Electrolyte and lithium ion battery

Abstract

The application relates to battery technology and discloses an electrolyte and a lithium ion battery. The electrolyte comprises an electrolyte salt, an organic solvent and an additive. The additive comprises an additive A, an additive B and an additive C. The additive A is of a general structure formula I: wherein R1-R3 are selected from any one of a hydrogen atom, a fluorine atom, an alkyl group and a substitution thereof, an alkenyl group and a substitution thereof; the additive B is of any one of a structure formula II, a structure formula III and a structure formula IV: wherein X1, X2, X3 and X4 are selected from any one of an alkyl group, a fluorine atom, a hydrogen atom, a halogenated alkyl group, an alkene, an alkyne group, an aromatic hydrocarbon group, a halogenated aromatic hydrocarbon group and an alkoxy group; and the additive C is at least two of vinylene carbonate, 1,3-propane sulfonic acid lactone, fluorinated vinyl carbonate, vinyl sulfate, butanedinitrile, hexanedinitrile, 1,3,6-hexane trinitrile, propylene sulfonic acid lactone, methane dimesylate, ethylene glycol bispropionitrile ether and a fluorine-containing ether.

Description

TECHNICAL FIELD

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

[0002] Due to the advantages of high specific energy, no memory effect, long cycle life, small self-discharge and the like, lithium ion batteries are widely used in digital, energy storage, electric vehicles and the like. In recent years, with the increasing demand for mobile office, higher requirements are put forward for the application environment of lithium ion batteries, such as notebook battery, which requires higher high-temperature storage and low-temperature discharge performance and longer nesting cycle life.

[0003] At present, while improving high-temperature storage or nesting cycle by adding additives, the low-temperature performance is often deteriorated, which cannot guarantee the low-temperature performance of the lithium ion battery. SUMMARY

[0004] The purpose of the present application is to provide an electrolyte and a lithium ion battery, which can improve the cell standing cycle, high-temperature storage and safety performance without deteriorating the low-temperature performance.

[0005] The present application discloses an electrolyte, comprising an electrolyte salt, an organic solvent and an additive, wherein the additive comprises an additive A, an additive B and an additive C.

[0006] The additive A is a general formula I as follows:

[0007]

[0008] wherein R1-R3 are selected from any one of hydrogen atom, fluorine atom, alkyl and its substitutes, alkenyl and its substitutes;

[0009] The additive B is any one of the following general formula II, formula III and formula IV:

[0010]

[0011] wherein X1, X2, X3, X4 are selected from any one of alkyl, fluorine atom, hydrogen atom, halogenated alkyl, alkene, alkyne group, aromatic hydrocarbon group, halogenated aromatic hydrocarbon group, alkoxy;

[0012] The additive C is at least two of vinylene carbonate, 1,3-propane sulfone lactone, fluorinated ethylene carbonate, vinyl sulfate, butanedinitrile, hexanedinitrile, 1,3,6-hexane trinitrile, propylene sulfone lactone, methane disulfide methylene ester, ethylene glycol bis(propionitrile) ether, fluorine-containing ether;

[0013] The mass percentage of the additive A in the electrolyte is 0.01% to 2%, the mass percentage of the additive B in the electrolyte is 0.01% to 2%, and the mass percentage of the additive C in the electrolyte is 7% to 20%.

[0014] Optionally, the mass percentage of the additive A in the electrolyte is 0.5% to 1.5%.

[0015] Optionally, the mass percentage of the additive B in the electrolyte is 0.3% to 0.7%.

[0016] Optionally, the mass percentage of the additive C in the electrolyte is 10% to 15%.

[0017] Optionally, the additive A is allyl isocyanurate, and the mass percentage of the allyl isocyanurate in the electrolyte is 1%.

[0018] Optionally, the additive B is any one of difluoroborane-based difluoroborane, lithium tetrafluoroborate or fluorodimethoxyborane, and the mass percentage of the difluoroborane-based difluoroborane, lithium tetrafluoroborate or fluorodimethoxyborane in the electrolyte is 0.5%.

