Non-aqueous electrolyte and lithium ion battery

Abstract

The invention relates to a non-aqueous electrolyte and a lithium ion battery. In order to improve the cycle performance and the heat resistance of the lithium ion battery, the non-aqueous electrolyte provided by the invention comprises a lithium salt, an organic solvent and an additive, and the additive comprises 1, 2, 3, 4, 5-penta (2-cyanoethoxy) pentane and 4-methyl ethylene sulfate. According to the non-aqueous electrolyte disclosed by the invention, the cycle performance and the heat resistance of the lithium ion battery are effectively improved by compounding the 1, 2, 3, 4, 5-penta (2-cyanoethoxy) pentane and the 4-methyl ethylene sulfate.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a non-aqueous electrolyte and a lithium ion battery. Background Art

[0002] In recent years, the development of battery technology has improved rapidly. The vast market has provided more development opportunities, but also brought greater challenges. The widespread use of batteries has put forward higher requirements for the adaptability of battery usage environments. The market needs batteries to maintain good performance under different harsh environments, and a larger temperature range has become an important topic in the development of batteries. To solve this problem, more progress needs to be made in battery materials.

[0003] Due to the advantages of large energy density, high output power, and low environmental pollution, lithium ion secondary batteries are widely used in electric vehicles and consumer electronic products. To further improve the energy density of lithium ion batteries, on the one hand, the specific capacity of the positive and negative electrode materials is increased, and on the other hand, the compaction density of the negative electrode film is increased. However, when the compaction density of the negative electrode film is increased, the lithium ion battery shows a phenomenon of reduced cycle life. Therefore, it is necessary to improve the performance of lithium ion batteries when the compaction density of the negative electrode film is increased. Summary of the Invention

[0004] The purpose of the present invention is to provide a non-aqueous electrolyte and a lithium ion battery with better cycle performance and heat resistance.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A non-aqueous electrolyte includes a lithium salt, an organic solvent, and an additive. The additive includes 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 4-methyl vinyl sulfate.

[0007] When the compaction density of the positive and / or negative electrode film is increased, the wettability between the electrode sheet and the electrolyte becomes poor, and the diffusion of lithium ions is difficult, which will lead to a reduction in the cycle life of the lithium ion battery. The non-aqueous electrolyte provided by the present invention includes a compound capable of forming a lithium ion solvation and an additive that forms a protective film on the surfaces of the positive and negative electrodes. When the compaction density of the positive and / or negative electrode film is increased, the non-aqueous electrolyte provided by the present invention can have better wettability with the electrode sheet, which is conducive to the diffusion of lithium ions, thereby improving the cycle life and high temperature resistance of the lithium ion battery.

[0008] Preferably, the additive accounts for 0.1% - 10% of the total mass of the non-aqueous electrolyte.

[0009] More preferably, the additive accounts for 0.1% - 6% of the total mass of the non-aqueous electrolyte.

[0010] More preferably, the additive accounts for 0.2% to 3.5% of the total mass of the non-aqueous electrolyte.

[0011] In some embodiments, 1,2,3,4,5-penta(2-cyanoethoxy)pentane accounts for 0.1% to 1.5% of the total mass of the non-aqueous electrolyte.

[0012] In some embodiments, vinylene sulfate 4-methyl accounts for 0.5% to 2% of the total mass of the electrolyte.

[0013] Preferably, the lithium salt includes a first lithium salt and a second lithium salt. The first lithium salt is selected from one or more of lithium hexafluorophosphate, lithium difluoro(oxalato)phosphate, lithium difluorophosphate, and lithium tetrafluoro(oxalato)phosphate. The second lithium salt is selected from one or more of lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate.

[0014] In some embodiments, the first lithium salt is lithium hexafluorophosphate and the second lithium salt is lithium difluoro(oxalato)borate.

[0015] Preferably, the lithium salt accounts for 5% to 20% of the total mass of the non-aqueous electrolyte.

[0016] More preferably, the lithium salt accounts for 10% to 15% of the total mass of the non-aqueous electrolyte.

[0017] Preferably, the mass ratio of the first lithium salt to the second lithium salt is (20 to 30):1.

[0018] More preferably, the mass ratio of the first lithium salt to the second lithium salt is (22 to 26):1.

[0019] Preferably, the organic solvent includes cyclic carbonates and linear carbonates. The cyclic carbonates account for 30% to 50% of the total mass of the organic solvent.

[0020] More preferably, the cyclic carbonates include one or more of ethylene carbonate and propylene carbonate.

[0021] More preferably, the linear carbonates include one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0022] The present invention also provides a lithium ion battery, including a positive electrode sheet, a negative electrode sheet, and a separator. The lithium ion battery further includes the non-aqueous electrolyte as described above.

[0023] Preferably, the compaction density of the negative electrode sheet is 1.45 to 1.65 g / cm 3 .

[0024] More preferably, the active material in the negative electrode sheet includes graphite.

[0025] Preferably, the active material in the positive electrode sheet includes lithium iron phosphate.

[0026] More preferably, the tap density of the positive electrode sheet is 2-2.5 g / cm 3 .

