An electrolyte additive, an electrolyte, and a battery

Abstract

The present invention discloses an electrolyte additive, an electrolyte and a battery. The electrolyte additive of the present invention can improve the rate performance and cycling performance of the battery.

Description

Technical Field

[0001] The present invention relates to the field of lithium battery preparation, and particularly to an electrolyte additive, an electrolyte and a battery. Background Art

[0002] With the progress of the national economy and technology, more and more electronic products or devices need to use lithium-ion batteries.

[0003] The market demand for lithium-ion batteries with high energy density has become more urgent. In order to achieve the high energy density of lithium-ion batteries, in the prior art, it is generally achieved by increasing the working voltage of lithium-ion batteries or developing cathode materials with higher specific capacity.

[0004] In the commercial cobalt lithium oxide high-voltage system (4.5V), there is no mature electrolyte available for matching. Currently, the commonly used lithium-ion battery electrolytes will react with the cathode material in the high-voltage battery system and then be oxidized and decomposed, generating gas and causing volume expansion, ultimately affecting the cycle performance of lithium-ion batteries. Therefore, the commonly used electrolytes cannot be applied to high-voltage lithium-ion battery systems, which severely limits the application of lithium-ion batteries. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides an electrolyte additive for adding to an electrolyte, which can improve the solvation ability of the electrolyte and thus enhance the rate performance and cycle performance.

[0006] Furthermore, it is necessary to provide an electrolyte added with the above electrolyte additive;

[0007] Furthermore, it is necessary to provide a battery using the above electrolyte.

[0008] The technical solution of the present invention is as follows:

[0009] An electrolyte additive,

[0010] comprising additive A and additive B:

[0011] wherein, the additive A is selected from the compound of formula I or / and the compound of formula II:

[0012]

[0013] wherein, R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 , R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17and R 18 are each independently selected from one of H, a halogen atom, an alkyl group having 1 to 10 carbon atoms, an unsaturated hydrocarbon group having 2 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, and an alkanoyl group having 2 to 10 carbon atoms, and H in the alkyl group, the unsaturated hydrocarbon group, the alkoxy group, and the alkanoyl group may be partially or completely substituted by one or more of a halogen atom, a cyano group, a carboxyl group, and a sulfonic acid group;

[0014] The additive B is one or more of ethylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, ethylene sulfate, propylene sulfite, and 4-methyl ethylene sulfite, succinonitrile, adiponitrile, and 1,3,6-hexanetricarbonitrile.

[0015] Wherein, the mass ratio of the additive A to the additive B is (1-5):(1-5), the mass ratio of the additive A to the additive B is preferably 1:3, and the mass ratio of the additive A to the additive B is more preferably 1:2.

[0016] Wherein, the additive A includes a compound of formula I and a compound of formula II, and the mass ratio of the compound of formula I to the compound of formula II is 2:1.

[0017] An electrolyte solution, comprising a lithium salt, an organic solvent, and the above-mentioned electrolyte additive.

[0018] Wherein, for the electrolyte solution as described above, the weight ratio of the lithium salt, the organic solvent, and the electrolyte additive is 14:83:3.

[0019] Wherein, the mass of the electrolyte additive accounts for 2% to 10% of the total mass of the electrolyte solution.

[0020] Wherein, the organic solvent includes a cyclic organic solvent and a chain-like organic solvent, the cyclic organic solvent is one or more of ethylene carbonate, propylene carbonate, and butylene carbonate, and the chain-like organic solvent is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and propyl propionate.

[0021] Wherein, the lithium salt is one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, and lithium difluoro(oxalato)borate. A battery, comprising the above-mentioned electrolyte solution, a positive electrode, a negative electrode, and a separator.

