Electrolyte composite additive, electrolyte and lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte composite additive, an electrolyte and a lithium ion battery. The electrolyte composite additive comprises a functional additive A and a functional additive B; the structural formula of the functional additive A is # imgabs0 #; r1 is selected from any one of halogen and substituted or unsubstituted phenyl. The structural formula of the functional additive B is # imgabs 1 #; r2 and R3 are respectively and independently selected from any one of substituted or unsubstituted C2-C6 alkyl groups, substituted or unsubstituted silicon groups, substituted or unsubstituted phenyl groups and C6-C7 cycloalkyl groups. The problem that the high-temperature storage performance of an existing battery becomes poor is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to an electrolyte composite additive, an electrolyte and a lithium ion battery. Background Art

[0002] With the rapid development of electric vehicles and high-end portable electronic devices, high-energy-density lithium-ion batteries have become mainstream in the market. High-nickel ternary cathode materials, with their superior specific capacity and power characteristics, have become a key technology for meeting the demands for long battery life and fast charging. However, ternary batteries, especially high-nickel systems, face a significant and common challenge in practical applications: storage stability in high-temperature environments. Batteries are inevitably exposed to high temperatures during their lifecycle, such as during vehicle parking in hot climates (where cabin temperatures can reach over 60°C), heat accumulation during fast charging, energy storage deployment in hot regions, or the use or storage of electronic devices in high-temperature environments. Under these conditions, ternary batteries, especially high-nickel materials, experience significantly accelerated degradation: the highly active nickel element exacerbates interfacial side reactions with the electrolyte, leading to irreversible loss of active lithium, dissolution of transition metal ions, the formation of thick and highly resistive interfacial films, and severe gas evolution. The direct consequences are a significant drop in battery capacity after storage, a sharp increase in internal resistance, a significant reduction in cycle life, swelling, and even increased safety risks.

[0003] Although existing technologies (such as cathode doping and coating, and electrolyte additive optimization) attempt to alleviate this problem, their effectiveness is often limited or suffers from cost, process complexity, and performance trade-offs under harsh high-temperature (e.g., ≥60°C) and long-term storage (e.g., weeks) conditions. High-temperature storage performance has become one of the most critical bottlenecks restricting the large-scale commercial application of ternary batteries, especially high-nickel ternary batteries, as well as user confidence and long-term product reliability. Improving their chemical and structural stability at high temperatures and inhibiting capacity decay and impedance growth are core requirements for breaking through current technical barriers and realizing broader application prospects for ternary batteries. Summary of the Invention

[0004] The purpose of the present invention is to provide an electrolyte composite additive, an electrolyte and a lithium ion battery, which solve the problem of poor high-temperature storage performance of existing batteries.

[0005] The present invention is achieved through the following technical solutions: The present invention discloses an electrolyte composite additive, comprising a functional additive A and a functional additive B; The structural formula of functional additive A is: ; Wherein, R1 is selected from any one of halogen, substituted or unsubstituted phenyl; The structural formula of functional additive B is: ; Wherein, R2 and R3 are each independently selected from any one of a substituted or unsubstituted C2-C6 alkyl group, a substituted or unsubstituted silicon group, a substituted or unsubstituted phenyl group, and a C6-C7 cycloalkyl group.

[0006] Furthermore, the electrolyte functional additive A is selected from one of the following structural formulas: 、 、 、 、 .

[0007] Furthermore, the functional additive B is selected from one of the following structural formulas: 、 、 、 、 、 、 、 、 、 、 .

[0008] The present invention also discloses an electrolyte, which includes a lithium salt and an electrolyte additive, wherein the electrolyte additive includes the electrolyte composite additive; Taking the total mass of the electrolyte as 100%, functional additive A accounts for (0.3~0.5)%; functional additive B accounts for (0.2~0.4)%; and lithium salt accounts for (12.5~15)%.

[0009] Furthermore, the electrolyte additives also include sulfur-containing additives, nitrile additives and lithium salt additives.

[0010] Furthermore, based on the total mass of the electrolyte being 100%, the sulfur-containing additives account for (0.5-1)%, the nitrile additives account for (0.3-0.5)%, and the lithium salt additives account for (0.5-1)%.

[0011] Furthermore, the sulfur-containing additive includes at least one of 1,3-propylene sultone and 1,3-propane sultone; The nitrile additive includes at least one of succinonitrile and adiponitrile; The lithium salt additive includes at least one of lithium difluorophosphate and lithium bis(fluorosulfonyl)imide.

