Lithium battery electrolyte and lithium battery

Abstract

The present invention relates to a lithium battery electrolyte. In order to obtain a high-performance lithium battery, the present invention provides a lithium battery electrolyte, the lithium battery electrolyte comprising a solvent, a lithium salt and an additive, the additive comprising an additive S, the structural formula of the additive S being: The lithium battery electrolyte of the present invention has excellent performance, can improve the normal temperature cycle performance of the lithium ion battery, inhibit gas production after high temperature storage, and improve the discharge efficiency at low temperature, and can also improve the normal temperature cycle performance of the lithium ion battery at high voltage.

Description

Technical Field

[0001] The invention relates to a lithium battery electrolyte and a lithium battery. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, high operating voltage, no memory effect, fast charge and discharge, and low environmental pollution, so they are widely used. However, with higher requirements for the energy density, safety performance and service life 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 development of the industry.

[0003] During the first charge of a lithium-ion battery, the electrolyte reacts with the carbon negative electrode to form a passivation film (SEI film). During the charge and discharge process, lithium ions must pass through the SEI film, so the SEI film has an important impact on the main performance of lithium-ion batteries (such as cycle, high temperature and power performance). The SEI film can prevent the electrolyte from further decomposing and reduce the side reactions on the negative electrode interface. However, as the charge and discharge proceed, the SEI film may dissolve, rupture, decompose, reorganize or thicken, resulting in negative effects such as increased internal resistance or gas production in the battery, thereby affecting the battery's cycle life, capacity and safety performance. These negative effects will be more serious when the battery is stored or cycled at high temperatures. In addition, as the voltage of the lithium-ion battery increases, a good passivation film (CEI film) is also required to be formed on the positive electrode side during the cycle. Due to different additives in the electrolyte or different amounts of the same additive, the quality of the formed SEI film is different, and the impedance of the film is also different. Therefore, it is very necessary to improve the quality of the SEI / CEI film by selecting appropriate additives and electrolyte formulations to achieve high-performance lithium-ion batteries. Summary of the invention

[0004] The object of the present invention is to provide a lithium battery electrolyte, which can improve the normal temperature cycle of lithium ion batteries, inhibit gas production after high temperature storage and improve discharge efficiency at low temperatures.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] A lithium battery electrolyte comprising a solvent, a lithium salt and an additive, wherein the additive comprises an additive S, and the structural formula of the additive S is Among them, R 1 is selected from substituted or unsubstituted alkyl, substituted or unsubstituted phenyl, group 1 or group 2, wherein the structural formula of group 1 is The structural formula of the group 2 is R 3 and R 4are independently selected from H, halogen or substituted or unsubstituted alkyl, R 5 is selected from substituted or unsubstituted alkyl; R 2 is selected from H, halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted alkenyl or cyano; R 6 is selected from O, substituted or unsubstituted alkyl or substituted or unsubstituted phenyl; R 7 , R 8 are each independently selected from substituted or unsubstituted alkyl groups.

[0007] Preferably, the R 1 is selected from a substituted or unsubstituted alkyl group having 1 to 3 carbon atoms, a substituted or unsubstituted phenyl group, group 1 or group 2, wherein R 3 and R 4 are independently selected from H, halogen or substituted or unsubstituted alkyl having 1 to 3 carbon atoms, wherein R 5 It is selected from substituted or unsubstituted alkyl groups having 1 to 3 carbon atoms.

[0008] Preferably, the R 2 It is selected from H, halogen, substituted or unsubstituted alkyl having 1 to 3 carbon atoms, alkoxy having 1 to 3 carbon atoms, substituted or unsubstituted alkenyl having 1 to 3 carbon atoms, or cyano.

[0009] Preferably, the R 6 It is selected from O, a substituted or unsubstituted alkyl group having 1 to 3 carbon atoms, or a substituted or unsubstituted phenyl group.

[0010] Preferably, the R 7 , R 8 Each is independently selected from a substituted or unsubstituted alkyl group having 1 to 3 carbon atoms.

