CN113130890B - A lithium ion battery - Google Patents

Abstract

The invention belongs to the technical field of new energy, and in particular relates to a lithium ion battery. The lithium-ion battery comprises a positive pole, a negative pole, a separator and a non-aqueous electrolyte, the positive pole comprises a positive active material, and the positive active material comprises lithium cobalt oxide; the non-aqueous electrolyte comprises the first cyclic carbonate and a second cyclic carbonate different from the first cyclic carbonate; the first cyclic carbonate is a fluorinated cyclic carbonate; the weight percentage of the first cyclic carbonate is 12% to 22%, the weight percentage of the second cyclic carbonate is less than or equal to 2%. Among them, the content of the second cyclic carbonate is reduced to a low level, which greatly reduces the degree of side reaction of the electrolyte being oxidized to produce gas, and reduces battery gas production. The first cyclic carbonate acts as a high dielectric in the electrolyte The use of a constant solvent has a better negative electrode film-forming effect than the second cyclic carbonate, and can ensure better cycle performance.

Description

A lithium ion battery

technical field

The invention belongs to the technical field of new energy sources, and in particular relates to a lithium ion battery.

Background technique

With the continuous improvement of the cruising range of new energy vehicles and the continuous development of thinner and lighter 3C digital products, the battery industry is increasingly demanding high energy density of lithium-ion batteries. Designing lithium-ion batteries with high energy density can start from the following aspects: 1) increase the gram capacity of positive electrode materials; 2) improve the battery discharge platform; 3) increase the proportion of active materials in the battery; increase the cut-off voltage of lithium-ion batteries It is one of the important ways to increase the energy density of the battery, because with the increase of the charge cut-off voltage, the positive electrode material can achieve a higher gram capacity, and the discharge platform is significantly improved. The effects of the two aspects have an immediate effect on the improvement of the energy density. Effect.

As the battery voltage gradually increases, the positive electrode material enters a higher delithiation state, the structural stability of the material will deteriorate, and the oxidation of the surface will also increase significantly. The instability of the material structure and its high oxidation are especially evident at the electrode/electrolyte interface. The specific manifestations are: the battery generates gas, the internal resistance increases rapidly, and the capacity drops sharply. The gas production of the battery will lead to an increase in internal pressure, which may further develop into dangerous situations such as explosion and combustion of the battery. Therefore, high-voltage batteries and electrolytes need to be matched.

It is well known that cyclic ethylene carbonate (EC) can provide high conductivity for the electrolyte due to its high dielectric constant, and its negative electrode film-forming solvent can ensure good cycle performance of the battery, so it is widely used in non-aqueous lithium in the secondary battery. However, the high-voltage stability of EC is poor, and it is easy to be oxidized and decomposed to produce gas on the high-voltage positive electrode, resulting in attenuation of battery performance. Propylene carbonate (PC) has better high voltage resistance, a dielectric constant comparable to EC, and a wider low-temperature liquidus temperature. It is also widely used in lithium-ion batteries. However, PC cannot produce a film-forming reaction on the negative electrode. , too much PC substitution will lead to degradation of cycle performance. Fluoroethylene carbonate (FEC) is currently widely used as an additive in high-voltage lithium-ion to ensure the cycle performance of high-voltage batteries due to its high decomposition voltage and oxidation resistance, as well as good film-forming properties. However, when FEC is used as an additive to the electrolyte of a high-voltage battery, the electrolyte is more likely to generate gas, which leads to an increase in the internal pressure of the battery during high-temperature storage and high-temperature cycling, and the battery bulges, swells, and even explodes.

Contents of the invention

The technical problem to be solved by the present invention is to provide a lithium-ion battery for the problem of gas production during high-temperature storage and high-temperature cycle of the existing high-voltage lithium-ion battery.

In order to solve the above technical problems, an embodiment of the present invention provides a lithium ion battery, including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, the positive electrode includes a positive electrode active material, and the positive electrode active material contains lithium cobalt oxide;

The non-aqueous electrolyte includes a first cyclic carbonate and a second cyclic carbonate different from the first cyclic carbonate;

The first cyclic carbonate is a fluorinated cyclic carbonate;

Based on the total weight of the non-aqueous electrolyte of the lithium-ion battery as 100%, the weight percentage of the first cyclic carbonate is 12% to 22%, and the weight percentage of the second cyclic carbonate is less than or equal to 2 %.

