High-voltage lithium cobalt oxide lithium ion battery electrolyte and lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and discloses a high-voltage lithium cobalt oxide lithium ion battery non-aqueous electrolyte and a lithium ion battery. The high-voltage lithium cobalt oxide lithium ion battery non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte lithium salt and an additive, wherein the additive comprises a conventional additive and a cyanogen additive with a structure as shown in a formula I or a formula II. The cyanide additive in the electrolyte can form a positive electrode film and inhibit dissolution of metal ions in a positive electrode material, and meanwhile, an N element in cyano in the additive contains lone electron pairs which can chelate cobalt ions dissolved out of the positive electrode material, so that the metal ions are prevented from being migrated to a negative electrode graphite interface to catalyze reductive decomposition of the electrolyte; meanwhile, other functional groups contained in the additive can also participate in negative electrode film formation, so that the dynamic characteristics and thermodynamic characteristics of a passive film are improved, and the electrochemical performance of the lithium ion battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a high-voltage lithium cobalt oxide lithium ion battery electrolyte and a lithium ion battery. Background Art

[0002] Lithium-ion batteries are widely used in 3C digital products due to their advantages such as high operating voltage, high energy density, long life, wide operating temperature range and environmental friendliness. Nowadays, thinness and high energy density are gradually becoming the development trend of batteries, especially for 3C digital products. In order to improve the energy density of lithium-ion batteries, a common measure is to increase the charging cut-off voltage of the positive electrode material, such as the voltage of commercial lithium cobalt oxide lithium-ion batteries from 4.2V→4.35V→4.4V→4.45V→4.48V→4.5V.

[0003] However, positive electrode materials have certain defects under high voltage. For example, high voltage positive electrode active materials have strong oxidizing properties when they are in the lithium-deficient state, and the electrolyte is easily oxidized and decomposed, generating a large amount of gas and heat. In addition, high voltage positive electrode active materials are also very unstable when they are in the lithium-deficient state, and are prone to some side reactions, such as oxygen release and transition metal ion dissolution. Therefore, it is necessary to develop new film-forming additives, especially additives that can form positive electrode films and protect positive electrode materials. Summary of the invention

[0004] In view of the deficiencies and needs of the prior art, the present invention provides a high-voltage lithium cobalt oxide lithium ion battery electrolyte and a lithium ion battery. The cyanide additive in the electrolyte of the present invention can form a positive electrode film and inhibit the dissolution of metal ions (cobalt ions) in the positive electrode material. At the same time, the N element in the cyanide group in the additive contains a lone electron pair, which can chelate with the cobalt ions dissolved in the positive electrode material to prevent the metal ions from migrating to the negative electrode graphite interface to catalyze the reduction and decomposition of the electrolyte, thereby improving the electrochemical performance of the lithium ion battery. In addition, other functional groups contained in the additive of the present invention can also participate in the negative electrode film formation, improve the kinetic characteristics and thermodynamic characteristics of the passivation film (SEI), and thus enhance the electrochemical performance of the lithium ion battery.

[0005] In order to achieve the above object, the non-aqueous electrolyte of the high-voltage lithium cobalt oxide lithium ion battery of the present invention comprises a non-aqueous organic solvent, an electrolyte lithium salt and an additive, wherein the additive comprises a conventional additive and a cyanide additive having a structure of Formula I or Formula II:

[0006]

[0007] Wherein, R1, R2, and R3 are independently selected from alkyl, alkenyl, alkynyl, aromatic hydrocarbons and halogenated derivatives thereof.

[0008] Furthermore, the cyanide additive having the structure of Formula I or Formula II is selected from one or more of Compound (1) to Compound (4):

[0009]

[0010] Preferably, the content of the cyanide additive having the structure of Formula I or Formula II accounts for 0.5 to 3.0% of the total mass of the electrolyte, for example, 1.0 to 2.0%.

[0011] Further, in some embodiments of the present invention, the conventional additives are selected from one or more of fluoroethylene carbonate (FEC), succinonitrile (SN), adiponitrile (ADN), 1,3,6-hexanetrinitrile (HTCN), 1,2-bis(cyanoethoxy)ethane (DENE), 1,3-propane sultone (PS), 1,3-propylene sultone (PST), vinyl vinylene carbonate (VEC), divinyl sulfate (DTD), tris(trimethylsilyl)borate (TMSB), tris(trimethylsilyl)phosphate (TMSP), and methylene disulfonate (MMDS).

