阅读说明：本技术 一种高电压锂离子电池用电解液及包括所述电解液的锂离子电池 (Electrolyte for high-voltage lithium ion battery and lithium ion battery comprising same ) 是由 王龙 王海 母英迪 廖波 曾长安 李素丽 李俊义 徐延铭 于 2019-11-20 设计创作，主要内容包括：本发明提供了一种高电压锂离子电池用电解液及包括所述电解液的锂离子电池,本发明的电解液中加入1,3,6-己烷三腈能够明显提高高电压锂离子电池的循环性能和高温储存性能,通过控制1,3,6-己烷三腈的色度可以控制含有该物质的电解液的色度能够满足锂离子电池电解液生产和储存的色度要求。且当1,3,6-己烷三腈的色度在<150Hazen范围内,所述电解液的色度在国家标准的许可范围内,同时由于电解液中含有-CN基团在正极表面能够与过渡金属更好的结合,从而减少高电压下正极表面与电解液的副反应,提高了高电压锂离子电池的循环和高温储存性能使用该电解液的高电压锂离子电池的具有优异的循环性能。(The invention provides an electrolyte for a high-voltage lithium ion battery and the lithium ion battery comprising the electrolyte, wherein 1,3, 6-hexanetricarbonitrile is added into the electrolyte, so that the cycle performance and the high-temperature storage performance of the high-voltage lithium ion battery can be obviously improved, and the chromaticity of the electrolyte containing the substance can be controlled by controlling the chromaticity of the 1,3, 6-hexanetricarbonitrile, so that the chromaticity requirements of the production and the storage of the electrolyte of the lithium ion battery can be met. And when the chroma of the 1,3, 6-hexanetricarbonitrile is in a range of less than 150Hazen, the chroma of the electrolyte is in an allowable range of national standards, and meanwhile, the electrolyte contains a-CN group which can be better combined with transition metal on the surface of the anode, so that the side reaction of the surface of the anode and the electrolyte under high voltage is reduced, and the cycle performance and the high-temperature storage performance of the high-voltage lithium ion battery using the electrolyte are improved, and the high-voltage lithium ion battery has excellent cycle performance.)

1. An electrolyte, wherein the electrolyte comprises a non-aqueous organic solvent, an additive and a lithium salt, wherein the additive comprises 1,3, 6-hexanetricarbonitrile and fluoroethylene carbonate; the 1,3, 6-hexanetricarbonitrile has a color of <150 Hazen.

2. The electrolyte of claim 1, wherein the 1,3, 6-hexanetricarbonitrile has a color of 100Hazen or less.

3. The electrolyte as claimed in claim 1 or 2, wherein the fluoroethylene carbonate is used in an amount of 5 to 10 wt% based on the total weight of the electrolyte.

4. An electrolyte as claimed in any one of claims 1 to 3, wherein the 1,3, 6-hexanetricarbonitrile is used in an amount of from 0.5 to 6% by weight based on the total weight of the electrolyte.

5. The electrolytic solution according to any one of claims 1 to 4, wherein the non-aqueous organic solvent is a mixture of at least one of cyclic carbonates and at least one of linear carbonates and linear carboxylates, mixed in any proportion.

6. The electrolyte of claim 5, wherein the cyclic carbonate is selected from ethylene carbonate or propylene carbonate, and the linear carbonate and the linear carboxylate are selected from dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl propionate, or propyl acetate.

7. The electrolyte as claimed in any one of claims 1 to 6, wherein the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide and lithium bis (trifluoromethylsulfonyl) imide, and the lithium salt accounts for 13 to 18 wt% of the total mass of the nonaqueous electrolyte.

8. A lithium-ion battery comprising the electrolyte of any of claims 1-7.

9. The lithium ion battery of claim 8, wherein the lithium ion battery further comprises a positive plate, a negative plate, and a separator, wherein the separator is disposed between the positive plate and the negative plate.

10. The lithium ion battery according to claim 9, wherein the positive electrode material has a compacted density of 3.8 to 4.4mg/cm when coated³(ii) a When the negative electrode material is coated, the compacted density of the negative electrode material is 1.5-1.9mg/cm³；

Preferably, the charge cut-off voltage of the lithium ion battery is 4.4V or more.