Optionally, the first cyclic carbonate includes fluoroethylene carbonate; the second cyclic carbonate is a non-fluorine substituted or unsubstituted cyclic carbonate.

Optionally, the unsubstituted cyclic carbonate is a cyclic carbonate with 1-10 carbon atoms.

Optionally, the non-fluorine-substituted cyclic carbonate is a cyclic carbonate substituted by a cyano group, an oxygen-containing hydrocarbon group, a silicon-containing hydrocarbon group, an alkyl group, an ether group, or a sulfur-containing hydrocarbon group.

Optionally, the surface of the positive electrode active material is coated with metal oxide or doped with other elements inside; the metal oxide is magnesium oxide and/or aluminum oxide; the doped element is selected from Li, K, One or more of Mg, Ca, Al, Cr, Cu, Ni, Ti, Nd, B and P.

Optionally, the charging cut-off voltage of the lithium-ion battery is 4.35V or above.

Optionally, based on 100% of the total weight of the lithium-ion battery non-aqueous electrolyte, the weight percentage of the first cyclic carbonate in the non-aqueous electrolyte is 14% to 20%, and the second ring The weight percentage of the carbonic acid ester in the non-aqueous electrolyte solution is less than or equal to 0.5%.

Optionally, the first cyclic carbonate includes fluoroethylene carbonate; the second cyclic carbonate is a non-fluorine substituted or unsubstituted cyclic carbonate.

Optionally, the second cyclic carbonate includes ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate , one or more of -2,3-pentylene carbonate.

Optionally, the non-aqueous electrolyte also includes linear carbonate and/or carboxylate, and the total weight of the lithium-ion battery non-aqueous electrolyte is 100%, and the carboxylate and/or the The linear carbonate accounts for 50% to 65% of the total weight percentage of the non-aqueous electrolytic solution.

Optionally, the linear carbonate includes one or more of diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and ethylene propyl carbonate;

The carboxylic acid ester includes ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone One or more of lactone and ε-caprolactone.

Optionally, the non-aqueous electrolyte also includes additives, and the weight percentage of the additives is 1-20% based on 100% of the total weight of the lithium-ion battery non-aqueous electrolyte;

The additive includes one or more of vinylene carbonate, 1,3-propane sultone, dinitrile compounds, and trinitrile compounds;

The dinitrile compound includes one or more of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile, sebaconitrile, and the lithium ion battery is not Based on the total weight of the water electrolytic solution as 100%, the weight percentage of the dinitrile compound is 0.1%-10%; the weight percentage of the 1,3-propane sultone is 1-10%.

Optionally, the non-aqueous electrolytic solution also includes a lithium salt, and the lithium salt includes lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(trifluoromethylsulfonyl)imide and one or more of lithium salts of bisfluorosulfonimide, and the concentration of the lithium salts is 0.1M-2M.

In the lithium ion battery provided by the embodiment of the present invention, the positive electrode material includes lithium cobalt oxide, and its surface can catalyze the in-situ film-forming reaction of fluoroethylene carbonate to play a protective role. In the non-aqueous electrolyte, the first The content of cyclic carbonate fluorinated cyclic carbonate makes it used as a high dielectric constant solvent in the electrolyte, and the content of the second cyclic carbonate is reduced to a lower level, so that the electrolyte is oxidized to produce gas The degree of side reactions is greatly reduced, reducing battery gas production and improving high-temperature storage performance. Moreover, the fluorinated cyclic carbonate has a better negative electrode film-forming effect than the second cyclic carbonate, and can ensure better cycle performance.

detailed description

In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

A lithium-ion battery provided in an embodiment of the present invention includes a positive electrode, a negative electrode, a diaphragm, and a non-aqueous electrolyte, the positive electrode includes a positive electrode active material, and the positive electrode active material includes lithium cobalt oxide;

The negative electrode includes a negative electrode active material, and the negative electrode active material includes one or more of hard carbon, soft carbon, graphite, and silicon-containing materials.