[0012] Furthermore, the electrolyte also includes an organic solvent, and the organic solvent includes fluoroethylene carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate.

[0013] Furthermore, the lithium salt is lithium hexafluorophosphate.

[0014] The invention also discloses a lithium ion battery comprising a positive electrode, a negative electrode and the electrolyte.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention provides an electrolyte composite additive, which includes a functional additive A and a functional additive B. The functional additive A directly releases Li + Compensating for the loss and forming a solid electrolyte interface (SEI) film rich in LiF / Li2SO4 at the negative electrode, functional additive A can reduce the initial direct current resistance (DCR) and inhibit the growth of DCR during fast charge cycles, greatly improving the cycle performance. However, functional additive A decomposes at high temperatures to generate hydrofluoric acid, which corrodes the positive electrode interface, causing transition metal ions to dissolve, deteriorating high temperature performance, and triggering crosstalk reactions. After adding functional additive B, functional additive B contains -N=C=N- functional groups, which capture H + / H2O, reducing acidity and inhibiting free acid corrosion on the positive electrode, blocking lithium loss caused by acid corrosion, and improving high-temperature performance. Functional Additive A and Functional Additive B work synergistically to form a closed-loop "lithium replenishment-acid removal-interface stabilization" system. Their combined use effectively inhibits lithium dendrite growth and transition metal ion dissolution, stabilizes the positive electrode structure, and significantly enhances the battery's fast-charging performance and high-temperature stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The free acid content in the battery after 15 days of storage; Figure 2 To test the electrical performance of soft-pack batteries, the impedance diagram of the battery after 250 cycles of fast charging is shown. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clear, the following is further described in detail with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. That is, the embodiments described are only part of the embodiments of the present invention, not all embodiments.

[0018] The detailed description of the embodiment of the present invention provided below is not intended to limit the scope of the claimed invention, but is merely an example of a selected embodiment of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0019] The main purpose of the present invention is to provide an electrolyte additive, an electrolyte and a lithium-ion battery, which can solve the problem in the related art that the acidity inside the battery increases during high-temperature storage, resulting in poor high-temperature storage performance, while improving fast charging.

[0020] In order to achieve the above-mentioned object, the present invention provides an electrolyte composite additive, comprising a functional additive A and a functional additive B.

[0021] The general formula of functional additive A is Formula I: .

[0022] Wherein, R1 is selected from any one of halogen, substituted or unsubstituted phenyl.

[0023] Functional additive A is selected from one of the following structural formulas: 、 、 、 、 .

[0024] The general formula of functional additive B is Formula II: .

[0025] Wherein, R2 and R3 are each independently selected from any one of a substituted or unsubstituted C2-C6 alkyl group, a substituted or unsubstituted silicon group, a substituted or unsubstituted phenyl group, and a C6-C7 cycloalkyl group.

[0026] The functional additive B is selected from one of the following structural formulas: 、 、 、 、 、 、 、 、 、 、 .

[0027] Functional additive A hydrolyzes to generate lithium fluoride and lithium sulfate, which improves the quality of negative electrode film formation, reduces the initial direct current resistance (DCR) and the DCR growth rate during fast charging. Functional additive B contains a -N=C=N- group. The N atom in the group contains a lone pair of electrons and is weakly alkaline, which can neutralize the water and hydrofluoric acid generated during high-temperature storage. Functional additives A and B are used together to form a closed loop of "lithium replenishment-acid removal-interface stabilization". Functional additive A directly releases Li + , compensate for the loss, and generate a solid electrolyte interface (SEI) film rich in lithium fluoride and lithium sulfate at the negative electrode. Functional additive B reduces the consumption of lithium ions caused by acid, directly removes water and hydrofluoric acid, and the addition of the two together inhibits the formation of lithium dendrites, inhibits the dissolution of transition metal ions, stabilizes the positive electrode structure, and improves fast charging and high-temperature storage performance.

[0028] The present invention provides an electrolyte, comprising a lithium salt and an electrolyte additive, wherein the electrolyte additive comprises a functional additive A and a functional additive B. Based on 100% of the total mass of the electrolyte, the functional additive A accounts for (0.3-0.5)%, and the functional additive B accounts for (0.2-0.4)%.

[0029] Preferably, the electrolyte further comprises an organic solvent, and the organic solvent comprises cyclic carbonates and chain carbonates, wherein the cyclic carbonates comprise fluoroethylene carbonate and ethylene carbonate, and the chain carbonates comprise diethyl carbonate and ethyl methyl carbonate.