[0022] Compared with the prior art, the electrolyte additive of the present invention comprises additive A and additive B. Among them, additive A is selected from one or more of the first compound represented by formula I and the second compound represented by formula II, and is combined with additive B as the electrolyte additive. Its main function is that additive A (sulfonyl group and / or Si-N bond in formula II) forms a stable interfacial film on the surfaces of the positive and negative electrodes. The organic lithium-rich interfacial film formed on the positive electrode can effectively inhibit the dissolution of transition metals in the positive electrode, reduce the loss of active substances and the increase of resistance, thereby improving the high-temperature storage and cycling performance of the battery. In addition, additive A (Si-N bond in formula II) can spontaneously react with trace water and hydrofluoric acid in the electrolyte to inhibit the hydrolysis of lithium hexafluorophosphate and prevent the corrosion of the positive electrode material by products such as hydrofluoric acid and phosphorus pentafluoride, improving the stability of the material and the electrolyte. Furthermore, the introduction of the ether functional group in formula I of additive A improves the oxidation stability of the electrolyte, and the electron-withdrawing functional group -CH2CF3 improves the oxidation stability of the ether. The -O- atoms in the five-membered ring and the -O- atoms in the linear ether chain segment provide binding sites for Li + and improve the solvation ability of the electrolyte, thereby enhancing the rate and cycling performance. The synergistic use of additive A and additive B forms a more uniform and dense SEI film with a small impedance, thus further improving the rate, high-temperature storage and cycling performance of the battery.

[0023] The electrolyte additive of the present invention can significantly improve the rate, high-temperature storage and cycling performance of the battery. The prepared battery is used in a high-voltage system (4.5V), and its cycling capacity retention rate and rate performance are both significantly improved. Detailed Embodiments

[0024] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0025] Sources of substances:

[0026] Formula I: CAS No. 149099-23-0, Shanghai Yeehoo Biotechnology Co., Ltd.;

[0027] Formula II: CAS No. 82113-66-4, Hubei Yunmei Technology Co., Ltd.;

[0028] The remaining substances are all commercially available.

[0029] Example 1

[0030] Positive electrode preparation: The positive electrode material 4.5V high voltage LiCoO2, binder PVDF (polyvinylidene fluoride), and conductive agent Super-P are dispersed in NMP (N-methylpyrrolidone) organic solvent at a mass ratio of 98:1:1, stirred until stable and uniform under the action of a vacuum mixer, and evenly coated on an aluminum foil with a thickness of 10μm. After the aluminum foil is dried at room temperature, it is transferred to a 120℃ forced air oven and dried for 1h, and then cold pressed and die-cut to form a positive electrode sheet;

[0031] Negative electrode preparation: Commercial graphite, binder PVDF, and conductive agent Super-P were mixed together in a mass ratio of 97:2:1, dispersed in NMP organic solvent, and evenly coated on a copper foil with a thickness of 8μm. The aluminum foil was dried at room temperature and transferred to a 120℃ forced air oven for drying for 1h, and then cold pressed and die-cut to form a negative electrode sheet;

[0032] Electrolyte preparation:

[0033] 1) In a glove box filled with nitrogen (O2 < 2ppm, H2O < 3ppm), an organic solvent is prepared, wherein the organic solvent is composed of EC (ethylene carbonate), PC (propylene carbonate), DMC (dimethyl carbonate), and PP (propyl propionate) in a weight ratio of 10:20:20:50;

[0034] 2) Slowly add LiPF6 to the organic solvent to prepare a lithium salt solution with a concentration of 1.12 mol / L;

[0035] 3) lithium salt (LiPF6), organic solvent, additive A and additive B (FEC fluoroethylene carbonate) were mixed in weight proportions of 14 parts, 83 parts, 1 part and 2 parts to prepare an electrolyte;

[0036] Wherein, additive A is a mixture of a compound of formula I (Formula I) and a compound of formula II (Formula II), wherein the weight ratio of the compound of formula I to the compound of formula II is 2:1, and its structure is shown below:

[0037]

[0038] (In Formula I, R1 is ethyl, R2, R3, R4, R5, R6, R7, R8, R9 are H, R 10 , R 11 , R 12 , R 16 , R 17 and R 18 For F, R 13 , R 14 , R 15 Methyl)

[0039] Preparation of lithium-ion batteries: stack the positive electrode, separator, and negative electrode in order, wind them to get a bare battery cell, and then package them with aluminum-plastic film, bake them again, inject liquid, let them stand, form them, shape them with a fixture, seal them again, and test their capacity to complete the preparation of a high-voltage lithium cobalt oxide 4.5V lithium-ion battery.