In some embodiments, the separator is separated between the positive electrode of the battery and the negative electrode of the battery, and the separator is a conventional separator in the field of lithium-ion batteries, which will not be repeated here.

The non-aqueous electrolyte comprises a first cyclic carbonate and a second cyclic carbonate different from the first cyclic carbonate; the first cyclic carbonate is a fluorinated cyclic carbonate; Based on the total weight of the non-aqueous electrolyte of the lithium ion battery as 100%, the weight percentage of the first cyclic carbonate is 12%-22%, and the weight percentage of the second cyclic carbonate is less than or equal to 2%.

Traditionally, in an electrolyte that uses a second cyclic carbonate (such as EC, PC) as a high dielectric constant solvent, the second cyclic carbonate generally accounts for 10% to 30% by weight of the electrolyte, and the first cyclic carbonate Ester fluorinated cyclic carbonate (such as FEC) is usually added in a small amount (less than 10%) as an optional negative electrode film-forming additive, and although the first cyclic carbonate can improve the cycle performance, it will cause obvious gas production and affect the battery life. High temperature storage performance.

The inventor has found through a large number of experimental analysis that the lithium battery system using lithium cobaltate as the positive electrode active material has the problem of high-temperature storage and gas production. When the first cyclic carbonate fluorinated cyclic carbonate (such as FEC) is used as a high dielectric constant solvent, and the content of the second cyclic carbonate different from the first cyclic carbonate is reduced to a lower level , the lithium-ion battery using the non-aqueous electrolyte exhibits excellent high-temperature storage performance, does not produce gas and has good capacity retention and recovery performance, and the battery has good cycle performance.

In one embodiment, the surface of the positive electrode active material is coated with metal oxide or doped with other elements inside; the metal oxide is magnesium oxide and/or aluminum oxide; the doped element is selected from Li, One or more of K, Mg, Ca, Al, Cr, Cu, Ni, Ti, Nd, B and P.

In one embodiment, the charging cut-off voltage of the lithium-ion battery is 4.35V or above, and in a preferred embodiment of the present invention, the charging cut-off voltage is 4.45V.

In one embodiment, based on 100% of the total weight of the non-aqueous electrolyte of the lithium-ion battery, the weight percentage of the first cyclic carbonate in the non-aqueous electrolyte is 14% to 20%, specifically, The weight percent of the first cyclic carbonate can be 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20% %. The weight percentage of the second cyclic carbonate in the non-aqueous electrolyte is less than or equal to 0.5%.

The content of the second cyclic carbonate is reduced to a certain level, and the first cyclic carbonate fluorinated cyclic carbonate is used as a high dielectric constant solvent in the electrolyte, and the non-aqueous electrolyte is oxidized to generate gas. The degree is greatly reduced, reducing gas production. More preferably, when the weight ratio of the second cyclic carbonate is 0, the electrolyte produces very little gas and exhibits excellent high-temperature storage performance.

In one embodiment, the first cyclic carbonate includes fluoroethylene carbonate; the second cyclic carbonate is a non-fluorine substituted or unsubstituted cyclic carbonate.

In one embodiment, the unsubstituted cyclic carbonate is a cyclic carbonate with 1-10 carbon atoms, and the non-fluorine substituted cyclic carbonate is a cyano group, an oxygen-containing hydrocarbon group, a silicon-containing Cyclic carbonates substituted by hydrocarbon groups, alkyl groups, ether groups, and sulfur-containing hydrocarbon groups.

In one embodiment, the second cyclic carbonate includes ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-butylene carbonate, One or more of pentyl ester and 2,3-pentylene carbonate.

It should be noted that the above compounds are part of the compounds claimed in the present invention, but not limited thereto, and should not be construed as limiting the present invention.

In one embodiment, the non-aqueous electrolytic solution also includes linear carbonate and/or carboxylate, and a mixed solution of low-viscosity carboxylate organic solvent and chain carbonate organic solvent is used as the lithium-ion battery. The solvent of the nonaqueous electrolytic solution can reduce the viscosity of the nonaqueous electrolytic solution.