[0012] Furthermore, in some embodiments of the present invention, the amount of the conventional additive added is 5.0% to 20.0% of the total mass of the electrolyte.

[0013] Preferably, in some embodiments of the present invention, when the conventional additives are included, the added amount of the fluoroethylene carbonate accounts for 3.0% to 10.0% of the total mass of the electrolyte; the added amount of the 1,3-propane sultone accounts for 1.0 to 5.0% of the total mass of the electrolyte; the added amount of the nitrile additives such as succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, etc. accounts for 0.5% to 4.0% of the total mass of the electrolyte, and the added amount of other additives containing unsaturated bonds accounts for 0.1 to 1.0% of the total mass of the electrolyte.

[0014] More preferably, in some embodiments of the present invention, the conventional additives are 5.0-9.0% of fluoroethylene carbonate, 1.5-4.5% of 1,3-propane sultone, 1.0-3.0% of adiponitrile and 0.5-1.5% of 1,2-bis(cyanoethoxy)ethane; or 5.0-9.0% of fluoroethylene carbonate, 2.0-6.0% of 1,3-propane sultone, 1.0-3.0% of adiponitrile, 0.5-2.5% of 1,2-bis(cyanoethoxy)ethane and 0.5-1.5% of vinyl sulfate.

[0015] Further preferably, in some embodiments of the present invention, the conventional additives are 6.0-8.0% of fluoroethylene carbonate, 2.5-3.5% of 1,3-propane sultone, 1.5-2.5% of adiponitrile and 0.8-1.2% of 1,2-bis(cyanoethoxy)ethane, accounting for 6.0-8.0% of the total mass of the electrolyte, 3.0-5.0% of 1,3-propane sultone, 1.5-2.5% of adiponitrile, 1.0-2.0% of 1,2-bis(cyanoethoxy)ethane and 0.8-1.2% of vinyl sulfate.

[0016] Furthermore, in some embodiments of the present invention, the electrolyte lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorophosphate.

[0017] Furthermore, in some embodiments of the present invention, the added amount of the electrolyte lithium salt accounts for 12.5-18.0% of the total mass of the electrolyte.

[0018] Preferably, in some embodiments of the present invention, the electrolyte lithium salt is a mixed lithium salt of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide and lithium difluorophosphate, the addition amount of the lithium hexafluorophosphate accounts for 12.0% to 16.0% of the total mass of the electrolyte, the addition amount of the lithium bisfluorosulfonyl imide accounts for 1.0% to 3.0% of the total mass of the electrolyte, and the addition amount of the lithium difluorophosphate accounts for 0.2% to 0.8% of the total mass of the electrolyte; more preferably, the addition amount of the lithium hexafluorophosphate accounts for 13.0% to 15.0% of the total mass of the electrolyte, the addition amount of the lithium bisfluorosulfonyl imide accounts for 1.5% to 2.5% of the total mass of the electrolyte, and the addition amount of the lithium difluorophosphate accounts for 0.35% to 0.65% of the total mass of the electrolyte.

[0019] Furthermore, in some embodiments of the present invention, the non-aqueous organic solvent is selected from one or more of carbonate solvents, carboxylate solvents, fluorocarbonate solvents, fluorocarboxylate solvents and fluoroether solvents.

[0020] Further, in some embodiments of the present invention, the carbonate solvent includes cyclic carbonate and chain carbonate; wherein the cyclic carbonate solvent includes one or more of ethylene carbonate and propylene carbonate; the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; the carboxylate solvent includes one or more of ethyl acetate, n-propyl acetate, ethyl propionate and propyl propionate.

[0021] Furthermore, in some embodiments of the present invention, the non-aqueous organic solvent contains ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate and propyl propionate; preferably, the mass ratio of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate and propyl propionate in the non-aqueous organic solvent is 5-15:10-20:10-30:15-25:30-40.

[0022] On the other hand, the present invention also provides a high-voltage lithium cobalt oxide lithium ion battery, the high-voltage lithium cobalt oxide lithium ion battery comprising a battery core formed by laminating or winding a positive electrode sheet, a separator and a negative electrode sheet, and the above-mentioned high-voltage lithium cobalt oxide lithium ion battery electrolyte of the present invention, wherein the positive electrode active material of the positive electrode sheet is a lithium cobalt oxide active material, and the compaction density of the positive electrode sheet is 4.0 to 4.45 g / cm 3 .

