Lithium ion battery electrolyte and lithium ion battery

Abstract

The present application relates to a kind of lithium ion battery electrolyte and lithium ion battery, to solve the problem that lithium ion battery electrolyte in the prior art cannot simultaneously consider the normal temperature cycle performance, high temperature storage safety and low temperature discharge efficiency of lithium ion battery, the present application provides a kind of lithium ion battery electrolyte, it includes solvent, lithium salt and additive, wherein additive includes nitrobenzonitrile derivative, nitrobenzonitrile derivative is one or more of the compound shown in general formula (1), general formula (1) is: R1, R2 It is independently H, F, alkyl, fluoroalkyl, oxygen alkyl, sulfur alkyl, nitro or cyano, and nitrobenzonitrile derivative does not include p-nitrobenzonitrile.The lithium ion battery electrolyte of the present application has obvious improvement to the normal temperature cycle performance, high temperature storage performance and low temperature discharge performance of lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a lithium-ion battery electrolyte and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries have advantages such as high energy density, high operating voltage, no memory effect, rapid charging and discharging, and low environmental pollution, and are therefore widely used. However, with increasing demands on the energy density, safety performance, and lifespan of commercial lithium-ion batteries, the development of lithium-ion batteries with high energy density, good cycle performance, and high safety is an urgent need for the industry.

[0003] During the initial charging of a lithium-ion battery, the electrolyte reacts with the carbon anode to form a passivation film (SEI film). Lithium ions must pass through the SEI film during charging and discharging, thus significantly impacting the battery's key performance characteristics, such as cycle life, high-temperature performance, and power output. The SEI film prevents further electrolyte decomposition and reduces side reactions at the anode interface. However, as charging and discharging progress, the SEI film may dissolve, rupture, decompose, recombine, or thicken, leading to increased internal resistance or gas production, negatively affecting cycle life, capacity utilization, and safety. These negative effects are exacerbated during high-temperature storage or cycling. Furthermore, as lithium-ion battery voltage increases, a good passivation film (CEI film) also needs to form on the positive electrode side during cycling. Different additives in the electrolyte, or even different amounts of the same additive, result in varying SEI film quality and impedance. Therefore, selecting appropriate additives and electrolyte formulations to improve SEI / CEI film quality is crucial for achieving high-performance lithium-ion batteries.

[0004] Increasing the operating voltage provides higher energy density for lithium-ion batteries. However, the resulting capacity decay hinders their commercial application. On one hand, many researchers believe that currently used commercial carbonate-based electrolytes cannot withstand higher voltages. Although commercial carbonate-based electrolytes exhibit a high electrochemical window in redox tests of inert electrodes, the catalytic effect of transition metals on the electrolyte must be considered in practical applications. This prevents current commercial carbonate-based electrolytes from maintaining high-voltage battery cycling for extended periods. On the other hand, when the cutoff voltage of lithium cobalt oxide batteries reaches 4.5V, the CEI interface formed by traditional carbonate-based electrolytes is very fragile. When this fragile interface breaks, Co ions will detach from the material and enter the electrolyte, migrate to the negative electrode side, undergo a reduction reaction, destroy the SEI of the negative electrode, and cause battery failure. Furthermore, catalytically active transition metal ions will further catalyze electrolyte decomposition, creating an irreversible vicious cycle. Meanwhile, under high voltage, the electrochemical stability of the electrolyte deteriorates, making it prone to decomposition and the generation of HF, which corrodes the SEI film and consequently affects the Li. + De-embedding.

[0005] Silicon anodes suffer from severe volume expansion problems, which require a stable SEI film to suppress.