Based on the total weight of the non-aqueous electrolyte of the lithium-ion battery as 100%, the total weight percentage of the carboxylate and/or the linear carbonate in the non-aqueous electrolyte is 50% to 65%, specifically , the sum of the weight ratio of the carboxylate and the linear carbonate can be 50%, 52%, 54%, 55%, 56%, 58%, 60%, 62%, 64%, 65%.

In one embodiment, the linear carbonate includes one or more of diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and ethylene propyl carbonate.

In one embodiment, the carboxylic acid ester includes ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-hexyl One or more of lactone, σ-valerolactone and ε-caprolactone.

In one embodiment, the non-aqueous electrolyte also includes additives, and the weight percentage of the additives is 1-20% based on 100% of the total weight of the lithium-ion battery non-aqueous electrolyte; the additives include One or more of vinylene carbonate, 1,3-propane sultone, dinitrile compounds, and trinitrile compounds.

The dinitrile compound includes one or more of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile, sebaconitrile, and the lithium ion battery is not Based on the total weight of the water electrolytic solution as 100%, the weight percentage of the dinitrile compound is 0.1%-10%; the weight percentage of the 1,3-propane sultone is 1-10%.

It should be noted that the above compounds are part of the compounds claimed in the present invention, but not limited thereto, and should not be construed as limiting the present invention.

In the scheme of the present invention, there is no special limitation on the lithium salt, and various existing substances can be used.

In one embodiment, the lithium salt includes lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(trifluoromethylsulfonyl)imide and lithium salt of bisfluorosulfonylimide One or more of them, and the lithium salt concentration is 0.1M-2M, preferably 0.8M-1.5M.

The present invention is further described by way of examples below.

Example 1

1) Preparation of non-aqueous electrolyte

Mix 35% diethyl carbonate (DEC) and 28% propyl propionate (PP), add 22% fluoroethylene carbonate (FEC), and then add 15% lithium hexafluorophosphate ( LiPF ₆ ).

2) Preparation of positive plate

Mix positive active material lithium cobaltate (LiCoO ₂ ), conductive carbon black Super-P and binder polyvinylidene fluoride (PVDF) at a mass ratio of 93:4:3, and then disperse them in N-methyl- 2-pyrrolidone (NMP) to obtain positive electrode slurry. The slurry is uniformly coated on both sides of the aluminum foil, dried, calendered and vacuum-dried, and an aluminum lead-out wire is welded by an ultrasonic welder to obtain a positive plate.

3) Preparation of negative plate

Mix negative electrode active material artificial graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) according to the mass ratio of 94:1:2.5:2.5, and then disperse them in the deionized water to obtain negative electrode slurry. The slurry is coated on both sides of the copper foil, dried, calendered and vacuum dried, and a nickel lead-out wire is welded by an ultrasonic welder to obtain a negative plate.

4) Preparation of batteries

A polyethylene microporous membrane with a thickness of 20 μm is placed between the positive plate and the negative plate as a separator, and then the sandwich structure composed of the positive plate, negative plate and separator is wound, and then the wound body is flattened and placed in an aluminum plastic film packaging bag, and then baked at 85°C for 24 hours to obtain the cell to be filled with liquid.

5) Injection and formation of batteries

In a glove box with a dew point controlled below -40°C, inject the non-aqueous electrolyte solution prepared above into the battery cell, and the amount of the electrolyte solution should ensure that the gaps in the battery core are filled. Then carry out the formation according to the following steps: 0.05C constant current charging for 180min, 0.1C constant current charging for 240min, vacuum shaping and sealing after shelving for 1hr, and then further charging with a constant current of 0.2C to 4.45V, after 24hr at room temperature, charging at 0.2C The current constant current discharge to 3.0V.

Example 2

Identical with the technique of embodiment 1, as shown in table 1, difference is:

In the preparation step of the non-aqueous electrolytic solution, based on the total weight of the non-aqueous electrolytic solution as 100%, 33% propyl propionate (PP) is added to the non-aqueous electrolytic solution, and 12% fluorinated Ethylene carbonate (FEC). Besides, on the basis of Example 1, 3% by weight of 1,3-propane sultone (1,3-PS) and 2% of succinonitrile (SN) were added as additives.

