as a polyolefin microporous film of polyethylene (prepared by a wet process), polypropylene (prepared by a dry process), and the like.
Compared with the prior art, the invention has at least the following beneficial effects:
the invention provides a soft package lithium ion silicon carbon battery electrolyte and a lithium ion battery, wherein the highest charging voltage of the battery is 4.4V-4.48V, the electrolyte forms a protective film on a positive electrode and a negative electrode, the protective film has better high pressure resistance and expansion inhibition on a silicon carbon negative electrode, the side reaction loss of the electrolyte is effectively reduced, the cycle life and the high-temperature storage performance of the battery are improved, the compatibility of the electrolyte and a silicon-based material is improved, the impedance of the battery is effectively reduced, the polarization and the low-temperature charge-discharge performance of the battery during low-temperature charging are reduced, and lithium metal deposition is prevented.
Detailed Description
For the purpose of facilitating an understanding of the present invention, the present invention will now be described by way of examples. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
Example 1
The embodiment provides a soft package lithium ion silicon carbon battery, and a preparation method thereof is as follows:
(1) preparing a positive electrode: high-voltage positive electrode active material high-voltage 4.43V lithium cobaltate (LiCoO2) (purchased from mansion tungsten new energy), CNTs (carbon nanotubes) and PVDF (polyvinylidene fluoride) were mixed in a mass ratio of 98.2: 0.8: 1.0, uniformly mixing, and then dispersing in N-methyl-2-pyrrolidone to obtain anode slurry; and uniformly coating the anode slurry on two sides of the aluminum foil, rolling and cutting to obtain an anode plate, and finally baking and vacuum drying for later use.
(2) Preparing a negative electrode: silicon-carbon T3C-500 negative electrode material (from an Aimin new material), acetylene black, CMC (carboxymethyl cellulose), LA136D adhesive (Yindile) according to the mass ratio of 97.0: 1.0: 0.5: 1.5, uniformly mixing, and then dispersing in deionized water to obtain cathode slurry; and uniformly coating the negative electrode slurry on two surfaces of the copper foil, rolling and cutting to obtain a negative electrode plate, and finally baking and vacuum drying for later use.
(3) Preparing electrolyte: in a nitrogen-filled glove box (O)2＜2ppm，H2O is less than 3ppm), uniformly mixing ethylene carbonate, propylene carbonate, propyl propionate and diethyl carbonate according to the mass ratio of 2:2:1:5 to prepare an organic solvent; then taking an organic solvent accounting for 70 percent of the total mass of the electrolyte, adding FEC accounting for 5 percent of the total mass of the electrolyte, PS accounting for 3 percent of the total mass of the electrolyte, 1 percent of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether accounting for 3 percent of the total mass of the electrolyte and the like1,3,6-hexanetricarbonitrile, 0.5% of cyclic phosphoric anhydride, 1% of DTD, 0.5% of additive A (ethyl dipropargyl phosphate) and 1% of additive B (1, 4-dicyano-2-butene) to obtain a mixed solution; and slowly adding the mixture of lithium hexafluorophosphate and lithium difluorooxalate phosphate into the mixed solution to prepare 1.2mol/L lithium salt solution, and uniformly mixing to obtain the electrolyte.
(4) Preparing a lithium ion battery: and (3) arranging and winding the positive plate, the diaphragm (a polyolefin porous membrane purchased from Asahi chemical technology) and the negative plate in sequence to obtain a naked battery cell, and carrying out aluminum plastic membrane packaging, re-baking, liquid injection, standing, formation, clamp shaping, secondary sealing and capacity testing to finish the preparation of the lithium ion soft package battery.
Example 2
This example provides a soft-packed lithium-ion silicon-carbon battery, which is prepared under the same conditions as example 1 except that the organic solvent accounts for 66.5% of the total mass of the electrolyte, and the additive a and the additive B account for 1% and 4% of the total mass of the electrolyte, respectively.
Example 3
This example provides a soft-packed lithium-ion silicon-carbon battery except that the addition of A is replaced by
Figure GDA0003132705500000081
Otherwise, the conditions were the same as in example 1.
Example 4
This example provides a soft-packed lithium-ion silicon-carbon battery except that the addition of A is replaced by
Figure GDA0003132705500000082
Otherwise, the conditions were the same as in example 1.
Example 5
This example provides a soft-packed lithium-ion silicon-carbon battery except that the addition of A is replaced by
Figure GDA0003132705500000091
Otherwise, the conditions were the same as in example 1.