[0040] Example 2

[0041] The difference from Example 1 is that the weight proportions of the lithium salt solution, the organic solvent, the additive A and the additive B (FEC fluoroethylene carbonate) are 14 parts, 81 parts, 3 parts and 2 parts respectively.

[0042] The rest is the same as in Example 1 and will not be described again here.

[0043] Example 3

[0044] The difference from Example 1 is that the weight proportions of the lithium salt solution, the organic solvent, the additive A and the additive B (FEC fluoroethylene carbonate) are 14 parts, 79 parts, 5 parts and 2 parts respectively.

[0045] The rest is the same as in Example 1 and will not be described again here.

[0046] Example 4

[0047] The difference from Example 1 is that the weight proportions of the lithium salt solution, the organic solvent, the additive A and the additive B (FEC fluoroethylene carbonate) are 14 parts, 77 parts, 7 parts and 2 parts respectively.

[0048] The rest is the same as in Example 1 and will not be described again here.

[0049] Example 5

[0050] The difference from Example 1 is that additive A is a mixture of a compound of formula I (Formula I) and a compound of formula II (Formula III), wherein the weight ratio of the compound of formula I to the compound of formula II is 2:1,

[0051]

[0052] (R1 is ethyl, R2, R3, R4, R5, R6, R7, R8, R9 are H, R 10 , R 11 , R 12 , R 16 , R 17 and R 18 For F, R 13 , R 14 , R 15 Methyl)

[0053] The rest is the same as in Example 1 and will not be described again here.

[0054] Example 6

[0055] It is different from Example 1 in that: Additive A only includes the compound of Formula I, and the structure is as follows:

[0056]

[0057] Formula I (R1 is ethyl, R2, R3, R4, R5, R6, R7, R8, R9 are H)

[0058] The rest is the same as Example 1 and will not be elaborated here.

[0059] Example 7

[0060] It is different from Example 1 in that: Additive A only includes the compound of Formula II, and the structural formula is as follows:

[0061]

[0062] Formula II (R 10 , R 11 , R 12 , R 16 , R 17 and R 18 are F, R 13 , R 14 , R 15 are methyl)

[0063] The rest is the same as Example 1 and will not be elaborated here.

[0064] Example 8

[0065] It is different from Example 1 in that: The weight ratio of the compound of Formula I to the compound of Formula II is 1:1.

[0066] The rest is the same as Example 1 and will not be elaborated here.

[0067] Example 9

[0068] It is different from Example 1 in that: The weight ratio of the compound of Formula I to the compound of Formula II is 1:2.

[0069] The rest is the same as Example 1 and will not be elaborated here.

[0070] Example 10

[0071] It is different from Example 1 in that: The weight ratio of the compound of Formula I to the compound of Formula II is 1:3.

[0072] The rest is the same as Example 1 and will not be elaborated here.

[0073] Example 11

[0074] The difference from Example 1 is that the weight ratio of the compound of Formula I to the compound of Formula II is 1:5.

[0075] The rest is the same as in Example 1 and will not be elaborated here.

[0076] Example 12

[0077] The difference from Example 1 is that the weight ratio of the compound of Formula I to the compound of Formula II is 3:1.

[0078] The rest is the same as in Example 1 and will not be elaborated here.

[0079] Example 13

[0080] The difference from Example 1 is that the weight ratio of the compound of Formula I to the compound of Formula II is 5:1.

[0081] The rest is the same as in Example 1 and will not be elaborated here.

