An electrolyte for a lithium-ion battery and a lithium-ion battery using the same

Abstract

This application provides an electrolyte for lithium-ion batteries and a lithium-ion battery using the same. The electrolyte comprises a first additive and an organic solvent. The first additive has a mass fraction of 1.6–4.5% in the electrolyte, and the organic solvent has a mass fraction of 80–85%. The first additive includes fluorinated ether compounds, hexafluorobenzene, and vinylene carbonate, and the organic solvent includes ethylene glycol dimethyl ether. The mass ratio of the fluorinated ether compounds, hexafluorobenzene, and vinylene carbonate is 0.1–1:1–2:0.5–1.5. The electrolyte provided by this application can weaken the heat generated by oxygen release from high-nickel ternary cathode materials and suppress the heat generated by decomposition side reactions of the electrolyte, effectively suppressing the thermal runaway reaction of lithium-ion batteries, increasing their self-heating initiation temperature and thermal runaway initiation temperature, reducing the probability of thermal runaway in lithium-ion batteries containing high-nickel ternary cathode materials, and improving the safety performance of lithium-ion batteries.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to an electrolyte for lithium-ion batteries and a lithium-ion battery using the same. Background Technology

[0002] The continued prosperity of computer, communication and consumer electronics products has led to the rapid development of the lithium-ion battery industry. In particular, the rise of new energy vehicles in recent years has not only promoted the development of power lithium-ion batteries, but also put forward higher requirements for energy density and safety performance.

[0003] The application of high-nickel ternary cathode materials and silicon-based anode materials is an effective way to achieve high energy density in lithium-ion batteries. However, lithium-ion batteries containing high-nickel / high-silicon systems have poor safety performance and are prone to thermal runaway during practical applications, which has become one of the main bottlenecks restricting their large-scale industrial application. Lowering the self-heating initiation temperature and thermal runaway initiation temperature of lithium-ion batteries can effectively delay the triggering time of thermal runaway and effectively reduce the probability of thermal runaway or prevent its occurrence. Therefore, developing an electrolyte that can increase the self-heating initiation temperature and thermal runaway initiation temperature of lithium-ion batteries is extremely important for improving the safety performance of lithium-ion batteries containing high-nickel / high-silicon systems. Summary of the Invention

[0004] To address the poor safety performance of existing lithium-ion batteries containing high-nickel / high-silicon systems, and to improve the self-generated heat initiation temperature and thermal runaway initiation temperature of lithium-ion batteries, thereby reducing the risk of thermal runaway, this application provides an electrolyte for lithium-ion batteries and a lithium-ion battery using the same.

[0005] According to a first aspect of this application, an electrolyte for lithium-ion batteries is provided, comprising a first additive and an organic solvent, wherein the first additive has a mass fraction of 1.6–4.5% in the electrolyte, and the organic solvent has a mass fraction of 80–85% in the electrolyte; the first additive comprises a fluorinated ether compound, hexafluorobenzene, and vinylene carbonate, and the organic solvent comprises ethylene glycol dimethyl ether; the mass ratio of the fluorinated ether compound to hexafluorobenzene to vinylene carbonate is 0.1–1:1–2:0.5–1.5, for example, the first additive in… The mass fraction of the electrolyte can be 1.6%, 2.0%, 2.5%, 3.5%, 4.0%, or 4.5%, and the mass fraction of the organic solvent in the electrolyte can be 80%, 81%, 82%, 83%, 84%, or 85%. The mass ratio of fluorinated ethers, hexafluorobenzene, and vinylene carbonate can be 0.1:1:0.5, 0.5:1.5:1, 1:2:1.5, 0.1:2:1.5, or 1:1:0.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0006] The lithium-ion battery electrolyte provided in this application introduces fluorinated ether compounds, hexafluorobenzene, and vinylene carbonate as the first additive, and uses ethylene glycol dimethyl ether as the organic solvent. Fluorinated ether compounds (TTE) contain strongly polar CH groups, and hexafluorobenzene exhibits good thermal stability. The introduction of TTE, hexafluorobenzene, and vinylene carbonate (VC) into ethylene glycol dimethyl ether (DME) allows for the coordinated formation of intermolecular anchoring effects through hydrogen bonds among DME, resulting in high heat resistance of the electrolyte. This effectively reduces the electron cloud density on oxygen atoms, significantly improves the antioxidant capacity of the organic solvent, and thus weakens the oxygen release heat generation and inhibits electrolysis in the high-nickel ternary cathode material. The heat generated by the decomposition side reaction of the liquid effectively suppresses the thermal runaway reaction of lithium-ion batteries, increasing both the self-heating initiation temperature and the thermal runaway initiation temperature. This significantly reduces the probability of thermal runaway in lithium-ion batteries containing high-nickel ternary cathode materials, thus greatly improving the safety performance of lithium-ion batteries. Secondly, the introduction of vinylene carbonate (VC) can promote the formation of a solid electrolyte interphase (SEI) film on the negative electrode surface during the initial charge and discharge of lithium-ion batteries. This effectively suppresses the intercalation of organic solvent molecules and the gas expansion phenomenon of lithium-ion batteries, which can improve the safety performance of lithium-ion batteries to a certain extent and reduce the risk of thermal runaway in lithium-ion batteries containing silicon-based materials.