Technical Field

The invention belongs to the technical field of electrolyte, and particularly relates to electrolyte for a high-voltage lithium ion battery and the lithium ion battery comprising the electrolyte.

Background

Since commercialization, lithium ion batteries have been widely used in the fields of smart phones, tablet computers, smart wearing, electric tools, electric vehicles, and the like. In recent years, consumers have increasingly demanded higher energy density and cycle life of lithium ion batteries, and at the same time, high safety of lithium ion batteries has been demanded.

At present, the energy density of the lithium ion battery is mainly improved by improving the charging voltage of the anode material, but the improvement of the charging voltage has higher and higher requirements on the stability of the anode structure and the electrolyte. The stability of the anode structure is mainly improved by means of doping and cladding; the stability of the electrolyte is improved mainly by optimizing a solvent system and using a high-voltage additive, and the addition of the high-voltage additive is the most common and economic means for the research and development and production of the lithium ion battery electrolyte at present.

The nitrile compound is a common additive for improving the high-temperature cycle performance, and the high-temperature cycle performance of the lithium ion battery can be obviously improved by adding a small amount of nitrile compound into the electrolyte, so that the lithium ion battery which is suitable for high voltage and has better high-temperature cycle performance is prepared. However, taking 1,3, 6-hexanetricarbonitrile as an example, the currently prepared 1,3, 6-hexanetricarbonitrile contains colored impurities and free acid, so that the chromaticity of the 1,3, 6-hexanetricarbonitrile cannot meet the chromaticity requirement of the lithium ion battery electrolyte additive, and the chromaticity of the 1,3, 6-hexanetricarbonitrile-containing electrolyte is increased rapidly along with the prolonging of the storage time, so that the chromaticity of the 1,3, 6-hexanetricarbonitrile-containing electrolyte is overproof. When the chromaticity of the electrolyte is too high, the quality of the electrolyte is deteriorated, which may result in degradation of electrochemical properties, particularly cycle performance and storage performance, of the lithium ion battery.

Disclosure of Invention

The invention aims to solve the problem of poor cycle performance of the existing high-voltage lithium ion battery, and provides an electrolyte for the high-voltage lithium ion battery, which contains a 1,3, 6-hexanetricarbonitrile additive, can improve the cycle performance of the high-voltage lithium ion battery by controlling the chromaticity of the additive to be within a range of less than 150Hazen, and has better high-temperature storage performance.

The purpose of the invention is realized by the following technical scheme:

an electrolyte comprising a non-aqueous organic solvent, an additive and a lithium salt, wherein the additive comprises 1,3, 6-hexanetricarbonitrile and fluoroethylene carbonate; the 1,3, 6-hexanetricarbonitrile has a color of <150 Hazen.

In the invention, the electrolyte is used for a lithium ion battery, in particular for a high-voltage lithium ion battery.

According to the invention, the 1,3, 6-hexanetricarbonitrile has a chroma of < 100Hazen, for example < 90Hazen, for example < 60Hazen, for example < 30 Hazen.

According to the invention, the fluoroethylene carbonate is used in an amount of 5 to 10 wt%, for example 6 to 9 wt%, for example 5 to 8 wt%, based on the total weight of the electrolyte.

According to the invention, the 1,3, 6-hexanetricarbonitrile is used in an amount of from 0.5 to 6% by weight, for example from 0.8 to 5% by weight, for example from 1 to 4% by weight, based on the total weight of the electrolyte.

According to the invention, the non-aqueous organic solvent is a mixture of at least one of cyclic carbonates and at least one of linear carbonates and linear carboxylic acid esters mixed according to any proportion, wherein the cyclic carbonates are ethylene carbonate and propylene carbonate, and the linear carbonates and linear carboxylic acid esters are compounds such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl propionate and propyl acetate.

According to the invention, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide and lithium bis (trifluoromethylsulfonyl) imide. Wherein the lithium salt accounts for 13-18 wt% of the total mass of the nonaqueous electrolyte.

A lithium ion battery comprises the electrolyte.