[0082] Comparative Example 1

[0083] The difference from Example 1 is that additive A is not added to the electrolyte, and the raw materials for preparing the electrolyte are a lithium salt solution, an organic solvent, and additive B in weight portions of 14 parts, 84 parts, and 2 parts.

[0084] The rest is the same as in Example 1 and will not be elaborated here.

[0085] Comparative Example 2

[0086] The difference from Example 1 is that additive B (FEC fluoroethylene carbonate) is not added to the electrolyte, and the raw materials for preparing the electrolyte are a lithium salt (LiPF6), an organic solvent, and additive A in weight portions of 14 parts, 84 parts, and 2 parts.

[0087] The rest is the same as in Example 1 and will not be elaborated here.

[0088] Comparative Example 3

[0089] The difference from Example 1 is that the organic solvent consists of EC (ethylene carbonate) and EMC (ethyl methyl carbonate) with a weight ratio of 30:70, the total weight fraction of the solvent is 79 parts; the weight portion of the lithium salt (LiPF6) is 20 parts; the weight portion of additive A is 1 part, and additive A only includes the compound of Formula IV, and the structure is as follows:

[0090]

[0091] The rest is the same as in Example 1 and will not be elaborated here.

[0092] Comparative Example 4

[0093] The difference from Example 1 is that the organic solvent consists of EC (ethylene carbonate), DEC (diethyl carbonate), and DMC (dimethyl carbonate) with a weight ratio of 30:20:50, and the total mass fraction of the solvent is 83 parts; the weight fraction of LiPF6 lithium salt is 12 parts, and the weight fractions of lithium salt additives LiFSI and LiDFP are 3 parts; additives A and B (FEC fluoroethylene carbonate) are 0.5 parts and 1 part by weight, and additive A only includes the compound of formula V.

[0094]

[0095] The rest is the same as Example 1 and will not be elaborated here.

[0096] Testing method

[0097] The batteries prepared in Examples 1 - 13 and Comparative Examples 1 - 4 were subjected to the following tests, and the results are listed in the following table.

[0098] 1. Room temperature / high temperature cycle test:

[0099] The batteries were placed in an oven at a constant temperature of -10°C / 25°C / 45°C for 4 hours respectively, then charged at a constant current of 0.5C to 4.5V, then charged at a constant voltage until the current dropped to 0.05C, and then discharged at a constant current of 1C to 3.0V. Such cycles were carried out, and the initial capacity of the battery and the discharge capacity of the last cycle (the 20th cycle or the 500th cycle) were recorded.

[0100] Cycle capacity retention rate = discharge capacity of the last cycle / initial capacity × 100%.

[0101] 2. Performance test after storage at 60°C:

[0102] The batteries were charged at a constant current of 0.5C to 4.5V in a 25°C environment, charged at a constant voltage until the current dropped to 0.02C, and then discharged at a constant current of 0.2C to 3.0V. The cell thickness, internal resistance, and initial capacity were recorded; charged to 4.5V in the same way, then placed in an oven at a constant temperature of 60°C for 7 days. After 7 days, the cell thickness, internal resistance were measured, and the capacity discharged at a current of 0.2C to 3.0V was recorded as the residual capacity. The stored cells were charged at a constant current of 0.5C to 4.5V, charged at a constant voltage until the current dropped to 0.02C, and then discharged at a constant current of 0.2C to 3.0V, which was recorded as the recovery capacity.

[0103] Capacity residual rate = residual capacity / initial capacity × 100%,

[0104] Capacity recovery rate = recovery capacity / initial capacity × 100%,

[0105] Thickness swelling rate = (thickness after storage - thickness before storage) / thickness before storage × 100%,

[0106] Internal resistance growth rate = (internal resistance after storage - internal resistance before storage) / internal resistance before storage × 100%.