Example 3

Identical with the technique of embodiment 1, as shown in table 1, difference is:

In the preparation step of the non-aqueous electrolytic solution, based on the total weight of the non-aqueous electrolytic solution as 100%, 30% propyl propionate (PP) is added to the non-aqueous electrolytic solution, and 15% fluorinated Ethylene carbonate (FEC). Besides, on the basis of Example 1, 3% by weight of 1,3-propane sultone (1,3-PS) and 2% of succinonitrile (SN) were added as additives.

Example 4

Identical with the technique of embodiment 1, as shown in table 1, difference is:

In the preparation step of the non-aqueous electrolytic solution, 29% propyl propionate (PP) is added to the non-aqueous electrolytic solution based on the total weight of the non-aqueous electrolytic solution, and 15% fluorinated Ethylene carbonate (FEC), in addition, on the basis of embodiment 1, adding weight is 1% ethylene carbonate (EC), weight is 3% 1,3-propane sultone ( 1,3-PS) and 2% succinonitrile (SN).

Example 5

Identical with the technique of embodiment 1, as shown in table 1, difference is:

In the preparation step of the non-aqueous electrolytic solution, 29% propyl propionate (PP) is added to the non-aqueous electrolytic solution based on the total weight of the non-aqueous electrolytic solution, and 15% fluorinated Ethylene carbonate (FEC), in addition, on the basis of embodiment 1, add weight and be 1% propylene carbonate (PC), 3% 1,3-propane sultone (1,3- PS) and 2% succinonitrile (SN).

Example 6

Identical with the technique of embodiment 1, as shown in table 1, difference is:

In the preparation step of the non-aqueous electrolytic solution, 29% propyl propionate (PP) is added to the non-aqueous electrolytic solution based on the total weight of the non-aqueous electrolytic solution, and 15% fluorinated Ethylene carbonate (FEC), in addition, on the basis of embodiment 1, add weight and be 0.5% ethylene carbonate (EC), 0.5% propylene carbonate (PC), 3% 1,3- Propane sultone (1,3-PS) and 2% succinonitrile (SN).

Example 7

Identical with the technique of embodiment 1, as shown in table 1, difference is:

In the preparation step of the non-aqueous electrolytic solution, based on the total weight of the non-aqueous electrolytic solution as 100%, 23% propyl propionate (PP) was added to the non-aqueous electrolytic solution, and 22% fluorinated Ethylene carbonate (FEC), in addition, on the basis of embodiment 1, add weight again and be 3% 1,3-propane sultone (1,3-PS) and 2% succinonitrile (SN) as an additive.

Comparative example 1

Identical with the technique of embodiment 1, as shown in table 1, difference is:

In the preparation step of the non-aqueous electrolytic solution, based on the total weight of the non-aqueous electrolytic solution as 100%, 28% propyl propionate (PP) was added to the non-aqueous electrolytic solution, and 5% fluorinated Ethylene carbonate (FEC), in addition, on the basis of embodiment 1, add 12% ethylene carbonate (EC) and 5% propylene carbonate (PC) by weight.

Comparative example 2

Identical with the technique of embodiment 1, as shown in table 1, difference is:

In the preparation step of the non-aqueous electrolytic solution, 23% propyl propionate (PP) is added to the non-aqueous electrolytic solution based on the total weight of the non-aqueous electrolytic solution, and 5% fluorinated Ethylene carbonate (FEC), in addition, on the basis of embodiment 1, add weight and be 12% ethylene carbonate (EC) and 5% propylene carbonate (PC), and 3% 1,3 - Propane sultone (1,3-PS) and 2% of succinonitrile (SN).

Comparative example 3

Identical with the technique of embodiment 1, as shown in table 1, difference is:

In the preparation step of the non-aqueous electrolytic solution, 37% propyl propionate (PP) is added to the non-aqueous electrolytic solution, and 8% fluorinated Ethylene carbonate (FEC), in addition, on the basis of embodiment 1, add weight again and be 3% 1,3-propane sultone (1,3-PS) and 2% succinonitrile (SN) as an additive.