[0030] Based on the total mass of the organic solvent being 100%, the total mass of fluoroethylene carbonate and ethylene carbonate is 20%-24%, the mass of diethyl carbonate is 20%-25%, and the mass of ethyl methyl carbonate is 55%-60%.

[0031] Preferably, the lithium salt is lithium hexafluorophosphate (LiPF6), and the mass percentage of the lithium salt in the electrolyte is 12.5% ​​to 15%.

[0032] Preferably, the electrolyte additives further include sulfur-containing additives, nitrile additives, and lithium salt additives. Based on the total mass of the electrolyte as 100%, the sulfur-containing additives account for (0.5-1)%, the nitrile additives account for (0.3-0.5)%, and the lithium salt additives account for (0.5-1)%.

[0033] Among them, the sulfur-containing additive includes at least one of 1,3-propylene sultone (PST) and 1,3-propane sultone (PS); the nitrile additive includes at least one of succinonitrile (SN) and adiponitrile (ADN); and the lithium salt additive is at least one of lithium difluorophosphate (LiPO2F2) and lithium bis(fluorosulfonyl)imide.

[0034] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0035] Example 1 Calculated according to the mass percentage of the components, the electrolyte formula used in this embodiment is as follows: functional additive A (such as lithium fluorosulfonate of formula I-1): 0.3%, functional additive B (such as N,N'-diisopropylcarbodiimide of formula II-1): 0.2%, LiPO2F2: 0.8%, PS: 0.5%, SN: 0.3%, LiPF6: 15%, and the balance is organic solvent.

[0036] The organic solvent component in the above electrolyte formulation consists of fluoroethylene carbonate, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate. Calculated based on the total mass of the organic solvent as 100%, the mass proportion of fluoroethylene carbonate is 3%, the mass proportion of ethylene carbonate is 18%, the mass proportion of diethyl carbonate is 22%, and the mass proportion of ethyl methyl carbonate is 57%. Different embodiments were set up using the electrolyte functional additives in the above formulation as variables.

[0037]

[0038] Example 2 This embodiment provides an electrolyte additive and an electrolyte. The only difference between this embodiment and embodiment 1 is that the amount of the functional additive B added to the electrolyte is 0.3%. Other aspects are the same as those of embodiment 1.

[0039] Example 3 This embodiment provides an electrolyte additive and an electrolyte. The only difference between this embodiment and embodiment 1 is that the amount of the functional additive B added to the electrolyte is 0.4%. Other aspects are the same as those of embodiment 1.

[0040] Example 4 This embodiment provides an electrolyte additive and an electrolyte. The only difference between the present embodiment and the embodiment 1 is that a functional additive B as shown in Formula II-2 is added to the electrolyte. The functional additive B is N,N'-diisohexylcarbodiimide, and the addition amount is 0.3%. The rest is the same as the embodiment 1.

[0041]

[0042] Example 5 This embodiment provides an electrolyte additive and an electrolyte, which differ from Example 1 only in that a functional additive B as shown in Formula II-3 is added to the electrolyte, the functional additive B is di(trimethylsilyl)carbodiimide, and the addition amount is 0.3%. Other aspects are the same as Example 1.

[0043]

[0044] Example 6 This embodiment provides an electrolyte additive and an electrolyte, which differ from Example 1 only in that a functional additive B as shown in Formula II-4 is added to the electrolyte, and the functional additive B is 1-phenyl-3-(cyclohexylmethylene)carbodiimide, and the addition amount is 0.3%. The rest is the same as Example 1.

[0045]

[0046] Example 7 This embodiment provides an electrolyte additive and an electrolyte, which differ from Example 1 only in that a functional additive B as shown in Formula II-5 is added to the electrolyte, the functional additive B is 1,3-di-p-tolylcarbodiimide, and the addition amount is 0.3%. Other aspects are the same as Example 1.

[0047]

[0048] Example 8 This embodiment provides an electrolyte additive and an electrolyte. The only difference between the present embodiment and the embodiment 1 is that a functional additive B as shown in Formula II-6 is added to the electrolyte. The functional additive is N,N'-dicyclohexylcarbodiimide, and the addition amount is 0.3%. The rest is the same as the embodiment 1.