According to the invention, the lithium ion battery also comprises a positive plate, a negative plate and a diaphragm, wherein the diaphragm is arranged between the positive plate and the negative plate.

In the invention, when the anode material is coated, the compacted density is 3.8-4.4mg/cm³When the negative electrode material is coated, the compacted density of the negative electrode material is 1.5-1.9mg/cm³。

According to the present invention, the charge cut-off voltage of the lithium ion battery is 4.4V or more.

The invention has the beneficial effects that:

the invention provides an electrolyte and a lithium ion battery comprising the same, wherein the electrolyte is particularly suitable for a high-voltage lithium ion battery. The 1,3, 6-hexanetricarbonitrile added into the electrolyte can obviously improve the cycle performance and the high-temperature storage performance of the high-voltage lithium ion battery, and the chromaticity of the electrolyte containing the substance can be controlled by controlling the chromaticity of the 1,3, 6-hexanetricarbonitrile, so that the chromaticity requirements of the production and storage of the lithium ion battery electrolyte can be met. And when the chroma of the 1,3, 6-hexanetricarbonitrile is in a range of less than 150Hazen, the chroma of the electrolyte is in an allowable range of national standards, and meanwhile, the electrolyte contains a-CN group which can be better combined with transition metal on the surface of the anode, so that the side reaction of the surface of the anode and the electrolyte under high voltage is reduced, and the cycle performance and the high-temperature storage performance of the high-voltage lithium ion battery using the electrolyte are improved, and the high-voltage lithium ion battery has excellent cycle performance.

Detailed Description

As described above, the present invention provides an electrolyte solution suitable for a lithium ion battery, particularly for a high voltage lithium ion battery; the electrolyte comprises a non-aqueous organic solvent, an additive and a lithium salt, wherein the additive comprises 1,3, 6-hexanetricarbonitrile and fluoroethylene carbonate; the 1,3, 6-hexanetricarbonitrile has a color of <150 Hazen. Further, the 1,3, 6-hexanetricarbonitrile has a chroma of 100Hazen or less, e.g. 90Hazen or less, e.g. 60Hazen or less, e.g. 30Hazen or less.

In one embodiment of the present invention, the chromaticity is measured by a platinum-cobalt colorimetric method.

In one embodiment of the invention, the 1,3, 6-hexanetricarbonitrile acts as a high voltage additive.

In one embodiment of the invention, the 1,3, 6-hexanetricarbonitrile is used in an electrolyte, wherein nitrile-CN groups can be combined with transition metals on the surface of a negative electrode, so that the deposition of transition metal ions dissolved out of a positive electrode on the negative electrode is inhibited, and the decomposition of the electrolyte on the negative electrode is inhibited.

In one embodiment of the invention, the fluoroethylene carbonate is used as a negative electrode film forming additive and can promote the negative electrode film forming.

In one embodiment of the present invention, the chromaticity of the electrolyte containing 1,3, 6-hexanetricarbonitrile increases more severely with the increase of the storage time during the storage of the electrolyte, and the storage period of the electrolyte can be prolonged by controlling the chromaticity of the material; the lithium ion battery containing the electrolyte has better high-temperature cycle and storage performance.

As described above, the present invention also provides a method for preparing the above electrolyte, the method comprising:

and mixing a nonaqueous organic solvent, a lithium salt and an additive to prepare the electrolyte.

In one embodiment of the invention, the mixing is not limited by the order of addition.

As mentioned above, the present invention also provides a lithium ion battery, which includes the above electrolyte. Furthermore, the lithium ion battery comprises a positive plate, a negative plate and a diaphragm, wherein the diaphragm is arranged between the positive plate and the negative plate. The diaphragm arranged between the positive plate and the negative plate can prevent the current short circuit caused by the contact of the two plates and can allow lithium ions to pass through.

In one aspect of the present invention, the anode includes an anode current collector and an anode active material layer disposed on one or both surfaces of the anode current collector.

Wherein, the negative current collector is selected from copper foil, such as electrolytic copper foil or rolled copper foil.

Wherein the anode active material layer includes an anode active material and an anode binder.