[0007] Preferably, the fluorinated ether compound includes at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,2-trifluoroethyl ether, and hexafluoroisopropyl methyl ether.

[0008] Preferably, the electrolyte further includes a second additive, the second additive having a mass fraction of 0.1% to 1% in the electrolyte. For example, the mass fraction of the second additive in the electrolyte may be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The second additive includes at least one of lithium difluorooxalate borate (LiDFOB) and lithium bis(oxalate borate) (LiBOB).

[0009] This solution introduces a second additive, LiDFOB and / or LiBOB, into the electrolyte and applies it to lithium-ion batteries, which helps to reduce the impedance of lithium-ion batteries and improve their high-temperature cycle life.

[0010] Preferably, the electrolyte further includes a lithium salt, wherein the mass fraction of the lithium salt in the electrolyte is 10-20%; the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), and lithium bistrifluoromethanesulfonylimide (LiTFSI).

[0011] Preferably, the lithium salt is composed of lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonyl imide (LiFSI) in a mass ratio of 9 to 15:1 to 5. For example, the mass ratio of LiPF6 to LiFSI can be 9:1, 12:3, 15:5, 9:5, 15:1, 12:1, 12:3, or 12:5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0012] This scheme uses LiPF6 and LiFSI in the above mass ratio as the lithium salt in the electrolyte. It has good thermal stability and is not sensitive to moisture. It can reduce the side reactions between the electrolyte and the positive and negative electrodes and increase the decomposition temperature of the electrolyte, which is beneficial to improving the safety of the electrolyte. At the same time, it improves the high-temperature cycle performance of lithium-ion batteries using this electrolyte, reduces the risk of thermal runaway of lithium-ion batteries in actual applications, and improves the safety performance of lithium-ion batteries.

[0013] Preferably, the organic solvents further include cyclic carbonate solvents and linear carbonate solvents; the cyclic carbonate solvents include at least one of ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC); the linear carbonate solvents include at least one of ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

[0014] Preferably, the organic solvents mentioned above include propylene carbonate, fluoroethylene carbonate, and dimethyl carbonate, and are calculated by mass ratio as follows: ethylene glycol dimethyl ether: propylene carbonate: fluoroethylene carbonate: dimethyl carbonate = 20-30: 10-22.5: 5-15: 25-36. For example, the mass ratio of ethylene glycol dimethyl ether, propylene carbonate, fluoroethylene carbonate, and dimethyl carbonate can be 20:10:5:25, 25:16:10:31, 30:22.5:15:36, or 20:17:10:25, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] Ethylene carbonate (EC) exacerbates the oxygen release reaction and heat generation in ternary high-nickel cathodes, leading to thermal runaway in lithium-ion batteries. In contrast, propylene carbonate (PC) has higher thermal stability and can increase the self-heating initiation temperature and thermal runaway initiation temperature, while weakening the oxygen release heat generation of the cathode.

[0016] This solution uses propylene carbonate (PC), fluoroethylene carbonate (FEC), and dimethyl carbonate (DMC) in the above mass ratio as the organic solvent in the electrolyte. The hexafluorobenzene in the electrolyte has a synergistic effect with PC, FEC, and DMC to reduce the impedance of lithium-ion batteries using this electrolyte, which is beneficial to improving the cycle stability of lithium-ion batteries.

[0017] According to a second aspect of this application, a lithium-ion battery is provided, the lithium-ion battery comprising the above-described electrolyte for lithium-ion batteries.

[0018] Preferably, the lithium-ion battery further includes a positive electrode sheet, which comprises a positive current collector and a positive active coating disposed on at least one surface of the positive current collector, the positive active coating containing a ternary positive electrode material LiNi. x Co y M 1-x-y O2, where 0.6≤x<1, 0<y<0.4, and M is selected from Mn and Al. For example, x can be 0.6, 0.7, 0.8, or 0.9, and y can be 0.1, 0.2, or 0.3, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, the lithium-ion battery further includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active coating disposed on at least one surface of the negative electrode current collector, the negative electrode active coating containing silicon-carbon material.