Comparative example 4

Identical with the technique of embodiment 1, as shown in table 1, difference is:

In the preparation step of the non-aqueous electrolytic solution, based on the total weight of the non-aqueous electrolytic solution as 100%, 20% propyl propionate (PP) is added to the non-aqueous electrolytic solution, and 25% fluorinated Ethylene carbonate (FEC), in addition, on the basis of embodiment 1, add weight again and be 3% 1,3-propane sultone (1,3-PS) and 2% succinonitrile (SN) as an additive.

Comparative example 5

Identical with the technique of embodiment 1, as shown in table 1, difference is:

In the preparation step of the non-aqueous electrolytic solution, based on the total weight of the non-aqueous electrolytic solution as 100%, 25% propyl propionate (PP) is added to the non-aqueous electrolytic solution, and 15% of Ethylene carbonate (FEC), in addition, on the basis of Example 1, add 5% ethylene carbonate (EC), 3% 1,3-propane sultone (1,3-PS) and 2% succinonitrile (SN).

Comparative example 6

Identical with the technique of embodiment 1, as shown in table 1, difference is:

In the preparation step of the non-aqueous electrolytic solution, based on the total weight of the non-aqueous electrolytic solution as 100%, 25% propyl propionate (PP) is added to the non-aqueous electrolytic solution, and 15% of Ethylene carbonate (FEC), in addition, on the basis of embodiment 1, add weight again and be 5% propylene carbonate (PC), and 3% 1,3-propane sultone (1,3 -PS) and 2% succinonitrile (SN).

Comparative example 7

Identical with the technique of embodiment 1, as shown in table 1, difference is:

In the preparation step of the non-aqueous electrolytic solution, based on the total weight of the non-aqueous electrolytic solution as 100%, 25% propyl propionate (PP) is added to the non-aqueous electrolytic solution, and 15% of Ethylene carbonate (FEC), in addition, on the basis of embodiment 1, add weight and be 2% ethylene carbonate (EC), 3% propylene carbonate (PC), and 3% 1,3 - Propane sultone (1,3-PS) and 2% of succinonitrile (SN).

Comparative example 8

Identical with the technique of embodiment 1, as shown in table 1, difference is:

In the preparation step of the non-aqueous electrolytic solution, based on the total weight of the non-aqueous electrolytic solution as 100%, 28% propyl propionate (PP) was added to the non-aqueous electrolytic solution, and 22% fluorinated Ethylene carbonate (FEC).

In the preparation step of the positive electrode plate, NCM111 is used as the positive electrode active material.

Table 1 shows the dosage of each component of the electrolyte solvent in the above examples and comparative examples.

The consumption of each component of table 1 electrolyte solvent (percentage by weight)

EC PC FEC DEC PP LiPF6 1,3-PS SN positive active material Comparative example 1 12 5 5 35 28 15 LiCoO₂ Comparative example 2 12 5 5 35 twenty three 15 3 2 LiCoO₂ Comparative example 3 8 35 37 15 3 2 LiCoO₂ Comparative example 4 25 35 20 15 3 2 LiCoO₂ Comparative example 5 5 15 35 25 15 3 2 LiCoO₂ Comparative example 6 5 15 35 25 15 3 2 LiCoO₂ Comparative example 7 2 3 15 35 25 15 3 2 LiCoO₂ Comparative example 8 twenty two 35 28 15 NCM111 Example 1 twenty two 35 28 15 LiCoO₂ Example 2 12 35 33 15 3 2 LiCoO₂ Example 3 15 35 30 15 3 2 LiCoO₂ Example 4 1 15 35 29 15 3 2 LiCoO₂ Example 5 1 15 35 29 15 3 2 LiCoO₂ Example 6 0.5 0.5 15 35 29 15 3 2 LiCoO₂ Example 7 twenty two 35 twenty three 15 3 2 LiCoO₂

Performance Testing

The following performance tests were carried out on the lithium-ion batteries prepared in the above-mentioned Examples 1-7 and Comparative Examples 1-8

1) High temperature cycle performance test

Put the battery in an oven with a constant temperature of 45°C, charge it with a constant current of 1C to 4.45V, then charge it with a constant voltage until the current drops to 0.03C, and then discharge it with a constant current of 1C to 3.0V, and cycle 300 times in this way, record The discharge capacity of the first cycle and the discharge capacity of the 300th cycle were calculated to calculate the capacity retention rate of the high-temperature cycle to evaluate its high-temperature cycle performance.