In some embodiments, the negative active material may be one or more of graphite, a silicon material, a silicon-carbon composite material, a silicon-oxygen material, an alloy material, and a lithium-containing metal composite oxide material.

In one aspect of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on one or both surfaces of the positive electrode current collector.

Wherein the positive electrode current collector is selected from aluminum foil.

Wherein the positive electrode active material layer includes a positive electrode active material and a positive electrode binder.

In some embodiments, the positive active material is a lithium-containing compound. The lithium-containing compound includes one or more of a lithium transition metal composite oxide and a lithium transition metal phosphate compound.

In one embodiment of the present invention, the positive electrode active material has a compacted density of 3.8 to 4.4mg/cm when coated³The negative electrode active material has a compacted density of 1.5 to 1.9mg/cm when applied³。

In one aspect of the invention, the separator is selected from porous films.

Wherein, the diaphragm is a porous film made of polymer.

The preparation method of the present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.

Example 1

(1) Preparation of positive plate

Mixing a positive electrode active material 4.4V Lithium Cobaltate (LCO), a binder polyvinylidene fluoride (PVDF) and a conductive agent acetylene black according to a weight ratio of 97:1.5:1.5, adding N-methyl pyrrolidone (NMP), and stirring under the action of a vacuum stirrer until a mixed system becomes positive electrode slurry with uniform fluidity; uniformly coating the positive electrode slurry on an aluminum foil with the thickness of 9-13 mu m; drying the coated positive plate in an oven for 4-10h, rolling and cutting to obtain the required positive plate, wherein the compaction density of the positive plate is 4.15mg/cm³。

(2) Preparation of negative plate

Mixing a negative electrode active material graphite, a thickening agent sodium carboxymethyl cellulose, a binder styrene butadiene rubber and a conductive agent according to a weight ratio of 97:1:1:1, adding deionized water, and obtaining negative electrode slurry under the action of a vacuum stirrer; uniformly coating the negative electrode slurry on a copper foil with the thickness of 6-9 mu m; drying the coated negative plate in an oven for 6-12h, then performing cold pressing and slitting to obtain the negative plate, wherein the compaction density of the negative plate is 1.75mg/cm³。

(3) Preparation of electrolyte

The electrolyte consists of a nonaqueous organic solvent, lithium salt and an additive, wherein the nonaqueous organic solvent is uniformly mixed by Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC) and Propyl Propionate (PP) in a mass ratio of 20:10:20:50, and accounts for 79 wt.% of the total mass of the nonaqueous electrolyte; the lithium salt is lithium hexafluorophosphate which accounts for 14 wt% of the total mass of the nonaqueous electrolyte; the additives used were negative film-forming additive fluoroethylene carbonate and high voltage additive 1,3, 6-hexanetricarbonitrile having a hue of 30Hazen, wherein fluoroethylene carbonate accounted for 6 wt.% of the total mass of the nonaqueous electrolyte and 1,3, 6-hexanetricarbonitrile accounted for 1 wt.% of the total mass of the nonaqueous electrolyte, to give the electrolyte for a lithium ion battery of example 1.

(4) Preparation of lithium ion battery

Stacking the prepared positive plate, the prepared isolating membrane and the prepared negative plate in sequence to ensure that the isolating membrane is positioned between the positive plate and the negative plate to play an isolating role, and then winding to obtain a naked battery cell without liquid injection; placing the bare cell in an outer packaging foil, injecting the prepared electrolyte into the dried bare cell, and performing vacuum packaging, standing, formation, shaping, sorting and other processes to obtain the required lithium ion battery.

Example 2

Unlike example 1, the high voltage additive 1,3, 6-hexanetricarbonitrile used in the preparation of the electrolyte had a color of 60Hazen and was used in an amount of 3 wt.% based on the total mass of the nonaqueous electrolyte and the nonaqueous organic solvent was used in an amount of 77 wt.% based on the total mass of the nonaqueous electrolyte. The rest is the same as in example 1.

Example 3

Unlike example 1, the high voltage additive 1,3, 6-hexanetricarbonitrile used in the preparation of the electrolyte had a color of 90Hazen and was used in an amount of 5 wt.% based on the total mass of the nonaqueous electrolyte and the nonaqueous organic solvent was used in an amount of 75 wt.% based on the total mass of the nonaqueous electrolyte. The rest is the same as in example 1.