[0019] Optionally, the electrolyte salt is lithium salt, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, lithium difluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, the organic solvent is a mixture of ethylene carbonate, propylene carbonate, diethyl carbonate and propyl propionate, and the concentration of the lithium salt in the electrolyte is 0.9 mol / L to 2 mol / L.

[0020] Optionally, the concentration of the lithium salt in the electrolyte is 1.0 mol / L to 1.3 mol / L.

[0021] Optionally, the total content of boron in the additive B accounts for >200 ppm in the mass of the electrolyte.

[0022] The application further discloses a lithium ion battery comprising the electrolyte.

[0023] The electrolyte of the present application, by adding the additive A (containing a triazine ring structure), has a structural property of being active, can be preferentially oxidized on the positive electrode surface, and at the same time, the unsaturated hydrocarbon material can undergo chain-opening polymerization, forming a film with characteristics such as denseness, solvent resistance, etc., reducing the reactivity of the electrode surface, reducing the oxidative decomposition of the electrolyte at high temperatures, and at the same time, by adding the additive B, the boron compound can participate in the formation of the SEI film at the negative electrode, the formed SEI film is rich in B-O, B-F bonds with stronger mechanical properties and better toughness, which is beneficial to the passage of Li ions; at the same time, the B element can also inhibit the dissolution of metal ions at the positive electrode, and the additive C can be targeted to act on the positive and negative electrodes, mainly playing the roles of positive and negative electrode film formation and positive electrode complexation, under the cooperation of the additive A, the additive B and the additive C, the low-temperature performance can be improved without deterioration, the thermal stability and cycle performance of the battery can be improved, the battery life can be prolonged and the safety performance can be improved. DETAILED DESCRIPTION

[0024] It should be understood that the terms used herein, the specific structural and functional details disclosed, are only for the purpose of describing specific embodiments, and are representative, but the present application can be embodied in many alternative forms, and should not be interpreted as being limited to the embodiments described herein.

[0025] The present application will be described in detail below with reference to alternative embodiments.

[0026] As an embodiment of the present application, an electrolyte is disclosed, comprising an electrolyte salt, an organic solvent and an additive, the additive comprising an additive A, an additive B and an additive C;

[0027] The additive A is the following structural general formula I:

[0028]

[0029] Among them, R1~R3 are selected from any one of hydrogen atom, fluorine atom, alkyl and its substitutes, alkenyl and its substitutes;

[0030] The additive B is any one of the following structural general formula II, formula III and formula IV:

[0031]

[0032] Among them, X1, X2, X3, X4 are selected from any one of alkyl, fluorine atom, hydrogen atom, halogenated alkyl, alkene, alkyne group, aromatic hydrocarbon group, halogenated aromatic hydrocarbon group, alkoxy group;

[0033] The additive C is at least two of vinylene carbonate (VC), 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), succinonitrile (SN), adiponitrile (ADN), 1,3,6-hexanetrione (HTCN), propene sultone (PST), methanediyl dimethanesulfonate (MMDS), ethylene glycol bis(propionitrile) ether (EGBE), fluorine-containing ether (D2).

[0034] More specifically, the mass percentage of the additive A in the electrolyte is 0.01% to 2%, and the additive A can be 0.01%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%.

[0035] More specifically, the mass percentage of the additive B in the electrolyte is 0.01% to 2%, and the additive B can be 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%.

[0036] More specifically, the mass percentage of the additive C in the electrolyte is 7% to 20%, and the additive C can be 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%.

[0037] More specifically, the additive A is allyl isocyanurate, and the mass percentage of the allyl isocyanurate in the electrolyte is 1%.

[0038] More specifically, the additive B is any one of difluoroborane oxylate difluoroborane, lithium tetrafluoroborate, or fluorodimethoxyborane, and the mass percentage of the difluoroborane oxylate difluoroborane, lithium tetrafluoroborate, or fluorodimethoxyborane in the electrolyte is 0.5%.