[0023] Furthermore, the negative electrode active material of the negative electrode sheet is artificial graphite, natural graphite or composite graphite, and the compaction density of the negative electrode sheet is 1.5 to 1.75 g / cm 3 .

[0024] Compared with the prior art, the advantages of the present invention mainly lie in that the N atom on the cyanide group of the cyanide additive of the present invention has a lone electron pair, which can chelate with the cobalt ions overflowing from the positive electrode material to prevent the cobalt ions from migrating to the negative electrode and catalyze the reduction and decomposition reaction of the electrolyte. The cyanide additive of the present invention also contains derivative ester substances such as sulfur or phosphorus, which can better participate in the formation of the negative electrode interface passivation film, thereby improving the kinetic characteristics and thermodynamic characteristics of the passivation film and enhancing the electrochemical performance of the lithium ion battery. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiments. Additional aspects and advantages of the present invention will be given in part in the following description, and part will become apparent from the following description, or will be understood through the practice of the present invention. It should be understood that the following description is only used to explain the present invention and is not intended to limit the present invention.

[0026] As used herein, the terms "comprises," "including," "contains," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0027] When amount, concentration or other value or parameter is expressed as range, preferred range or a series of upper preferred value and lower preferred value limit range, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when disclosing range "1 to 5", described range should be interpreted as including range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the range is intended to include its end value and all integers and fractions within the range.

[0028] Singular forms include plural references unless the context clearly indicates otherwise. "Optional" or "either" means that the subsequently described event or incident may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

[0029] The indefinite articles "a" and "an" before the elements or components of the present invention have no limitation on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the quantity obviously refers to the singular form only.

[0030] Example 1

[0031] Preparation of the electrolyte: In a glove box filled with argon, ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate and propyl propionate were mixed in a mass ratio of EC:PC:DEC:EP:PP=10:15:20:20:35, and then 14.0wt% of lithium hexafluorophosphate, 2.0% of lithium bis(fluorosulfonyl)imide and 0.5% of lithium difluorophosphate were slowly added to the mixed solution, and finally 1.5wt% of the cyanide additive (Compound 1) was added to the total mass of the electrolyte. After stirring evenly, the lithium ion battery electrolyte of Example 1 was obtained.

[0032] Preparation of lithium-ion batteries:

[0033] The positive electrode active material lithium cobalt oxide, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96:2:2, and then coated on an aluminum foil, dried, and cold pressed to obtain a positive electrode sheet.

[0034] The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are fully stirred and mixed in a deionized water solvent system in a mass ratio of 96:2.5:0.5:1, and then coated on a copper foil, dried, and cold pressed to obtain a negative electrode sheet.

[0035] Polyethylene (PE) is used as a base film and a nano-aluminum oxide coating is coated on the base film as an isolation film.

[0036] The positive electrode sheet, the isolation film and the negative electrode sheet are stacked in sequence and then wound in the same direction to obtain a bare cell, the bare cell is placed in an outer package, the prepared electrolyte is injected, and a high-voltage lithium cobalt oxide lithium-ion battery is obtained after packaging, 45°C storage, high-temperature fixture formation, secondary packaging, and capacity division.

[0037] Examples 2-8 and Comparative Examples 1-5

[0038] In Examples 2-8 and Comparative Examples 1-5, except that the components of the electrolyte are added in the proportions shown in Table 1, the rest are the same as in Example 1.

[0039] Table 1 Composition ratio of each component of the electrolyte of Examples 1-8 and Comparative Examples 1-5

[0040]

[0041] Effect test

[0042] 1) Normal temperature cycle performance test: At 25°C, charge the divided battery to 4.45V at 0.5C constant current and constant voltage, with a cut-off current of 0.05C, and then discharge it to 3.0V at 0.7C constant current. Repeat this cycle. After 500 charge / discharge cycles, calculate the 500th cycle capacity retention rate. The calculation formula is as follows:

[0043] 500th cycle capacity retention rate (%) = (500th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0044] 2) 85℃ constant temperature storage capacity remaining rate test: First, the battery is charged and discharged once at 0.5C at room temperature (4.45V~3.0V), and the discharge capacity C0 of the battery before storage is recorded. Then the battery is charged to 4.45V full power state with constant current and constant voltage, and then the battery is placed in an 85℃ constant temperature box for 4h. After the storage is completed, the battery is taken out; after the battery is cooled at room temperature for 24h, the battery is discharged to 3.0V at 0.5C constant current again, and the discharge capacity C1 of the battery after storage is recorded. The capacity remaining rate of the battery after 85℃ constant temperature storage for 4h is calculated. The calculation formula is as follows:

[0045] After 4h storage at 85℃, the remaining capacity = C1 / C0*100%.