Example 6
This example provides a soft-packed lithium-ion silicon-carbon battery except that the addition of A is replaced by
Figure GDA0003132705500000092
Otherwise, the conditions were the same as in example 1.
Example 7
This example provides a soft-packed lithium-ion silicon-carbon battery except that the addition of A is replaced by
Figure GDA0003132705500000093
Replacement of additive B by
Figure GDA0003132705500000094
Otherwise, the conditions were the same as in example 1.
Example 8
This example provides a soft-packed lithium-ion silicon-carbon battery except that the addition of A is replaced by
Figure GDA0003132705500000095
Replacement of additive B by
Figure GDA0003132705500000096
Otherwise, the conditions were the same as in example 1.
Comparative examples 1,2 and 3
The preparation method of the lithium ion battery is the same as that of the example 1, except that in the step (3), the nonaqueous organic solvent accounting for 71.5%, 71% and 67.5% of the total mass of the electrolyte is taken according to the proportion of the solvent in the example 1, the components and the addition amount of the additive are unchanged (except for two combined additives), and the percentage (wt%) of A, B of the two combined additives accounting for the total mass of the electrolyte is shown in table 1.
TABLE 1
Figure GDA0003132705500000101
The lithium ion batteries prepared in examples 1 to 8 and comparative examples 1 to 3 were tested for their respective relevant properties, including normal temperature cycle performance, high temperature storage thickness expansion, low temperature cycle lithium precipitation observation, and hot-punching test, and the specific test methods were as follows:
(1) and (3) testing the normal-temperature cycle performance: the battery after formation was charged to 4.43V (0.01C as a cutoff current) at 25 ℃ with a constant current and a constant voltage of 0.5C, and then discharged to 3.0V with a constant current of 0.5C, and the retention of the cycle capacity at 500 cycles of charge/discharge was calculated as follows:
capacity retention (%) at 500 cycles: (500 cycles discharge capacity/1 st cycle discharge capacity × 100%)
(2) And (3) testing the high-temperature storage performance: the thickness of the formed battery is tested, the battery is charged to 4.43V (the cut-off current is 0.01C) by using a constant current and a constant voltage of 0.5C at 25 ℃, then the battery is stored for 6H at the high temperature of 85 ℃, after the high-temperature storage is finished, the thickness of the battery core or the battery is measured in an oven, and the increase rate of the thickness of the battery before and after the high-temperature storage is calculated, wherein the calculation formula is as follows:
cell thickness increase (%) which is (cell thickness after high temperature-cell thickness before high temperature)/cell thickness before high temperature × 100%
(3) And (3) testing thermal shock performance: charging to 4.43V (cutoff current is 0.01C) at constant current and constant voltage of 0.5C in an environment of 25 ℃, putting the battery cell or the battery into an oven, heating the battery cell or the battery to 150 +/-2 ℃ at the speed of 5 +/-2 ℃/min, and keeping for 10 minutes after the temperature of the oven reaches 150 +/-2 ℃. The battery was observed not to ignite and not to explode as a pass test.
(4) And (3) observing lithium precipitation of the negative plate: charging to 4.43V (cutoff current of 0.01C) at 0 deg.C under constant current and constant voltage of 0.3C, discharging to 3.0V with constant current of 0.5C, and dissecting slight lithium precipitation according to the charge-discharge cycle
The results of the performance tests of the lithium ion batteries prepared in examples 1 to 8 and comparative examples 1 to 3 are shown in table 2.
TABLE 2
Figure GDA0003132705500000111
Figure GDA0003132705500000121
From the above tests, it can be seen that the combined additive has a significant improvement in the cycle of the high-voltage battery and a significant inhibition effect on the expansion of the high-temperature storage battery in examples 1 and 3 to 8. The thermal shock is passed, and the lithium is not separated out after low-temperature cycling.
The amount of the two combined additives is increased in example 2, which can be seen to be helpful for high-temperature storage of the battery, but the dosage of the B additive is increased, so that the film formation is thicker, the battery impedance is increased, the cycle is not further promoted, the influence is caused on the cycle, and lithium is precipitated by low-temperature charging and discharging.
Comparative example 2 it can be seen that the combination additive a is helpful for battery cycling, slightly helpful for high temperature storage, and no lithium evolution at low temperature.
Comparative example 3 shows that the combined additive B is helpful to high temperature, has no obvious help to circulation, has lithium precipitation phenomenon at low temperature, increases resistance when a single additive B is used, and has poor low-temperature effect.