[0027] The non-aqueous electrolyte of the present invention, through the synergistic effect of additives, organic solvents and lithium salts, enables better wettability between the electrolyte and the electrode sheet, and improves the diffusion ability of lithium ions. Therefore, the lithium ion battery has better cycle performance and high temperature resistance performance.

[0028] The lithium ion battery provided by the present invention has better cycle performance and heat resistance performance, can meet the increasing requirements for lithium ion batteries in fields such as new energy vehicles, and has good market prospects and economic benefits.

[0029] Due to the application of the above technical solutions, the present invention has the following advantages compared with the prior art:

[0030] The non-aqueous electrolyte of the present invention, through the compounding of 1,2,3,4,5-penta(2-cyanoethoxy)pentane and vinylene methyl sulfate, effectively improves the cycle performance and heat resistance performance of the lithium ion battery. Specific Embodiments

[0031] The present invention will be further described below in conjunction with embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions adopted in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in each implementation manner of the present invention can be combined with each other as long as they do not conflict with each other.

[0032] Unless otherwise specified, in the specific embodiments or comparative examples of the present invention, the raw materials used can be obtained through commercial channels. In the specific embodiments and comparative examples of the present invention, lithium iron phosphate batteries are taken as examples. Lithium iron phosphate batteries have characteristics such as high cycle life, good safety and low price. Therefore, lithium iron phosphate is one of the most commonly used positive electrode materials for power batteries at present.

[0033] Preparation of non-aqueous electrolyte:

[0034] In a glove box filled with argon (H2O content < 10 ppm), one or both of dimethyl carbonate (DMC) and diethyl carbonate (DEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) are mixed evenly in different mass ratios. A certain proportion of lithium difluorooxalate borate (LiODFB) and lithium hexafluorophosphate (LiPF6) are added to the mixed solution to prepare an electrolyte. Different contents of various additives are added to the electrolyte as comparative examples or embodiments.

[0035] Preparation of Lithium-ion Battery:

[0036] Positive electrode: 95 wt% of active material lithium iron phosphate, 3 wt% of acetylene black as conductive material, and 2 wt% of polyvinylidene fluoride (PVDF) as binder material are mixed in N-methylpyrrolidone solvent using a dispersion mixer to prepare a slurry. After uniformly coating both sides of the aluminum foil with the slurry and drying, it is pressed to produce the positive electrode, and the tap density of the positive electrode is 2.3 g / cm 3 .

[0037] Negative electrode: 95 wt% of active material artificial graphite, 2 wt% of conductive carbon black (SP) as conductive material, and 3 wt% of sodium carboxymethyl cellulose (CMC) as binder material are mixed using a dispersion mixer to prepare a slurry. After uniformly coating both sides of the copper foil with the slurry and drying, it is pressed to produce the negative electrode, and the tap density of the negative electrode is 1.6 g / cm 3 .

[0038] The above positive electrode, negative electrode, and polyolefin separator are laminated in the order of positive electrode, separator, and negative electrode, and wrapped with an aluminum film to obtain a battery element. After injecting the electrolyte, it is vacuum-sealed to manufacture a non-aqueous electrolyte lithium-ion battery.

[0039] Evaluation of Non-aqueous Electrolyte Lithium-ion Battery:

[0040] Battery room temperature test: The positive electrode uses lithium iron phosphate. The assembled battery is first formed. The formation conditions are: constant current charging at 0.1C to 3.7V, and finally constant voltage charging at 3.7V for 2h, standing for 10min, and then constant current discharging at 0.2C to 2.75V. Under the condition of room temperature 25°C, constant current charging at 1C to 3.75V, then constant voltage charging at 3.75V for 2h, standing for 10min, and constant current discharging at 1C to 2.75V. Record the first week discharge capacity as W1 and stand for 10min. The number of cycles is set to 2000 weeks, and the 2000th week discharge capacity is recorded as W 2000 . The 2000th week capacity retention rate = W 2000 / W1 × 100%.

[0041] High-temperature test of battery: The assembled battery is first formed under the following conditions: constant current charging at 0.1C to 3.75V, followed by constant voltage charging at 3.75V for 2h, standing for 10min, and then constant current discharging at 0.2C to 2.75V. The test conditions for the high-temperature cycling performance of lithium-ion batteries are as follows: at a high temperature of 45°C, constant current charging at 1C to 3.75V, then constant voltage charging at 3.75V for 2h, standing for 10min, constant current discharging at 1C to 2.75V. Record the discharge capacity in the first week as W1 and stand for 10min. The number of cycles is set to 1000 weeks, and the discharge capacity in the 1000th week is recorded as W 1000 . The capacity retention rate in the 1000th week = W 1000 / W1 × 100%.

[0042] In each example and comparative example, the formulation of the non-aqueous electrolyte and the capacity retention rate (%) after 2000 cycles at 25°C and the capacity retention rate (%) after 1000 cycles at 45°C are shown in Table 1.