The calculation formula of capacity retention rate is as follows:

Capacity retention rate (%) = discharge capacity of the 300th cycle / discharge capacity of the 1st cycle × 100%

2) High temperature storage performance test

Charge the formed battery to 4.45V with 0.5C constant current and constant voltage at room temperature, measure the initial discharge capacity and initial battery thickness of the battery, and then store it at 60°C for 21 days, wait for the battery to cool to room temperature and then measure the final thickness of the battery, calculate Battery thickness expansion rate; then discharge at 0.3C to 3V to measure the holding capacity and recovery capacity of the battery. Calculated as follows:

Battery capacity retention rate (%) = retention capacity/initial capacity × 100%;

Battery capacity recovery rate (%) = recovery capacity / initial capacity × 100%;

Battery thickness expansion rate (%)=(final thickness-initial thickness)/initial thickness×100%.

3) High temperature storage performance test

Charge the formed battery to 4.45V with 0.5C constant current and constant voltage at room temperature, measure the initial discharge capacity and initial battery thickness of the battery, and then store it at 85°C for 6 hours, wait for the battery to cool to room temperature and then measure the final thickness of the battery. Calculate the thickness expansion rate of the battery; then discharge it at 0.3C to 3V to measure the holding capacity and recovery capacity of the battery. Calculated as follows:

Battery capacity retention rate (%) = retention capacity/initial capacity × 100%;

Battery capacity recovery rate (%) = recovery capacity / initial capacity × 100%;

Battery thickness expansion rate (%)=(final thickness-initial thickness)/initial thickness×100%.

Fill in the calculated test results in Table 2.

Table 2

Comparing Example 1 with Comparative Example 1, it shows that the electrolyte solution whose FEC content is in the range of 12%-22% and the total content of EC and PC is less than 2% by weight of the electrolyte solution has better high-temperature storage performance and high-temperature cycle performance, In particular, the problem of gas production can be significantly improved, and the volume expansion rate is significantly reduced.

Comparing Example 1 and Comparative Example 8, it shows that the FEC content is in the range of 12%-22% and the total content of EC and PC is lower than 2% of the weight of the electrolyte. The electrolyte matches the high voltage lithium cobaltate positive electrode material ratio and matches the NMC111 positive electrode The material has better storage performance, which may be because FEC can be catalyzed to form a film on the surface of lithium cobaltate positive electrode and prevent further reactions, but the film-forming reaction cannot occur on NMC111.

The comparison between Examples 2-7 and Comparative Example 2 shows that when the FEC content in the electrolyte is in the range of 12%-22% and the total content of EC and PC is less than 2% by weight of the electrolyte, the high-temperature storage performance of the battery is especially good. The swelling improvement is particularly obvious, and the high-temperature cycle performance is also significantly improved.

Comparing Examples 2, 3, and 7 with Comparative Examples 3-4, it shows that when the FEC is between 12%-22% and the total content of EC and PC is less than 1%, the battery can have better high-temperature storage and cycle performance, and The FEC content is preferably 14% to 20%. When the FEC content is less than 12% and the total content of EC and PC is less than 2%, although the battery has good high-temperature storage performance, the high-temperature cycle performance is poor, and the phenomenon of cycle diving occurs. The reason may be: high dielectric strength in the electrolyte Too little solvent content in the electrical constant leads to too low conductivity of the electrolyte. During the cycle, the continuous consumption of FEC will further reduce the conductivity, which leads to an increasing polarization of the potential of the positive and negative electrodes when the battery is charged and discharged. It will soon reach the cut-off voltage of charging and discharging, and the capacity cannot be normally exerted. What is more serious is that after the negative electrode is polarized so much that its potential is lower than the lithium analysis potential, the negative electrode will decompose lithium and cyclically dive. The reason why the FEC content cannot be greater than 22%: When the FEC content is greater than 22% and the total content of EC and PC is less than 2%, the high-temperature cycle performance of the battery has no obvious effect, indicating that the conductivity and negative electrode film-forming protection are sufficient, but high temperature However, the storage performance also began to deteriorate. The reason is still unclear. It is speculated that the stability of the solvation structure formed by too much FEC and LiPF6 deteriorates, causing the electrolyte to decompose.