[0020] Preferably, the silicon content in the silicon-carbon material is 5 to 30 wt%. For example, the silicon content in the silicon-carbon material can be 5%, 10%, 15%, 20%, 25%, or 30%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Applying the electrolyte provided in this application to lithium-ion batteries containing high-nickel / high-silicon systems can effectively suppress the generation of thermal runaway reactions in lithium-ion batteries, thereby increasing both the self-generated heat initiation temperature and the thermal runaway initiation temperature of lithium-ion batteries. This significantly reduces the probability of thermal runaway in lithium-ion batteries containing high-nickel ternary cathode materials and high-silicon anode materials, thus greatly improving the safety performance of lithium-ion batteries. Detailed Implementation

[0022] The technical features of the technical solution provided in this application will be further clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] Examples 1-3 and Comparative Examples 1-4

[0024] Examples 1-3 and Comparative Examples 1-4 provide a lithium-ion battery prepared by the following steps:

[0025] 1. Preparation of positive electrode sheet

[0026] LiNi, a ternary cathode material 0.8 Co 0.1 Mn 0.1 O2, polyvinylidene fluoride (PVDF) binder, and acetylene black conductive agent were mixed in a mass ratio of 98.5:1.3:0.2 and then added to N-methylpyrrolidone (NMP) solvent. After thorough mixing, a positive electrode slurry with a solid content of 45% was obtained. This slurry was then coated onto both surfaces of a 12 μm thick aluminum foil current collector to form an active coating. After vacuum drying, a compacted density of 1.4 g / cm³ was obtained. 3 The positive electrode plate.

[0027] 2. Preparation of negative electrode sheet

[0028] Silicon-carbon material (silicon content 20wt%), sodium carboxymethyl cellulose binder (CMC) and conductive carbon black (SP) were mixed in a mass ratio of 96:3:1 and then added to deionized water as solvent. After mixing evenly, a negative electrode slurry with a solid content of 45% was prepared. The negative electrode slurry was coated on both surfaces of the negative electrode current collector copper foil (thickness 6μm) to form a negative electrode active coating. After vacuum drying, a negative electrode sheet was obtained.

[0029] 3. Preparation of the diaphragm

[0030] A polyethylene (PE) membrane containing a ceramic layer is used as the separator (the total thickness of the separator is 12 μm).

[0031] 4. Preparation of electrolyte

[0032] The specific components of the electrolyte are shown in Table 1. The electrolyte is prepared by the following steps: dissolving lithium salt in an organic solvent to prepare a lithium salt solution, adding the first additive and the second additive to the lithium salt solution, mixing evenly, and obtaining the electrolyte. Among them, TTE is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and THF is tetrahydrofuran.

[0033] Table 1. Specific components of the electrolytes in the lithium-ion batteries of Examples 1-3 and Comparative Examples 1-4.

[0034]

[0035] 5. Assembly and formation of lithium-ion batteries

[0036] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with the electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0037] Comparative Examples 5-10

[0038] Comparative Examples 5-10 provide a lithium-ion battery that differs from Example 1 in that the electrolyte composition is different, as shown in Table 2.

[0039] Table 2. Specific components of the electrolytes in the lithium-ion batteries of Examples 1 and Comparative Examples 5-10.

[0040]

[0041] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in Comparative Examples 5 to 10 were strictly consistent with those in Example 1.

[0042] Examples 4-10

[0043] Examples 4-10 provide a lithium-ion battery that differs from Example 1 in that the electrolyte composition is different, as shown in Table 3.

[0044] Table 3 shows the specific components of the electrolytes in the lithium-ion batteries of Examples 1 and 4-10.

[0045]

[0046]

[0047] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in Examples 4 to 10 are strictly consistent with those in Example 1.

[0048] Comparative Example 11 and Example 11

[0049] Example 11 and Comparative Example 11 provide a lithium-ion battery. Compared with Example 1, the difference in composition is that the electrolyte composition is different, as shown in Table 4.

[0050] Table 4. Specific components of the electrolytes in the lithium-ion batteries of Example 1, Comparative Example 11, and Example 11.

[0051]

[0052]

[0053] Apart from the differences mentioned above, the materials, formulation ratios, and preparation operations used in Comparative Example 11 and Example 11 are strictly consistent with those in Example 1.