Example 4

Unlike example 1, the lithium salt used in the preparation of the electrolyte was lithium hexafluorophosphate accounting for 16 wt.% of the total mass of the nonaqueous electrolyte, and the nonaqueous organic solvent accounted for 77 wt.% of the total mass of the nonaqueous electrolyte. The rest is the same as in example 1.

Comparative example 1

Unlike example 1, in the preparation of the electrolyte, only negative electrode film-forming additive fluoroethylene carbonate was used, which accounted for 6 wt.% of the total mass of the nonaqueous electrolyte solution, and the nonaqueous organic solvent accounted for 80 wt.% of the total mass of the nonaqueous electrolyte solution. The rest is the same as in example 1.

Comparative example 2

In contrast to example 1, the high-voltage additive 1,3, 6-hexanetricarbonitrile used in the preparation of the electrolyte had a color number of 150 Hazen. The rest is the same as in example 1.

Comparative example 3

In contrast to example 1, the high-voltage additive 1,3, 6-hexanetricarbonitrile used in the preparation of the electrolyte had a color number of 200 Hazen. The rest is the same as in example 1.

The lithium ion batteries obtained in the above comparative examples and examples were subjected to electrochemical performance tests, and the following descriptions were made:

45 ℃ cycling experiment: the batteries obtained in examples 1 to 4 and comparative examples 1 to 3 were placed in an environment of (25 +/-2) ° C, allowed to stand for 2 to 3 hours, when the battery body reached (25 +/-2) ° C, the cut-off current of the battery was 0.025C according to 1C constant current charging, allowed to stand for 5 minutes after the battery was fully charged, and then discharged to a cut-off voltage of 3.0V at a constant current of 0.7C, the maximum discharge capacity of the previous 3 cycles was recorded as an initial capacity Q, when the cycles reached the required number, the last discharge capacity Q1 of the battery was recorded, and the calculation results of the capacity retention rate are shown in table 1.

The calculation formula used therein is as follows:

capacity retention (%) ═ Q1/Q × 100%.

High temperature storage experiment: the batteries obtained in examples 1 to 4 and comparative examples 1 to 3 were subjected to a charge-discharge cycle test at room temperature for 3 times at a charge-discharge rate of 0.5C, and then a 0.5C constant current charge cutoff current was 0.025C and charged to a full charge state, and the maximum discharge capacity Q and the battery thickness T of the previous 3 0.5C cycles were recorded, respectively. The battery in a full-charge state is stored for 48 hours at 70 ℃, the thickness T0 and the discharge capacity Q1 of 0.5C after 48 hours are recorded, then the battery is charged and discharged for 3 times at the room temperature with the multiplying power of 0.5C, the maximum discharge capacity Q2 of 3 cycles is recorded, experimental data such as the thickness change rate, the capacity retention rate and the capacity recovery rate of the battery stored at high temperature are obtained through calculation, and the recording results are shown in table 1.

The calculation formula used therein is as follows:

thickness change rate (%) - (T0-T)/T × 100%;

capacity retention (%) ═ Q1/Q × 100%;

capacity recovery (%) - (-) Q2/Q.times.100%.

TABLE 1 results of the charge-discharge cycle, high-temperature storage test of examples 1 to 4 and comparative examples 1 to 3

As can be seen from the results of table 1: as can be seen from comparative example 1 and examples 1 to 4, the addition of 1,3, 6-hexanetricarbonitrile significantly improves the high-temperature cycle and storage properties of the battery, and the improvement effect becomes more significant as the amount added increases. As can be seen from comparison of example 1 with comparative examples 2 to 3, as the color of the added 1,3, 6-hexanetricarbonitrile increases, the quality of the electrolyte becomes poor, resulting in deterioration of high-temperature cycle and storage properties of the battery.

In summary, the electrolyte for the high-voltage lithium ion battery provided by the invention can significantly improve the high-temperature cycle and storage performance of the high-voltage lithium ion battery by controlling the chromaticity of 1,3, 6-hexanetricarbonitrile used in the electrolyte.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.