The combined additives A and B are helpful for thermal shock testing of the battery, and proper addition of the combined additives is beneficial to improving the cycle life and the high-temperature storage performance of the battery. Through the combined use of the two combined additives A and B and the auxiliary action of common additives such as vinyl sulfate (DTD) and the like, the cycle life requirement of a high-voltage high-energy-density battery can be met, the high-temperature storage performance of the battery is improved, the low-temperature impedance rise of the battery can be effectively controlled, the low-temperature charge and discharge performance is improved, and the low-temperature lithium precipitation phenomenon is prevented.
The applicant states that the present invention is illustrated by the above examples to show the detailed process equipment and process flow of the present invention, but the present invention is not limited to the above detailed process equipment and process flow, i.e. it does not mean that the present invention must rely on the above detailed process equipment and process flow to be implemented. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims (12)

1. The utility model provides a soft packet of lithium ion silicon carbon battery electrolyte, its characterized in that, electrolyte includes additive A and additive B, additive A's structure is shown as formula I, additive B's structure is shown as formula II:
Figure FDA0003457906160000011
wherein n is1And n2Each independently is an integer of 1 to 3;
R1is selected from
Figure FDA0003457906160000012
R2Is selected from
Figure FDA0003457906160000013
R3Is selected from
Figure FDA0003457906160000014
Or R1Is selected from
Figure FDA0003457906160000015
R2Is selected from
Figure FDA0003457906160000016
R3Is selected from
Figure FDA0003457906160000017
Or R1Is selected from
Figure FDA0003457906160000018
R2Is selected from
Figure FDA0003457906160000019
R3Is selected from
Figure FDA00034579061600000110
Or R1Is selected from
Figure FDA00034579061600000111
R2Is selected from
Figure FDA00034579061600000112
R3Is selected from
Figure FDA00034579061600000113
2. The electrolyte of claim 1, wherein the electrolyte comprises a lithium salt, an organic solvent, an additive a, and an additive B.
3. The electrolyte according to claim 1, wherein the total amount of the additive A and the additive B is 0.5-5% of the total mass of the electrolyte.
4. The electrolyte of claim 3, wherein the additive A and the additive B are present in a mass ratio of 1: 2.
5. The electrolyte of claim 2, wherein the organic solvent is 65-75% of the total mass of the electrolyte.
6. The electrolyte of claim 2, wherein the lithium salt is present in an amount of 13 to 17% by weight of the total electrolyte.
7. The electrolyte of claim 2, wherein the organic solvent comprises any one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, γ -butyrolactone, propyl propionate, ethyl 2,2, 2-trifluoromethane carbonate, diethyl 2,2, 2-trifluorocarbonate, or ethyl 2,2, 2-trifluoropropyl carbonate, or a combination of at least two thereof.
8. The electrolyte of claim 2, wherein the lithium salt comprises a mixture of lithium hexafluorophosphate and any one or a combination of at least two of lithium bis (oxalato) borate, lithium difluoro (oxalato) phosphate, lithium tetrafluorooxalato phosphate, lithium bis (trifluoromethylsulfonyl) imide, lithium bis (fluorosulfonato) imide, or lithium difluoro (malonato) phosphate.
9. The electrolyte according to claim 1, wherein the electrolyte comprises an auxiliary agent, and the auxiliary agent comprises any one or a combination of at least two of vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate, ethylene carbonate, 1, 3-propene sultone, 1, 4-butane sultone, 1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, ethylene glycol dipropionitrile ether, tris (2,2, 2-trifluoroethyl) phosphite, 1,3,6-hexanetricarbonitrile, citric anhydride, perfluoroglutaric anhydride, fluorobenzene, 2-fluorobiphenyl, boron trifluoride tetrahydrofuran, tris (trimethylsilane) phosphate, cyclic phosphoric anhydride, or vinyl sulfate.
10. The electrolyte of claim 9, wherein the additive comprises 5-18% of the total mass of the electrolyte.
11. A soft package lithium ion silicon carbon battery, which is characterized in that the battery comprises a positive electrode, a negative electrode, a diaphragm arranged between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is the electrolyte in any one of claims 1-10.
12. The battery of claim 11, wherein the battery is characterized byCharacterized in that the active material of the positive electrode is LiNixCoyMnzM1-x-y-zO2Or LiNixCoyAlzM1-x-y-zO2Wherein M is any one of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti, y is more than or equal to 0 and less than or equal to 1, x is more than or equal to 0 and less than 1, z is more than or equal to 0 and less than or equal to 1, and x + y + z is less than or equal to 1; the active material of the negative electrode is silicon carbon.
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