[0049]

[0050] Example 9 This embodiment provides an electrolyte additive and an electrolyte. The only difference between the present embodiment and the electrolyte is that a functional additive A shown in Formula I-2 is added to the electrolyte, the functional additive A is lithium trifluoromethanesulfinate, and the addition amount is 0.5%. The mass percentage of lithium hexafluorophosphate is adjusted to 12.5%. The other differences are the same as those in the electrolyte.

[0051]

[0052] Example 10 This embodiment provides an electrolyte additive and an electrolyte. The only difference between the present embodiment and the embodiment 1 is that a functional additive A shown in formula I-3 is added to the electrolyte. The functional additive A is lithium 4-methylbenzenesulfonate and the addition amount is 0.5%. The rest is the same as in the embodiment 1.

[0053]

[0054] Example 11 This example uses the electrolyte formula used in Example 1 as a reference, and uses the sulfur-containing additive included in the formula as a variable. The PS in Example 1 is adjusted to PST with an addition amount of 0.5%, and the mass percentage of lithium hexafluorophosphate is adjusted to 12.5%. Other aspects are the same as in Example 1.

[0055] Example 12 This example uses the electrolyte formula used in Example 1 as a reference, and uses the sulfur-containing additive included in the formula as a variable. The PS in Example 1 is adjusted to PST, and the addition amount is 0.7%. Other aspects are the same as Example 1.

[0056] Example 13 This example uses the electrolyte formula used in Example 1 as a reference, and uses the sulfur-containing additive included in the formula as a variable. The PS in Example 1 is adjusted to PST, and the addition amount is 1%. Other aspects are the same as Example 1.

[0057] Example 14 This example uses the electrolyte formula used in Example 1 as a reference, uses the nitrile additive included in the formula as a variable, adjusts the SN addition amount in Example 1 to 0.5%, and is otherwise the same as Example 1.

[0058] Example 15 This embodiment uses the electrolyte formula used in Example 1 as a reference, and uses the lithium salt additive included in the formula as a variable. The SN in Example 1 is adjusted to ADN, the addition amount is 0.5%, and the mass percentage of lithium hexafluorophosphate is adjusted to 14.5%. Other aspects are the same as Example 1.

[0059] Example 16 This embodiment uses the electrolyte formula used in Example 1 as a reference, and uses the lithium salt additive included in the formula as a variable. The lithium difluorophosphate in Example 1 is adjusted to lithium bis(fluorosulfonyl)imide, and the addition amount is 0.5%. Other aspects are the same as Example 1.

[0060] Comparative Example 1 This comparative example provides an electrolyte, which is the same as Example 1 except that the comparative example does not contain functional additive A and functional additive B.

[0061] Comparative Example 2 This comparative example provides an electrolyte, which is the same as Example 1 except that the comparative example does not contain the functional additive B.

[0062] The present invention provides an electrochemical device, which uses graphite as a negative electrode active material, and prepares a negative electrode slurry by mixing graphite, a conductive agent acetylene black, a binder CMC, and SBR in a mass ratio of 95.4:1.5:1.4:1.7. The negative electrode slurry is coated on a copper foil current collector and vacuum-dried to prepare a negative electrode plate. NCM622 is used as a positive electrode active material, and prepares a positive electrode slurry by mixing the positive electrode active material, a conductive agent acetylene black, and a binder PVDF in a mass ratio of 96.5:2.2:1.3. The positive electrode slurry is coated on an aluminum foil current collector and vacuum-dried to prepare a positive electrode plate. The electrolyte prepared in the embodiment and the comparative example is respectively used to assemble the positive electrode plate, the negative electrode plate, and the separator into a soft-pack battery.

[0063] NCM622 is a typical type of cathode material for ternary lithium-ion batteries, belonging to the nickel-cobalt-manganese oxide system. N stands for nickel, C for cobalt, and M for manganese. The 622 designation indicates that the molar ratio of nickel, cobalt, and manganese in the cathode material is 6:2:2.

[0064] The electrical performance of the soft pack battery was tested, and the results shown in Table 1 were obtained.

[0065] Table 1

[0066] Comparing Comparative Example 1 and Comparative Example 2, Comparative Example 1 does not contain additive A and additive B, while Comparative Example 2 contains additive A. It can be clearly seen from Table 1 that the DCR of Comparative Example 2 after the fast charge cycle is less than that of Comparative Example 1. It can be seen that the functional additive A inhibits the growth of DCR during the fast charge process and improves the fast charge cycle.