[0011] More preferably, the R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 and R 8 The substituents in are independently selected from halogen, and the halogen is F.

[0012] According to some preferred embodiments, the additive S comprises

[0013]

[0014]

[0015] One or more of .

[0016] Preferably, the additive S accounts for 0.1-5% of the total mass of the lithium battery electrolyte, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, etc.

[0017] Further preferably, the additive S accounts for 2-3% of the total mass of the lithium battery electrolyte.

[0018] Preferably, the solvent includes one or more of a carbonate solvent and / or a carboxylate solvent.

[0019] Further preferably, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, and the carboxylate solvent includes one or more of ethyl acetate, propyl propionate, and ethyl butyrate.

[0020] Preferably, the solvent includes dimethyl carbonate and one or more carboxylic acid ester solvents, and the dimethyl carbonate and carboxylic acid ester solvents account for 10-30% of the total mass of the lithium battery electrolyte, for example, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, etc.

[0021] According to some preferred embodiments, the solvent includes ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl acetate and ethyl methyl carbonate.

[0022] According to other preferred embodiments, the solvent includes ethylene carbonate, propylene carbonate, dimethyl carbonate, propyl propionate and ethyl methyl carbonate.

[0023] According to some further preferred embodiments, the solvent includes ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl butyrate and ethyl methyl carbonate.

[0024] Preferably, the lithium salt is selected from LiClO 4 、LiPF 6 , LiTFSI, LiFSI or more.

[0025] Preferably, the lithium salt accounts for 10-20% of the total mass of the lithium battery electrolyte, for example, 10%, 12%, 14%, 16%, 18%, 20%, etc.

[0026] Preferably, the additive further comprises one or more of fluoroethylene carbonate, nitrile compounds, lithium difluorophosphate, sulfur-containing compounds, and acid anhydride compounds. The nitrile compounds include but are not limited to hexanetrinitrile, the sulfur-containing compounds include but are not limited to 1,3-propane sultone, and the acid anhydride compounds include but are not limited to succinic anhydride.

[0027] The present invention also provides a lithium battery, which includes the lithium battery electrolyte as described above.

[0028] Preferably, the positive electrode in the lithium battery comprises a nickel-cobalt-manganese ternary material or a lithium cobalt oxide material; and the negative electrode in the lithium battery comprises graphite or a SiOx@C composite material.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] The lithium battery electrolyte in the present invention has excellent performance, can improve the room temperature cycle performance of the lithium ion battery, inhibit gas production after high temperature storage and improve the discharge efficiency at low temperature, and can also improve the room temperature cycle performance of the lithium ion battery under high voltage. DETAILED DESCRIPTION

[0031] In order to improve the room temperature, high temperature and low temperature performance of lithium batteries, the present invention provides a lithium battery electrolyte. The lithium battery electrolyte includes a solvent, a lithium salt and an additive, wherein the additive includes an additive S, and the structural formula of the additive S is

[0032]

[0033] Among them, R 1 is selected from substituted or unsubstituted alkyl, substituted or unsubstituted phenyl, group 1 or group 2, wherein the structural formula of group 1 is The structural formula of the group 2 is R 3 and R 4 are independently selected from H, halogen or substituted or unsubstituted alkyl, R 5 is selected from substituted or unsubstituted alkyl;

[0034] R 2 is selected from H, halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted alkenyl or cyano;

[0035] R 6 is selected from O, substituted or unsubstituted alkyl or substituted or unsubstituted phenyl;

[0036] R 7 , R 8 are each independently selected from substituted or unsubstituted alkyl groups.

[0037] The present invention is further described in detail below in conjunction with specific embodiments. The following is a preferred embodiment of the present invention. It should be noted that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the embodiments of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

[0038] Unless otherwise specified, the additive S in the following embodiments and comparative examples includes:

[0039]

[0040]

[0041] Comparative Example 1 and Examples 1-24

[0042] Electrolyte: EC (ethylene carbonate) / PC (propylene carbonate) / DMC (dimethyl carbonate) / EA (ethyl acetate) / EMC (ethyl methyl carbonate) / LiPF 6 (lithium hexafluorophosphate) = 25 / 5 / 20 / 10 / 25 / 15 (mass ratio), other components and amounts in the electrolyte are shown in Table 1.