[0006] When high-voltage lithium cobalt oxide is matched with a silicon anode battery, as the voltage increases, the carbonate and lithium hexafluorophosphate in the electrolyte further react to produce HF. High voltage catalyzes this hydrolysis reaction, primarily due to PF6. – The structural oxidation stability decreases upon combining with water, and the decomposition energy barrier decreases, ultimately leading to an intensified hydrolysis reaction. HF corrodes the SEI film on the surface of the silicon anode, making the volume expansion problem of the silicon anode more pronounced, which in turn leads to a significant degradation in the performance of full cells matched with high-voltage lithium cobalt oxide and silicon anode batteries. Simultaneously, during charging, as the voltage increases, more lithium ions are inserted into the silicon anode; however, due to the uneven insertion of Li, extreme volume expansion and contraction occur in localized areas of the Si electrode. This generates accumulated stress in these areas, causing the Si electrode to disintegrate and resulting in poor cycle performance.

[0007] Compared to high-voltage lithium cobalt oxide / graphite batteries, the same formulation exhibits more significant performance degradation in high-voltage lithium cobalt oxide / silicon-based anode batteries. The crosstalk effect of transition metal Co may have a significantly different impact on the SEI chemistry and performance of Si-based batteries, as well as their aging behavior, compared to traditional graphite-based batteries. The surface chemistry of the anode material affects the electrolyte, causing the SEI chemistry of the Si / graphite composite electrode to vary with Si content, or Si may readily form various more stable alloys or Zintl phases with multiple metal ions. The significantly lower electronic conductivity of Si compared to graphite may also be another reason, as this lower electronic conductivity kinetically hinders the reduction reactions of transition metal ions. For example, adiponitrile (ADN) and 1,3,6-hexanetrionitrile (HTCN) can significantly improve the cycle performance of high-voltage lithium cobalt oxide / graphite batteries, but not in high-voltage lithium cobalt oxide / silicon-based anode batteries. This may be because cyano groups can complex with metal ions (Co), preventing Co from degrading the graphite anode, but Co has no effect on the silicon anode; instead, it leads to an increase in the impedance of the silicon anode, thus degrading the performance of the silicon anode battery. Therefore, new additives are needed to compensate for the degradation of battery performance. Summary of the Invention

[0008] The purpose of this invention is to provide a lithium-ion battery electrolyte that can balance the high-voltage room-temperature cycling performance, high-temperature storage safety, and low-temperature discharge efficiency of lithium-ion batteries, as well as a lithium-ion battery using the electrolyte.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A lithium-ion battery electrolyte includes a solvent, a lithium salt, and an additive, wherein the additive includes a nitrobenzene derivative, and the nitrobenzene derivative is one or more compounds represented by general formula (1), wherein general formula (1) is:

[0011]

[0012] R1 and R2 are independently H, F, alkyl, fluoroalkyl, oxyalkyl, thioalkyl, nitro or cyano, and the nitrobenzonitrile derivatives do not include p-nitrobenzonitrile.

[0013] Preferably, R1 and R2 are independently H, F, an alkyl group having 1 to 3 carbon atoms, a fluoroalkyl group having 1 to 3 carbon atoms, an oxoalkyl group having 1 to 3 carbon atoms, a thioalkyl group having 1 to 3 carbon atoms, a nitro group, or a cyano group, and the nitrobenzonitrile derivative does not include p-nitrobenzonitrile.

[0014] The alkyl group referred to in this invention can be either a straight-chain alkyl group or a branched-chain alkyl group.

[0015] Preferably, the nitrobenzonitrile derivative is one or more of the following compounds A to N:

[0016]

[0017] Preferably, the mass of the nitrobenzonitrile derivative accounts for 1% to 8% of the total mass of the lithium-ion battery electrolyte.

[0018] More preferably, the mass of the nitrobenzonitrile derivative accounts for 1% to 5% of the total mass of the lithium-ion battery electrolyte.

[0019] More preferably, the mass of the nitrobenzonitrile derivative accounts for 2% to 4% of the total mass of the lithium-ion battery electrolyte.

[0020] Preferably, the solvent is one or more of carbonates, carboxylic esters, and ethers.

[0021] More preferably, the carbonate is one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate.

[0022] More preferably, the carboxylic acid ester is one or more selected from propyl propionate, ethyl acetate, ethyl butyrate, and methyl propionate.