[0046] 3) 45℃ cycle performance test: At 45℃, charge the divided battery to 4.45V at 0.5C constant current and constant voltage, with a cut-off current of 0.05C, and then discharge it to 3.0V at 0.7C constant current. Repeat this cycle. After 300 cycles of charge / discharge, calculate the 300th cycle capacity retention rate. The calculation formula is as follows:

[0047] 300th cycle capacity retention rate (%) = (300th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0048] Table 2 Battery performance test results of each embodiment

[0049]

[0050]

[0051] From the electrochemical performance of Examples 1-4 and Comparative Example 1 in Table 2, it can be seen that the cyanide additives of the present invention can improve the electrochemical performance of the LCO-4.45V battery, but the effect of using the cyanide additives of the present invention alone is not particularly good.

[0052] From the electrochemical performance of Example 1, Examples 5-6 and Comparative Examples 2-3 in Table 2, it can be seen that the addition amount of the cyanide additive of the present invention is more appropriately 0.5% to 3.0%. If the addition amount exceeds the amount of the present invention, the expected experimental effect cannot be achieved.

[0053] From the electrochemical performance of Example 1 and Example 7-8 in Table 2, it can be seen that the cyanide additives of the present invention are used in combination with other types of additives to have better effects, mainly because the cyanide additives of the present invention can form positive electrode films and inhibit the dissolution of metal ions (cobalt ions) in positive electrode materials. At the same time, the N element in the cyanide group of the additive contains lone electron pairs, which can chelate with the cobalt ions dissolved in the positive electrode material to prevent the migration of metal ions to the negative electrode graphite interface to catalyze the reduction and decomposition of the electrolyte, thereby improving the electrochemical performance of lithium ion batteries. The substance having the structure of formula (I) also contains sulfur and phosphorus derivative ester substances, which can better participate in the formation of the negative electrode interface passivation film, thereby improving the kinetic characteristics and thermodynamic characteristics of the passivation film (SEI) and improving the electrochemical performance of lithium ion batteries.

[0054] It is easy for a person skilled in the art to understand that, according to the disclosure and teaching of the above description, a person skilled in the art to which the present invention belongs can also change and modify the above implementation mode, and any modification, equivalent replacement and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of explanation and do not constitute any limitation to the present invention.

Claims

1. A high voltage lithium cobalt oxide lithium ion battery non-aqueous electrolyte, characterized in that: The non-aqueous electrolyte of the high-voltage lithium cobalt oxide lithium ion battery comprises a non-aqueous organic solvent, an electrolyte lithium salt and an additive, wherein the additive comprises a conventional additive and a cyanide additive having a structure of Formula I or Formula II: Wherein, R1, R2, and R3 are independently selected from alkyl, alkenyl, alkynyl, aromatic hydrocarbons and halogenated derivatives thereof.

2. The high voltage lithium cobalt oxide lithium ion battery non-aqueous electrolyte according to claim 1, characterized in that: The cyanide additive having the structure of Formula I or Formula II is selected from one or more of Compound (1) to Compound (4): Preferably, the content of the cyanide additive having the structure of Formula I or Formula II accounts for 0.5 to 3.0% of the total mass of the electrolyte, for example, 1.0 to 2.0%.

3. The high voltage lithium cobalt oxide lithium ion battery non-aqueous electrolyte according to claim 1, characterized in that: The conventional additives are selected from one or more of fluoroethylene carbonate (FEC), succinonitrile (SN), adiponitrile (ADN), 1,3,6-hexanetrinitrile (HTCN), 1,2-bis(cyanoethoxy)ethane (DENE), 1,3-propane sultone (PS), 1,3-propylene sultone (PST), vinyl vinylene carbonate (VEC), divinyl sulfate (DTD), tris(trimethylsilyl)borate (TMSB), tris(trimethylsilyl)phosphate (TMSP), and methylene disulfonate (MMDS); preferably, the addition amount of the conventional additives accounts for 5.0% to 20.0% of the total mass of the electrolyte.