[0054] Test case

[0055] 1. Participants

[0056] This test example uses the lithium-ion batteries prepared in Examples 1-11 and Comparative Examples 1-11 as test objects to conduct relevant performance tests.

[0057] 2. Test Content

[0058] (1) 150℃ & 0.5h - clampless thermal abuse thermal runaway time and temperature monitoring test

[0059] After fully charging the lithium-ion battery (100% SOC), it was placed in a temperature chamber and heated from room temperature to 150±2℃ at a rate of 5℃ / min. This temperature was maintained for 30 minutes, after which heating was stopped, and the battery was observed for 1 hour. Two parallel experiments were performed for each example or comparative example to observe whether the lithium-ion battery caught fire. Simultaneously, the temperature changes of the lithium-ion battery (thermal runaway T2 delay time, thermal runaway trigger temperature T2, and thermal runaway peak temperature T3) were recorded. For Comparative Example 1, the thermal runaway T2 delay time refers to the time during the heating process... The heating time at which thermal runaway initiation temperature is reached, while the thermal runaway T2 delay time of Examples 1-11 and Comparative Examples 2-11 is relative to Comparative Example 1, that is, it is calculated by subtracting the heating time of the lithium-ion battery of Comparative Example 1 from the heating time of the lithium-ion battery of Comparative Example 1 at the thermal runaway initiation temperature during the heating process; the thermal runaway trigger temperature T2 is the temperature rise rate greater than 1℃ / min; the thermal runaway peak temperature T3 is the highest thermal runaway temperature.

[0060] (2) Accelerated Calorimeter (ARC) Thermal Runaway Test

[0061] The working principle of an accelerating rate calorimeter (ARC) is to provide a (near) adiabatic environment and use a "heat-wait-seek" mode to heat the lithium-ion battery in steps, simulating the thermal runaway process of a lithium-ion battery when there is no heat exchange between the lithium-ion battery and the environment.

[0062] After fully charging a lithium-ion battery (100% SOC), placing it in the ARC calorimetric chamber (nitrogen atmosphere) allows for monitoring of the battery's temperature changes (self-heating initiation temperature T1, thermal runaway initiation temperature T2, and maximum temperature T) in an adiabatic environment. maxRecord the following three characteristic temperatures for thermal runaway in lithium batteries: Self-generated heat initiation temperature T1 – temperature rise rate greater than 0.01℃ / min; Thermal runaway trigger / initiation temperature T2 – temperature rise rate greater than 1℃ / min; Maximum thermal runaway temperature T... max .

[0063] 3. Experimental Results

[0064] Table 5. Test results of thermal runaway time and temperature monitoring of lithium-ion batteries under unsecured thermal abuse at 150℃ for 0.5h.

[0065]

[0066]

[0067] Table 6 Results of ARC thermal runaway test for lithium-ion batteries

[0068]

[0069]

[0070] Table 5 shows the test results of thermal runaway time and temperature monitoring of lithium-ion batteries provided in Examples 1-11 and Comparative Examples 1-11 at 150℃ for 0.5h without clamps. Table 6 shows the test results of thermal runaway (ARC) of lithium-ion batteries provided in Examples 1-11 and Comparative Examples 1-11. In Table 5, the "2PCS" after "2PCS / 2PCS fire" refers to the total number of lithium-ion batteries being 2, and the "2PCS" before "2PCS" refers to the number of lithium-ion batteries that caught fire being 2.

[0071] The temperature rise curves during the 150°C hot box test show that the thermal runaway time of the lithium-ion batteries provided in Examples 1-3 is approximately 13-22 minutes longer than that of the lithium-ion battery provided in Comparative Example 1, and the T2 temperature is increased by approximately 10-45°C, while the T3 temperature is significantly reduced by approximately 300°C. The battery ARC thermal runaway time (T1 / T2 / T) is also significantly reduced. max Temperature tests show that the thermal runaway time of the lithium-ion batteries provided in Examples 1-3 is 19-20°C longer than that of the lithium-ion battery provided in Comparative Example 1, and the thermal runaway triggering temperature T2 is 20-24°C longer. These results indicate that the thermal runaway of the lithium-ion batteries provided in Examples 1-3 is delayed and the probability of thermal runaway is reduced, thus improving the safety of the lithium-ion batteries.