[0023] More preferably, the ether is ethylene glycol dimethyl ether and / or 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0024] More preferably, the solvent is a mixture of carbonates and carboxylic acids.

[0025] More preferably, the solvent comprises at least dimethyl carbonate and carboxylic acid ester, and the sum of the masses of the dimethyl carbonate and the carboxylic acid ester accounts for 10% to 40% of the total mass of the solvent, for example, 10%, 15%, 20%, 25%, 30%, 35%, or 40%.

[0026] More preferably, the sum of the masses of the dimethyl carbonate and the carboxylic acid ester accounts for 25% to 35% of the total mass of the solvent.

[0027] Preferably, the lithium salt is one or more of LiClO4, LiPF6, LiTFSI, and LiFSI.

[0028] Preferably, the molar concentration of the lithium salt in the lithium-ion battery electrolyte is 0.001 to 2 mol / L.

[0029] More preferably, the molar concentration of the lithium salt in the lithium battery electrolyte is 0.1 to 2 mol / L.

[0030] More preferably, the molar concentration of the lithium salt in the lithium battery electrolyte is 1 to 1.5 mol / L.

[0031] Preferably, the additive further includes other additives, which are one or more of fluoroethylene carbonate, lithium tetrafluoroborate, and lithium difluorophosphate.

[0032] In this invention, the other additives preferably account for 3% to 15% of the total mass of the lithium-ion battery electrolyte, and more preferably 5% to 10%.

[0033] The present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the lithium-ion battery electrolyte described above.

[0034] In this invention, the positive electrode of the lithium-ion battery is lithium cobalt oxide, and the negative electrode is a silicon-containing material, which is not limited to nano-silicon, silicon suboxide, or silicon-carbon.

[0035] In this invention, the upper limit voltage of the lithium cobalt oxide cathode material for lithium-ion batteries is ≥4.55V.

[0036] The lithium battery electrolyte of this invention improves the quality of the SEI / CEI film by selecting nitrobenzonitrile derivatives with general formula (1) and optimizing the electrolyte formulation, thereby significantly improving the performance of the lithium-ion battery. The lithium-ion battery of this invention can achieve a capacity retention rate of up to 93% after 300 cycles at 1.0C at 25°C, and a swelling rate of up to 19% after being placed at 60°C for 30 days, achieving good technical results.

[0037] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0038] The lithium battery electrolyte of the present invention can improve the performance of lithium batteries. The lithium-ion batteries prepared using the electrolyte of the present invention have the advantages of good high-voltage cycling performance at room temperature, low expansion rate at high temperature and high discharge efficiency at low temperature, and have great application prospects. Detailed Implementation

[0039] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0040] Unless otherwise specified, the experimental methods used in the following examples and comparative examples are conventional methods; the experimental materials used, unless otherwise specified, were purchased from conventional biochemical reagent manufacturers.

[0041] Examples 1 to 27 and Comparative Examples 1 to 9 provide different electrolytes, and the specific formulations are shown in Table 1.

[0042] Table 1

[0043]

[0044]

[0045] EC: Ethylene carbonate; PC: Propylene carbonate; DMC: Dimethyl carbonate; EMC: Ethyl methyl carbonate; EA: Ethyl acetate; LiPF6: Lithium hexafluorophosphate; FEC: Fluorinated ethylene carbonate; LiODFB: Lithium difluorooxalate borate; LiPO2F2: Lithium difluorophosphate; LiNO3: Lithium nitrate; SBN: Sebaconitrile; A: B: C: D: E: F: G: H: I: J: K: L: M: N:

[0046] The structural formula of p-nitrobenzonitrile used in Comparative Examples 2-5 and Comparative Example 7 is as follows:

[0047]

[0048] Performance testing:

[0049] The electrolytes of Examples 1 to 27 and Comparative Examples 1 to 9 were assembled with positive and negative electrodes using conventional processes to form lithium-ion batteries. The negative electrode was a C material doped with 20% Si, and the positive electrode was a 4.55V LCO material.