4. The high voltage lithium cobalt oxide lithium ion battery non-aqueous electrolyte according to claim 1, characterized in that: When the conventional additives are included, the added amount of the fluoroethylene carbonate accounts for 3.0% to 10.0% of the total mass of the electrolyte; the added amount of the 1,3-propane sultone accounts for 1.0 to 5.0% of the total mass of the electrolyte; the added amount of the nitrile additives such as succinonitrile, adiponitrile, and 1,3,6-hexanetrinitrile accounts for 0.5% to 4.0% of the total mass of the electrolyte.

5. The high voltage lithium cobalt oxide lithium ion battery non-aqueous electrolyte according to claim 1, characterized in that: The conventional additives are 5.0-9.0% of fluoroethylene carbonate, 1.5-4.5% of 1,3-propane sultone, 1.0-3.0% of adiponitrile and 0.5-1.5% of 1,2-bis(cyanoethoxy)ethane; or 5.0-9.0% of fluoroethylene carbonate, 2.0-6.0% of 1,3-propane sultone, 1.0-3.0% of adiponitrile, 0.5-2.5% of 1,2-bis(cyanoethoxy)ethane and 0.5-1.5% of vinyl sulfate; preferably The conventional additives are 6.0-8.0% of fluoroethylene carbonate, 2.5-3.5% of 1,3-propane sultone, 1.5-2.5% of adiponitrile and 0.8-1.2% of 1,2-bis(cyanoethoxy)ethane; or 6.0-8.0% of fluoroethylene carbonate, 3.0-5.0% of 1,3-propane sultone, 1.5-2.5% of adiponitrile, 1.0-2.0% of 1,2-bis(cyanoethoxy)ethane and 0.8-1.2% of vinyl sulfate.

6. The high voltage lithium cobalt oxide lithium ion battery non-aqueous electrolyte according to claim 1, characterized in that: The electrolyte lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide, and lithium difluorophosphate; preferably, the electrolyte lithium salt is added in an amount of 12.5-18.0% of the total mass of the electrolyte; preferably, the electrolyte lithium salt is a mixed lithium salt of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide and lithium difluorophosphate, the lithium hexafluorophosphate is added in an amount of 12.0-16.0% of the total mass of the electrolyte, the lithium bisfluorosulfonyl imide is added in an amount of 1.0%-3.0% of the total mass of the electrolyte, and the lithium difluorophosphate is added in an amount of 0.2%-0.8% of the total mass of the electrolyte; more preferably, the lithium hexafluorophosphate is added in an amount of 13.0-15.0% of the total mass of the electrolyte, the lithium bisfluorosulfonyl imide is added in an amount of 1.5%-2.5% of the total mass of the electrolyte, and the lithium difluorophosphate is added in an amount of 0.35%-0.65% of the total mass of the electrolyte.

7. The high voltage lithium cobalt oxide lithium ion battery non-aqueous electrolyte according to claim 1, characterized in that: The non-aqueous organic solvent is selected from one or more of carbonate solvents, carboxylate solvents, fluorinated carbonate solvents, fluorinated carboxylate solvents and fluorinated ether solvents; preferably, the carbonate solvent includes cyclic carbonates and chain carbonates; wherein the cyclic carbonate solvent includes one or more of ethylene carbonate and propylene carbonate; the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; the carboxylate solvent includes one or more of ethyl acetate, n-propyl acetate, ethyl propionate and propyl propionate.

8. The high voltage lithium cobalt oxide lithium ion battery non-aqueous electrolyte according to claim 1, characterized in that: The non-aqueous organic solvent comprises ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate and propyl propionate; preferably, the mass ratio of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate and propyl propionate in the non-aqueous organic solvent is 5-15:10-20:10-30:15-25:30-40.

9. A high voltage lithium cobalt oxide lithium ion battery, characterized in that: The high-voltage lithium cobalt oxide lithium-ion battery comprises a battery cell formed by laminating or winding a positive electrode sheet, a separator and a negative electrode sheet, and the high-voltage lithium cobalt oxide lithium-ion battery electrolyte according to any one of claims 1 to 8, wherein the positive electrode active material of the positive electrode sheet is a lithium cobalt oxide active material, and the compaction density of the positive electrode sheet is 4.0 to 4.45 g / cm 3 .

10. The high voltage lithium cobalt oxide lithium ion battery according to claim 9, characterized in that: The negative electrode active material of the negative electrode sheet is artificial graphite, natural graphite or composite graphite, and the compaction density of the negative electrode sheet is 1.5 to 1.75 g / cm 3 .

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