[0107] 3. Rate performance:

[0108] Charge the battery at a constant current of 0.5C to 4.5V in an environment of 25°C, then charge at a constant voltage until the current drops to 0.02C, and then discharge at a constant current of 0.2C / 1C / 2C / 3C / 5C to 3.0V respectively. Record the discharge capacity of the battery cell.

[0109] Capacity retention rate at different rates = discharge capacity at different rates / initial capacity at 0.2C × 100%.

[0110] Cycle capacity retention rate and rate performance

[0111]

[0112]

[0113] Performance test after storage at 60°C

[0114]

[0115] * Note: In the table, / indicates that there is no test result for this performance in this comparative example.

[0116] It can be seen from the data in the above table that by applying the additive of the present invention in the preparation of lithium-ion batteries, the cycle performance and rate performance of lithium-ion batteries can be effectively improved.

[0117] The main reason is that additive A (sulfonyl group and Si-N bond in formula II) forms a stable interfacial film on the surfaces of the positive and negative electrodes. The organic lithium-rich interfacial film formed on the positive electrode can effectively inhibit the dissolution of transition metals in the positive electrode, reduce the loss of active substances and the increase of resistance, thereby improving the high-temperature storage and cycle performance of the battery. In addition, additive A (Si-N bond in formula II) can spontaneously react with trace water and hydrofluoric acid in the electrolyte, inhibit the hydrolysis of lithium hexafluorophosphate, prevent the corrosion of the positive electrode material by products such as hydrofluoric acid and phosphorus pentafluoride, and improve the stability of the material and the electrolyte. In addition, the introduction of the ether functional group of additive A improves the oxidation stability of the electrolyte, and the electron-withdrawing functional group -CH2CF3 improves the oxidation stability of the ether. The -O- atoms in the five-membered ring and the -O- atoms in the linear ether chain segment are for Li +Binding sites are provided, which improve the solvation ability of the electrolyte, thereby enhancing the rate and cycling performance. The synergistic use of additive A and additive B forms a more uniform and dense SEI film with low impedance, thus further improving the rate, high-temperature storage and cycling performance of the battery. The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An electrolyte additive, characterized in that: It includes additive A and additive B: Wherein, the additive A is selected from the compounds of formula I and formula II: Formula I, Formula II; Among them, R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 , R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 and R 18 are each independently selected from one of H, a halogen atom, an alkyl group having 1 to 10 carbon atoms, an unsaturated hydrocarbon group having 2 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, and an alkanoyl group having 2 to 10 carbon atoms, and H in the alkyl group, the unsaturated hydrocarbon group, the alkoxy group, and the alkanoyl group may be partially or completely substituted by one or more of a halogen atom, a cyano group, a carboxyl group, and a sulfonic acid group; The additive B is one or more of ethylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, ethylene sulfate, propylene sulfite, 4-methyl ethylene sulfate, succinonitrile, adiponitrile, 1,3,6-hexanetricarbonitrile; The mass ratio of the compound of formula I to the compound of formula II is 2:

1.

2. The electrolyte additive according to claim 1, characterized in that: The mass ratio of the additive A to the additive B is (1-5):(1-5).

3. An electrolyte, comprising a lithium salt, an organic solvent and the electrolyte additive according to any one of claims 1-2.

4. The electrolyte according to claim 3, wherein: The weight ratio of the lithium salt, the organic solvent and the electrolyte additive is 14:83:

3.

5. The electrolyte according to claim 3, characterized in that: The mass of the electrolyte additive accounts for 2% to 10% of the total mass of the electrolyte.

6. The electrolyte according to claim 5, characterized in that: The organic solvent includes a cyclic organic solvent and a chain organic solvent. The cyclic organic solvent is one or more of ethylene carbonate, propylene carbonate and butylene carbonate, and the chain organic solvent is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and propyl propionate.

7. The electrolyte according to claim 6, characterized in that: The lithium salt is one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate and lithium difluoro(oxalato)borate.

8. A battery, characterized in that It includes the electrolyte according to any one of claims 3-7, a positive electrode, a negative electrode and a separator.

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