[0072] Compared with Example 1, the electrolyte in the lithium-ion battery provided by Comparative Example 2 does not contain VC, the electrolyte in the lithium-ion battery provided by Comparative Example 3 does not contain hexafluorobenzene, the electrolyte in the lithium-ion battery provided by Comparative Example 4 does not contain DME, the electrolytes in the lithium-ion batteries provided by Comparative Examples 5 and 6 contain a mass fraction of the first additive that does not meet the requirement of 1.5-3.5%, and the electrolytes in the lithium-ion batteries provided by Comparative Examples 7 and 8 contain a mass fraction of the first additive that meets the requirement of 1.5-3.5%, but the mass ratio of hexafluorobenzene to vinylene carbonate does not meet the requirement of 1-2:0.5-1.5. The test results show that the lithium batteries provided by Comparative Examples 2-8 have a shorter thermal runaway delay time (T2) and a shorter thermal runaway trigger temperature (T2) than those in Example 1 during the 150°C hot box test, and a higher thermal runaway peak temperature (T3) than those in Example 1. However, during the ARC thermal runaway test, the self-generated heat initiation temperature (T1) and the thermal runaway initiation temperature (T2) are both lower than those in Example 1, and the highest temperature (T) is lower than that in Example 1. max All were higher than in Example 1.

[0073] Compared with Example 1, the electrolytes in the lithium-ion batteries provided in Examples 4 and 5 contained less than 0.1-1% of the second additive, and the electrolytes in the lithium-ion batteries provided in Examples 7 and 8 contained less than 10-20% of the lithium salt. Test results showed that the lithium batteries provided in Comparative Examples 2-8 had shorter thermal runaway delay times (T2) and trigger temperatures (T2) than those in Example 1 during the 150°C hot box test, while their peak thermal runaway temperatures (T3) were higher than those in Example 1. However, during the ARC thermal runaway test, their self-generated heat initiation temperatures (T1 and T2) were lower than those in Example 1, and their highest temperature (T) was lower. max All were higher than in Example 1.

[0074] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application, but such modifications or substitutions are all within the scope of protection of this application.

Claims

1. An electrolyte for lithium-ion batteries, characterized in that: The electrolyte comprises a first additive, a lithium salt, and an organic solvent, wherein the first additive has a mass fraction of 1.6-4.5% in the electrolyte, and the organic solvent has a mass fraction of 80-85% in the electrolyte. The first additive includes fluorinated ether compounds, hexafluorobenzene, and vinylene carbonate, and the organic solvent includes ethylene glycol dimethyl ether; The mass ratio of the fluorinated ether compound to the hexafluorobenzene to the vinylene carbonate is 0.1~1:1~2:0.5~1.

5. The organic solvent includes propylene carbonate, fluoroethylene carbonate, and dimethyl carbonate, and the mass ratio of ethylene glycol dimethyl ether: propylene carbonate: fluoroethylene carbonate: dimethyl carbonate is 20~30: 10~22.5: 5~15: 25~36. The lithium salt is composed of lithium hexafluorophosphate and lithium difluorosulfonyl imide in a mass ratio of 9~15:1~5.

2. The electrolyte for lithium-ion batteries as described in claim 1, characterized in that: The fluoroether compounds include at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,2-trifluoroethyl ether, and hexafluoroisopropyl methyl ether.

3. The electrolyte for lithium-ion batteries as described in claim 1, characterized in that: The electrolyte further includes a second additive, wherein the mass fraction of the second additive in the electrolyte is 0.1% to 1%. The second additive includes at least one of lithium difluorooxalate borate and lithium dioxalate borate.

4. The electrolyte for lithium-ion batteries as described in claim 1, characterized in that: The lithium salt has a mass fraction of 10-20% in the electrolyte.

5. The electrolyte for lithium-ion batteries as described in claim 1, characterized in that: The organic solvents also include cyclic carbonate solvents and linear carbonate solvents; The cyclic carbonate solvents include at least one of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. The linear carbonate solvents include at least one of ethyl methyl carbonate and dimethyl carbonate.

6. A lithium-ion battery, characterized in that: The lithium-ion battery includes the electrolyte for lithium-ion batteries as described in any one of claims 1 to 5.

7. The lithium-ion battery as described in claim 6, characterized in that: The lithium-ion battery further includes a positive electrode sheet, which comprises a positive current collector and a positive active coating disposed on at least one surface of the positive current collector, the positive active coating containing a ternary positive electrode material LiNi. x Co y M 1-x-y O2, where 0.6≤x<1, 0<y<0.4, and M is selected from Mn and Al.

8. The lithium-ion battery as described in claim 6, characterized in that: The lithium-ion battery further includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active coating disposed on at least one surface of the negative electrode current collector, the negative electrode active coating containing silicon-carbon material.

9. The lithium-ion battery as described in claim 8, characterized in that: The silicon content in the silicon-carbon material is 5-30 wt%.

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