[0039] More specifically, the electrolyte salt is a lithium salt, and the concentration of the lithium salt in the electrolyte is 0.9 mol / L to 2 mol / L. The concentration of the lithium salt can be 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L. In the embodiment, the lithium salt is limited in the range to prevent the electrolyte from having low conductivity due to low lithium salt concentration, affecting the cycle and rate performance of the battery, and prevent the electrolyte from having high viscosity due to high lithium salt concentration, also affecting the dynamics of the battery.

[0040] More specifically, the total content of boron in the additive B accounts for >200 ppm in the mass of the electrolyte. In the embodiment, the additive B is limited in the range to optimize the positive / negative electrode / electrolyte interface, reduce the surface activity of the positive electrode, improve the stability of the SEI film, and significantly improve the safety.

[0041] More specifically, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium difluoro(oxalato)borate (LiODFB), lithium difluorophosphate (LiPOF2), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium difluorophosphate (LiPOF2), and the organic solvent is a mixture of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP).

[0042] The electrolyte of the embodiment can be oxidized on the surface of the positive electrode by adding the additive A (containing a triazine ring structure) which has active structural properties, and the unsaturated hydrocarbon material can be open-chain polymerized to form a film with the characteristics of compactness and solvent resistance, thereby reducing the reaction activity of the electrode surface and reducing the oxidative decomposition of the electrolyte at high temperature. In addition, by adding the additive B, the boron compound can participate in the formation of the SEI film at the negative electrode, and the formed SEI film is rich in B-O and B-F bonds with stronger mechanical properties and better toughness, which is beneficial to the passage of Li ions. In addition, the B element can also inhibit the dissolution of metal ions from the positive electrode. The additive C can be used for the positive and negative electrodes, mainly for the formation of the positive and negative electrodes and the complexation of the positive electrode. By using the additive A, the additive B, and the additive C together, the low-temperature performance can be improved without deterioration, the thermal stability and cycle performance of the battery can be improved, the service life of the battery can be prolonged, and the safety performance can be improved.

[0043] As another embodiment of the application, a lithium ion battery is disclosed, which includes the electrolyte as described above. The lithium ion battery further includes a positive electrode sheet, a negative electrode sheet, and a separator between the positive and negative electrode sheets.

[0044] The embodiment also discloses a preparation method of the lithium ion battery.

[0045] Preparation of the positive electrode sheet: the positive electrode active material lithium cobaltate (LiCoO2), the conductive agent CNT, and the binder PVDF are mixed in a weight ratio of 97:1.5:1.5 in the NMP solvent, and the slurry is coated on the positive electrode current collector Al foil, and then subjected to the processes of drying, cold pressing, slitting, sheet making, welding of the tabs, and gluing, to obtain the positive electrode sheet meeting the winding requirements.

[0046] Preparation of the negative electrode sheet: the negative electrode active material graphite negative electrode, the conductive agent SP, the thickening agent CMC, and the binder SBR are mixed in a mass ratio of 96.3:1:1.2:1.5 in the corresponding deionized water solvent, and the mixture is fully stirred to form a uniform negative electrode slurry. The slurry is coated on the negative electrode current collector Cu foil, and then subjected to the processes of drying, cold pressing, slitting, sheet making, welding of the tabs, and gluing, to obtain the negative electrode sheet meeting the winding requirements.

[0047] The electrolyte solution is prepared as follows:

[0048] The preparation steps of the electrolyte solution are as follows: ethylene carbonate (EC) / PC (polycarbonate) / DEC (diethyl carbonate) / propyl propionate (PP) are mixed in a mass ratio of 1:1:1:2 as the organic solvent; after being uniformly mixed, 1.2 mol / L lithium hexafluorophosphate (LiPF6) is slowly added to obtain a mixed solution with a LiPF6 concentration of 1.2 mol / L; after the lithium hexafluorophosphate (LiPF6) is completely dissolved, the corresponding contents of the additive A, the additive B, and the additive C are added, and the electrolyte solution is obtained.