[0043] Positive electrode: NCM811, negative electrode: graphite.

[0044] The electrolyte, positive electrode and negative electrode are assembled into a lithium battery according to conventional processes. The lithium batteries prepared in each embodiment are tested. At 25°C, the battery is charged to 4.2V with a current of 0.1C and then left for 5 minutes; the battery is discharged to 2.8V with a current of 0.1C and left for 5 minutes. After the battery is formed, at 25°C, the battery is charged to 4.2V with a current of 1C and then left for 5 minutes; the battery is discharged to 2.8V with a current of 1C and left for 5 minutes, and the above steps are repeated 300 times;

[0045] The electrolyte, positive electrode and negative electrode were assembled into lithium batteries according to conventional processes. The lithium batteries prepared in various embodiments were tested. At 25°C, the batteries were charged to 4.2V at a current of 0.1C and then left for 5 minutes. The batteries were discharged to 2.8V at a current of 0.1C and left for 5 minutes. After the batteries were formed, they were charged to 4.2V at a current of 0.2C. At the same time, the swelling rate of the lithium batteries prepared in various embodiments was tested after being left for 30 days at a high temperature of 60°C. The results are shown in Table 1.

[0046] Table 1

[0047]

[0048]

[0049] Examples 25-30 and Comparative Example 2

[0050] The difference from Example 1 is that the components of the electrolyte are different. The components and amounts of the electrolyte are detailed in Table 2.

[0051] The electrolyte, positive electrode and negative electrode are assembled into a lithium battery according to conventional processes. The lithium batteries prepared in each embodiment are tested. At 25°C, the battery is charged to 4.2V with a current of 0.1C and then left for 5 minutes; the battery is discharged to 2.8V with a current of 0.1C and left for 5 minutes. After the battery is formed, at 25°C, the battery is charged to 4.2V with a current of 1C and then left for 5 minutes; the battery is discharged to 2.8V with a current of 1C and left for 5 minutes, and the above steps are repeated 300 times;

[0052] The electrolyte, positive electrode and negative electrode were assembled into lithium batteries according to conventional processes. The lithium batteries prepared in various embodiments were tested. At 25°C, the batteries were charged to 4.2V at a current of 0.1C and then left for 5 minutes. The batteries were discharged to 2.8V at a current of 0.1C and left for 5 minutes. After the batteries were formed, they were charged to 4.2V at a current of 0.2C. At the same time, the swelling rate of the lithium batteries prepared in various embodiments was tested after being left at a high temperature of 60°C for 30 days.

[0053] The electrolyte, positive electrode and negative electrode were assembled into lithium batteries according to conventional processes. The lithium batteries prepared in each embodiment were tested. At 25°C, the batteries were charged to 4.2V at 0.1C current and then left for 5 minutes; the batteries were discharged to 2.8V at 0.1C current and left for 5 minutes. After the batteries were formed, they were charged to 4.2V at 0.2C current; and the lithium batteries prepared in each embodiment were tested at low temperature of -20°C and discharged to 2.8V at 0.2C. The results are shown in Table 2.

[0054] Table 2

[0055]

[0056]

[0057] Among them, PP in Table 2 is propyl propionate and EB is ethyl butyrate.

[0058] Comparative Example 3 and Examples 31-42

[0059] Electrolyte: EC / PC / DMC / EA / EMC / LiPF 6 =25 / 5 / 20 / 10 / 25 / 15 (mass ratio); the electrolyte also includes additives, the additives include 5wt% FEC (fluoroethylene carbonate), 2wt% HTCN (hexane trinitrile), 1wt% LiPF 2 O 2 (lithium difluorophosphate) and additive S. The composition and amount of additive S are shown in Table 3.

[0060] Positive electrode: 4.4V LCO; Negative electrode: SiOx@C material.