[0050] The lithium-ion battery prepared above was tested by charging it to 4.55V at 1.0C constant current at 25℃ and then discharging it to 2.75V at 1.0C constant current. The battery capacity retention rate after 300 charge-discharge cycles was calculated as follows: 300-cycle capacity retention rate (%) = Discharge capacity of lithium-ion battery after 300 cycles / Average discharge capacity of lithium battery in the first 5 weeks of cycle × 100.

[0051] The swelling rate of the lithium-ion batteries prepared in each embodiment and comparative example was tested after being placed at 60°C for 30 days. The swelling rate (%) = (thickness of lithium battery after 30 days of placement - thickness of lithium battery before placement) / thickness of lithium battery before placement × 100.

[0052] The lithium-ion battery prepared above was charged to 4.55V at a constant current of 1.0C at room temperature (25℃). The discharge efficiency at 0.2C to 2.75V at -20℃ was tested. The discharge efficiency at -20℃ at 0.2C (%) = discharge capacity of lithium-ion battery at -20℃ at 0.2C / charge capacity of lithium-ion battery at room temperature at 0.2C × 100.

[0053] The performance test results are shown in Table 2.

[0054] Table 2

[0055]

[0056]

[0057] As shown in Tables 1 and 2, in high-voltage 4.55V lithium cobalt oxide and silicon-carbon anode matched full cells, compared with the basic formulation (Comparative Example 6), the lithium batteries with different nitrobenzonitrile derivatives showed improved high-voltage room-temperature cycling performance. Simultaneously, gas production was suppressed after the lithium batteries were stored at 60°C for 30 days. The nitrobenzonitrile derivatives used in the examples, whether used alone or in combination with other additives, showed better improvement effects on the room-temperature cycling performance, high-temperature gas production performance, and low-temperature discharge performance of the lithium batteries than SS, SBN, or LiNO3. The improvement effect was even more pronounced when nitrobenzonitrile derivatives were used in combination with FEC, LiODFB, and LiPO2F2.

[0058] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes made in accordance with the spirit and essence of the present invention are excluded.

Claims

1. A lithium-ion battery electrolyte comprising a solvent, a lithium salt and an additive, characterized in that: The additive comprises one or more of the nitrobenzonitrile derivatives in compounds A-N: , , , , , , , , , , , , , , the mass of the nitrophenyl cyanide derivative accounts for 1% to 8% of the total mass of the lithium ion battery electrolyte.

2. The electrolyte for lithium ion batteries according to claim 1, characterized in that: The solvent is one or more of carbonates, carboxylic acid esters, ethers.

3. The electrolyte for lithium-ion batteries according to claim 2, characterized in that: The carbonates are one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate; the carboxylic acid esters are one or more of propyl propionate, ethyl acetate, ethyl butyrate, methyl propionate; the ethers are dimethyl ether of ethylene glycol and / or 1,1,2,2-tetrafluoroethyl-2,2,3,3 tetrafluoropropyl ether.

4. The electrolyte for lithium ion batteries according to claim 2, characterized in that: The solvent at least comprises dimethyl carbonate and carboxylic acid ester, and the sum of the mass of the dimethyl carbonate and the carboxylic acid ester accounts for 10% to 40% of the total mass of the solvent.

5. The electrolyte for lithium-ion batteries according to claim 1, characterized in that: The lithium salt is one or more of LiClO4, LiPF6, LiTFSI, LiFSI; the molar concentration of the lithium salt in the lithium ion battery electrolyte is 0.001 to 2 mol / L.

6. The electrolyte for lithium-ion batteries according to claim 1, characterized in that: The additive further comprises other additives, which are one or more of fluorinated ethylene carbonate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, lithium difluorophosphate.

7. A lithium-ion battery comprising a positive electrode, a negative electrode and an electrolyte, characterized in that: The electrolyte is the lithium ion battery electrolyte according to any one of claims 1 to 6.

Images