[0043] Table 1

[0044]

[0045]

[0046] Among them, taking Example 1 as an example, the organic solvents DMC / EC / EMC = 10 / 50 / 40 means that the mass ratio of DMC, EC, and EMC is 10:50:40; the lithium salt 0.5% LiODFB + 12% LiPF6 means that based on the total mass of the electrolyte, the mass fraction of LiODFB is 0.5% and the mass fraction of LiPF6 is 12%; the additive 0.5% 5-O-CN + 0.5% PCS means that based on the total mass of the electrolyte, the mass fraction of 5-O-CN is 0.5% and the mass fraction of PCS is 0.5%. 5-O-CN represents 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and its structural formula is as follows:

[0047]

[0048] 1,2,3,4,5-penta(2-cyanoethoxy)pentane can be prepared by mixing xylitol and sodium ethoxide and then adding acrylonitrile for reaction. As a preferred example, the preparation method of 1,2,3,4,5-penta(2-cyanoethoxy)pentane is as follows: Mix 152g of xylitol and 6.8g of sodium ethoxide, heat to 90°C and stir for 2 hours, then slowly add 477g of acrylonitrile and stir, react for 12h, cool to room temperature, add 6000g of ethanol and stir evenly, filter to obtain the filter residue, and recrystallize and purify the filter residue with ethyl acetate and n-hexane to obtain a finished product with a purity > 99%.

[0049] PCS represents 4-methyl vinyl sulfate.

[0050] As can be seen from Table 1, the use of a compound of 5-O-CN and PCS as an electrolyte additive can effectively improve the cycling performance and heat resistance of lithium-ion batteries.

[0051] When the compound of 5-O-CN and PCS is used as the additive, by comparing Examples 1 to 3, it is found that as the addition amount of 5-O-CN increases, the retention rates of the room-temperature and high-temperature cycling capacities of the battery both increase. However, as the addition amount of 5-O-CN further increases, the retention rates of the room-temperature and high-temperature cycling capacities of the battery decrease. Therefore, the addition amount of 5-O-CN is preferably not more than 1.5%. By comparing Examples 4 to 6, it is found that as the addition amount of PCS increases, the retention rates of the room-temperature and high-temperature cycling capacities of the battery both increase. As the addition amount of PCS further increases, although the retention rate of the high-temperature cycling capacity of the battery further increases, the retention rate of the room-temperature cycling capacity decreases. Therefore, in order to balance the room-temperature and high-temperature cycling performances, the addition amount of PCS is preferably 0.5-2%. By comparing Example 5 with Example 7 and Example 6 with Example 8, it is found that further optimizing the solvent system to increase the proportion of cyclic carbonates in the electrolyte can improve the room-temperature cycling performance of the battery.

[0052] The above has described the present invention in detail. The purpose is to enable those skilled in this field to understand the content of the present invention and implement it. However, the protection scope of the present invention cannot be limited thereby. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A non-aqueous electrolyte, comprising a lithium salt, an organic solvent and an additive, characterized in that: The additive includes 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 4-vinyl methyl sulfate.

2. The non-aqueous electrolyte according to claim 1, characterized in that: The additive accounts for 0.1% to 10% of the total mass of the non-aqueous electrolyte.

3. The non-aqueous electrolyte according to claim 2, characterized in that: The 1,2,3,4,5-penta(2-cyanoethoxy)pentane accounts for 0.1% to 1.5% of the total mass of the non-aqueous electrolyte; and / or, The 4-vinyl methyl sulfate accounts for 0.5% to 2% of the total mass of the non-aqueous electrolyte.

4. The non-aqueous electrolyte according to claim 1, characterized in that: The lithium salt includes a first lithium salt and a second lithium salt. The first lithium salt is selected from one or more of lithium hexafluorophosphate, lithium difluoro(oxalato)phosphate, lithium difluorophosphate, and lithium tetrafluoro(oxalato)phosphate. The second lithium salt is selected from one or more of lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate.

5. The non-aqueous electrolyte according to claim 4, characterized in that: The lithium salt accounts for 5% to 20% of the total mass of the non-aqueous electrolyte; and / or, The mass ratio of the first lithium salt to the second lithium salt is (20 to 30):

1.

6. The non-aqueous electrolyte according to claim 1, characterized in that: The organic solvent includes cyclic carbonates and linear carbonates. The cyclic carbonates account for 30% to 50% of the total mass of the organic solvent.

7. The non-aqueous electrolyte according to claim 6, characterized in that: The cyclic carbonates include one or more of ethylene carbonate and propylene carbonate; and / or, The linear carbonates include one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

8. A lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet and a separator, characterized in that: The lithium ion battery further includes the non-aqueous electrolyte according to any one of claims 1 to 7.

9. The lithium ion battery according to claim 8, wherein: The compaction density of the negative electrode plate is 1.45 to 1.65 g / cm 3 .

10. The lithium ion battery according to claim 8 or 9, characterized in that: The active material in the negative electrode sheet includes graphite; and / or, The active material in the positive electrode tab includes lithium iron phosphate, and the tap density of the positive electrode tab is 2 to 2.5 g / cm 3 .

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