Comparing Example 7 with Example 1, it shows that adding 1,3-PS and dinitrile compound SN to the electrolyte solution with FEC between 12% and 22% and the total content of EC and PC less than 2%, the battery's High-temperature storage and high-temperature cycle performance are more significantly improved.

Comparing Examples 3-6 with Comparative Examples 5-7, it shows that when the FEC in the electrolyte is between 12%-22%, the total content of EC and PC must be less than 2%, so that the battery can have good storage without gas production performance, and preserve better cycle performance, the reason is unclear.

Compared with Comparative Examples 1-2, in the conventional EC+PC solvent electrolyte, adding 1,3-PS and nitrile additive SN is more conducive to improving the storage and cycle performance of the battery.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (7)

1. a lithium ion battery, comprising positive pole, negative pole, diaphragm and non-aqueous electrolyte, is characterized in that, The positive electrode includes a positive electrode active material, and the positive electrode active material is LiCO _{O 2} ; The non-aqueous electrolyte includes a first cyclic carbonate and a second cyclic carbonate different from the first cyclic carbonate; The first cyclic carbonate is a fluorinated cyclic carbonate; Based on the total weight of the non-aqueous electrolyte of the lithium-ion battery as 100%, the weight percentage of the first cyclic carbonate is 12% to 22%, and the weight percentage of the second cyclic carbonate is less than or equal to 2 %; The first cyclic carbonate comprises fluoroethylene carbonate; The second cyclic carbonate is a non-fluorine-substituted or unsubstituted saturated cyclic carbonate; The second cyclic carbonate is selected from ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, carbonic acid - one or more components of 2,3-pentylene ester; The charging cut-off voltage of the lithium ion battery is 4.45V or above. 2. The lithium ion battery as claimed in claim 1, wherein the surface of the positive electrode active material is coated with metal oxide or internally doped with other elements; the metal oxide is magnesium oxide and/or aluminum oxide ; The doping element is selected from one or more of Li, K, Mg, Ca, Al, Cr, Cu, Ni, Ti, Nd, B and P. 3. The lithium-ion battery as claimed in claim 1 or 2, wherein the total weight of the non-aqueous electrolyte of the lithium-ion battery is 100%, and the first cyclic carbonate accounts for 100% of the non-aqueous electrolyte. The weight percentage of the non-aqueous electrolyte is 14%-20%, and the weight percentage of the second cyclic carbonate in the non-aqueous electrolyte is less than or equal to 0.5%. 4. Lithium-ion battery as claimed in claim 1, is characterized in that, described non-aqueous electrolytic solution also comprises linear carbonate and/or carboxylate, is 100% with the gross weight of described lithium-ion battery non-aqueous electrolytic solution. %, the total weight percentage of the carboxylic acid ester and/or the linear carbonate in the non-aqueous electrolyte solution is 50% to 65%. 5. lithium ion battery as claimed in claim 4, is characterized in that, described linear carbonate comprises one in diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and ethyl propyl carbonate one or more kinds; The carboxylic acid ester includes ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone One or more of lactone and ε-caprolactone. 6. The lithium-ion battery as claimed in claim 1, wherein the non-aqueous electrolyte also includes an additive, and the weight of the additive is 100% based on the total weight of the non-aqueous electrolyte of the lithium-ion battery. The percentage is 1-20%; The additive includes one or more of vinylene carbonate, 1,3-propane sultone, dinitrile compounds, and trinitrile compounds; The dinitrile compound includes one or more of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile, sebaconitrile, and the lithium ion battery is not Based on the total weight of the water electrolytic solution as 100%, the weight percentage of the dinitrile compound is 0.1%-10%; the weight percentage of the 1,3-propane sultone is 1-10%. 7. The lithium ion battery according to claim 1, wherein the non-aqueous electrolytic solution also includes a lithium salt, and the lithium salt includes lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorooxalate borate , one or more of lithium bis(trifluoromethylsulfonyl)imide and lithium bisfluorosulfonylimide, and the concentration of the lithium salt is 0.1M-2M.