[0049] The additive A is allyl isocyanurate, and its structural formula is as follows:

[0050]

[0051] The additive B is any one of difluoroborane-based difluoroborane, lithium tetrafluoroborate, or fluorodimethoxyborane, wherein the structural formula of the difluoroborane-based difluoroborane is as follows:

[0052]

[0053] The structural formula of the lithium tetrafluoroborate is as follows:

[0054]

[0055] The structural formula of the fluorodimethoxyborane is as follows:

[0056]

[0057] Embodiment:

[0058] Take 650 roasted liquid injection cell (moisture < 120 ppm), 14 groups of 50 cells, respectively, injection of electrolyte of Example 1~7 and Comparative Example 1~6 corresponding component content. Then according to the normal process of standing, formation, two seal, detection.

[0059] Example 1~7 and Comparative Example 1~6: all are a kind of high pressure system electrolyte, mainly composed of lithium hexafluorophosphate and solvent. Take 650 roasted liquid injection cell (moisture < 120 ppm), 13 groups of 50 cells, respectively, injection of electrolyte of Example 1~7 and Comparative Example 1~6. Then according to the normal process of standing, formation, two seal, detection.

[0060] Lithium ion battery performance test by the following 4 aspects:

[0061] 45℃ static cycle 50 weeks energy retention rate test: at 45℃, 0.7C constant current constant voltage charging to the upper limit voltage, cutoff current 0.05C, static 24h, 0.5C discharge to 3.0V, record the initial discharge energy E0, repeat 50 weeks, get the capacity E50 of 50 weeks cycle, then energy retention rate = E50 / E0.

[0062] 85℃ 6h storage thickness expansion rate test: at 25℃, 0.7C constant current constant voltage charging to the upper limit voltage, cutoff current 0.05C, 10min, test cell thickness H0, then in 85±2℃ storage 6h, thermal thickness H6, thickness expansion rate = (H6-H0) / H0.

[0063] -10℃ discharge 3.4V capacity retention rate test: at 25℃, 0.7C full, cutoff current 0.05C, static 10min, 25℃, 0.2C discharge to 3.0V, record the discharge capacity C0, 25℃, 0.7C full, cutoff current 0.05C, at-10℃, static 2H, then 0.2C discharge to 3.4V, record the discharge capacity C1, 3.4V capacity retention rate = C1 / C0.

[0064] 130℃ 30min thermal shock test: at 25℃ environment, discharge to 3.0V with given current 0.2C; 5min; 0.2C constant current constant voltage charging to the upper limit voltage, cutoff current 0.05C; 1h after measurement, voltage, internal resistance, the cell into the oven, monitor the surface temperature of the cell, oven temperature to 130±2℃ with 5±2℃ / min, and keep 30min after stop, judge standard cell no fire no explosion.

[0065] The additive composition added in the electrolyte of Example 1~7 and Comparative Example 1~6 is as follows:

[0066] Example Additive A Additive B Additive C Example 1 0.5％ 0.2％ 3% PS, 7% FEC, 2% AND, 1% HTCN Example 2 0.5％ 1％ 3% PS, 7% FEC, 2% AND, 1% HTCN Example 3 0.5％ 2％ 3% PS, 7% FEC, 2% AND, 1% HTCN Example 4 0.5％ 3％ 3% PS, 7% FEC, 2% AND, 1% HTCN Example 5 0.2％ 0.5％ 3% PS, 7% FEC, 2% AND, 1% HTCN Example 6 1％ 0.5％ 3% PS, 7% FEC, 2% AND, 1% HTCN Example 7 2％ 0.5％ 3% PS, 7% FEC, 2% AND, 1% HTCN Comparative Example 1 / / 3% PS, 7% FEC, 2% AND, 1% HTCN Comparative Example 2 / 0.5％ 3% PS, 7% FEC, 2% AND, 1% HTCN Comparative Example 3 0.5％ / 3% PS, 7% FEC, 2% AND, 1% HTCN Comparative Example 4 0.5％ 0.5％ 3% PS, 7% FEC, 2% AND, 1% HTCN Comparative Example 5 5％ / 3% PS, 7% FEC, 2% AND, 1% HTCN Comparative Example 6 / 5％ 3% PS, 7% FEC, 2% AND, 1% HTCN

[0067] The results of examples 1-7 and comparative examples 1-6 are as follows:

[0068]

[0069]