[0061] The electrolyte, positive electrode and negative electrode were assembled into lithium batteries according to conventional processes. The lithium batteries prepared in various embodiments were tested. At 25°C, the batteries were charged to 4.4V at 0.1C current and then left for 5 minutes; the batteries were discharged to 2.8V at 0.1C current and left for 5 minutes. After the batteries were formed, at 25°C, the batteries were charged to 4.4V at 1C current and then left for 5 minutes; the batteries were discharged to 2.8V at 1C current and left for 5 minutes. The above steps were repeated 300 times.

[0062] The electrolyte, positive electrode and negative electrode were assembled into lithium batteries according to conventional processes. The lithium batteries prepared in various embodiments were tested. At 25°C, the batteries were charged to 4.4V at a current of 0.1C and then left for 5 minutes. The batteries were discharged to 2.8V at a current of 0.1C and left for 5 minutes. After the batteries were formed, they were charged to 4.4V at a current of 0.2C. At the same time, the swelling rate of the lithium batteries prepared in various embodiments was tested after being left at a high temperature of 60°C for 7 days.

[0063] See Table 3 for the results.

[0064] Table 3

[0065]

[0066] Comparative Examples 4-6 and Examples 43-45

[0067] The difference from Example 31 is that the components of the additives are different. The components and amounts of the additives are detailed in Table 4.

[0068] The electrolyte, positive electrode and negative electrode were assembled into lithium batteries according to conventional processes. The lithium batteries prepared in various embodiments were tested. At 25°C, the batteries were charged to 4.4V at 0.1C current and then left for 5 minutes; the batteries were discharged to 2.8V at 0.1C current and left for 5 minutes. After the batteries were formed, at 25°C, the batteries were charged to 4.4V at 1C current and then left for 5 minutes; the batteries were discharged to 2.8V at 1C current and left for 5 minutes. The above steps were repeated 300 times.

[0069] The electrolyte, positive electrode and negative electrode were assembled into lithium batteries according to conventional processes. The lithium batteries prepared in various embodiments were tested. At 25°C, the batteries were charged to 4.4V at a current of 0.1C and then left for 5 minutes. The batteries were discharged to 2.8V at a current of 0.1C and left for 5 minutes. After the batteries were formed, they were charged to 4.4V at a current of 0.2C. At the same time, the swelling rate of the lithium batteries prepared in various embodiments was tested after being left at a high temperature of 60°C for 7 days.

[0070] See Table 4 for the results.

[0071] Table 4

[0072]

[0073] Among them, PS in Table 4 is 1,3-propane sultone; SA is succinic anhydride.

[0074] The above detailed description of the present invention is intended to enable persons familiar with the art to understand the contents of the present invention and implement them. It does not limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium battery electrolyte, which is composed of a solvent, a lithium salt and an additive, characterized in that: The additives include additives S, the additives S are selected from , 、 One or more of the following, wherein the additive S accounts for 0.1-5% of the total mass of the lithium battery electrolyte; The solvent is composed of one or more of carbonate solvents and / or carboxylate solvents.

2. The lithium battery electrolyte according to claim 1, characterized in that: The carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate; the carboxylate solvent includes one or more of ethyl acetate, propyl propionate, and ethyl butyrate.

3. The lithium battery electrolyte according to claim 1, characterized in that: The solvent includes dimethyl carbonate and one or more carboxylic acid ester solvents, and the dimethyl carbonate and carboxylic acid ester solvents account for 10-30% of the total mass of the lithium battery electrolyte.

4. The lithium battery electrolyte according to claim 1, characterized in that: The lithium salt is selected from one or more of LiClO4, LiPF6, LiTFSI, and LiFSI; and / or, The lithium salt accounts for 10-20% of the total mass of the lithium battery electrolyte.

5. The lithium battery electrolyte according to claim 1, characterized in that: The additives also include one or more of fluoroethylene carbonate, nitrile compounds, lithium difluorophosphate, sulfur-containing compounds, and acid anhydride compounds.

6. A lithium battery, characterized in that: The lithium battery comprises the lithium battery electrolyte according to any one of claims 1 to 5.

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