[0067] Compared with Example 1, Example 2 and Example 3 increase the content of functional additive B, and the fast charging performance is slightly deteriorated. The possible reason is that the excessive content of functional additive B increases the interface impedance, thereby deteriorating the fast charging performance. The functional additive B in the electrolyte prepared in Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7 and Example 8 meets the requirements. According to the general formula, the capacity retention rate is above 87% after 250 weeks of fast charging cycles at 2.5C, the capacity retention rate is above 94% after storage at 60℃ for 15 days, and the capacity recovery rate is above 96% after storage at 60℃ for 15 days.

[0068] The electrical performance of the soft pack battery was tested and the following results were obtained: Figure 1 The free acid content in the battery after 15 days of storage is shown. Figure 1It can be seen that compared with Comparative Example 1, Comparative Example 2 adds functional additive A, and the acidity inside the battery increases after storage. In Examples 1, 2, 3, 4, 7, and 8, the acidity is significantly reduced by adding functional additive B, which inhibits the corrosion of the positive electrode by free acid and improves high-temperature performance.

[0069] The electrical performance of the soft pack battery was tested and the following results were obtained: Figure 2 The impedance diagram after 250 cycles of fast charge cycle is shown. Comparative Example 1 does not contain functional additives A and functional additives B, and the real part impedance increases significantly after the cycle. Comparative Example 2 contains functional additive A, which directly releases Li + Compensate for the loss, form a SEI film rich in lithium fluoride and lithium sulfide at the negative electrode, and significantly reduce the real part impedance during the cycle; Example 6 contains both functional additives A and functional additives B, functional additive A forms a stable SEI film at the negative electrode, functional additive B contains -N=C=N- functional group, -N=C=N- captures H + / H2O, while Functional Additive B can effectively remove H2O / HF, blocking lithium loss caused by acid corrosion. Functional Additives A and B work synergistically to form a closed-loop "lithium replenishment-acid removal-interface stabilization" system. Their combined use effectively inhibits lithium dendrite growth and transition metal ion dissolution, stabilizing the positive electrode structure and significantly reducing post-cycle impedance compared to Comparative Example 1.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be included in the scope of protection of the present invention.

Claims

1. An electrolyte composite additive, characterized in that: Including functional additive A and functional additive B; The structural formula of functional additive A is: ； Wherein, R1 is selected from any one of halogen, substituted or unsubstituted phenyl; The structural formula of functional additive B is: ； Wherein, R2 and R3 are each independently selected from any one of a substituted or unsubstituted C2-C6 alkyl group, a substituted or unsubstituted silicon group, a substituted or unsubstituted phenyl group, and a C6-C7 cycloalkyl group.

2. The electrolyte composite additive according to claim 1, characterized in that: The electrolyte functional additive A is selected from one of the following structural formulas: 、 、 、 、 。 3. The electrolyte composite additive according to claim 1, characterized in that: The functional additive B is selected from one of the following structural formulas: 、 、 、 、 、 、 、 、 、 、 。 4. An electrolyte, characterized in that The electrolyte comprises a lithium salt and an electrolyte additive, wherein the electrolyte additive comprises the electrolyte composite additive according to any one of claims 1 to 3; Taking the total mass of the electrolyte as 100%, functional additive A accounts for (0.3~0.5)%; functional additive B accounts for (0.2~0.4)%; and lithium salt accounts for (12.5~15)%.

5. An electrolyte according to claim 4, characterized in that: Electrolyte additives also include sulfur-containing additives, nitrile additives and lithium salt additives.

6. An electrolyte according to claim 5, characterized in that: Taking the total mass of the electrolyte as 100%, the sulfur-containing additives account for (0.5-1)%, the nitrile additives account for (0.3-0.5)%, and the lithium salt additives account for (0.5-1)%.

7. An electrolyte according to claim 5, characterized in that: The sulfur-containing additive includes at least one of 1,3-propylene sultone and 1,3-propane sultone; The nitrile additive includes at least one of succinonitrile and adiponitrile; The lithium salt additive includes at least one of lithium difluorophosphate and lithium bis(fluorosulfonyl)imide.

8. An electrolyte according to claim 4, characterized in that: The electrolyte further includes an organic solvent, and the organic solvent includes fluoroethylene carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate.

9. An electrolyte according to claim 4, characterized in that: The lithium salt is lithium hexafluorophosphate.

10. A lithium-ion battery comprising a positive electrode and a negative electrode, characterized in that: It also includes the electrolyte according to any one of claims 4 to 9.

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