[0070] The test results of comparative examples 1-3 show that the addition of additive A or additive B improves the 45℃ standing cycle, 85℃ high-temperature storage and thermal shock performance of the battery cell;

[0071] The addition of additive A and additive B in comparative example 4 can significantly improve the 45℃ standing cycle, 85℃ high-temperature storage and safety performance;

[0072] In comparative examples 5-6, when the amount of additive A or additive B is 5%, the increase of additive A deteriorates the low-temperature discharge, and the high content of additive A leads to the increase of interface impedance and the discharge polarization, and the increase of additive B deteriorates the high-temperature storage, and the film-forming material of additive B is prone to decomposition reaction and gas production at 85℃ high temperature.

[0073] Comparative examples 1-7 and comparative example 1 show that the performance of additive A and additive B is improved first and then slightly deteriorated with the increase of the amount of additive A and additive B, and the comprehensive effect of comparative example 6 is the best, so the amount of additive A and additive B has a synergistic effect, which makes the film-forming have strong mechanical properties and toughness, and the film-forming impedance is in the corresponding range. By adding the corresponding amount of additive A and additive B, the low-temperature performance is not deteriorated, and the 45℃ standing cycle, 85℃ high-temperature storage and safety performance of the battery cell can be improved.

[0074] The above is a further detailed description of the present application in combination with specific optional embodiments, and the specific implementation of the present application should not be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, some simple deductions or substitutions can be made without departing from the concept of the present application, and all of them should be regarded as falling within the protection scope of the present application.

Claims

1. An electrolyte, characterized by, The electrolyte salt, organic solvent and additives, wherein the additives include additive A, additive B and additive C; The additive A is a general formula I: The general formula I R1~R3 are selected from hydrogen atom, fluorine atom, alkyl and its substitutes, alkenyl and its substitutes; The additive B is a general formula II and fluorine dimethoxy boron hydride: The general formula II X1, X2, X3, X4 are selected from alkyl, fluorine atom, hydrogen atom, halogenated alkyl, alkene, alkyne, aromatic hydrocarbon, halogenated aromatic hydrocarbon, alkoxy; The additive C is at least two of vinylene carbonate, 1,3-propane sulfonic acid lactone, fluorinated vinylene carbonate, vinyl sulfate, butanedinitrile, hexanedinitrile, 1,3,6-hexane trinitrile, propylene sulfonic acid lactone, methane dimesylate, ethylene glycol bispropionitrile ether, fluorine-containing ether; The mass percentage of the additive A in the electrolyte is 0.01%~2%, the mass percentage of the additive B in the electrolyte is 0.01%~2%, and the mass percentage of the additive C in the electrolyte is 7%~20%; The total content of boron element in the additive B is greater than 200ppm in the mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that, The mass percentage of the additive A in the electrolyte is 0.5%~1.5%.

3. The electrolyte of claim 1, wherein The mass percentage of the additive B in the electrolyte is 0.3%~0.7%.

4. The electrolyte of claim 1, wherein The mass percentage of the additive C in the electrolyte is 10%~15%.

5. The electrolyte of claim 2, wherein, The additive A is allyl isocyanurate, and the mass percentage of the additive A in the electrolyte is 1%.

6. The electrolyte of claim 3, wherein The additive B is any one of difluoroborane oxy difluoroborane and fluorine dimethoxy boron hydride, and the mass percentage of the additive B in the electrolyte is 0.5%.

7. The electrolyte of claim 1, wherein The electrolyte salt is lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluoro oxalate borate, lithium difluoro di-oxalate phosphate, lithium bis-trifluoromethyl sulfonyl imide, lithium bis-fluorosulfonyl imide and lithium difluorophosphate; the organic solvent is a mixture of ethylene carbonate, propylene carbonate, diethyl carbonate and propyl propionate; and the concentration of the lithium salt in the electrolyte is 0.9mol / L~2mol / L.

8. The electrolyte according to claim 7, characterized in that The concentration of the lithium salt in the electrolyte is 1.0mol / L~1.3mol / L.

9. A lithium-ion battery, characterized by The electrolyte includes the electrolyte according to any one of claims 1~8.

Images