An electrolyte and its application

Abstract

The present invention relates to an electrolyte and its application. The electrolyte includes a lithium salt, an organic solvent, and an additive. The electrolyte of the present invention has a relatively high conductivity at low temperatures, and the further formed lithium-ion battery has excellent low-temperature and normal-temperature performance, with a high discharge capacity retention rate at -20°C and a high capacity retention rate after 1000 cycles at 1C at 25°C.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to an electrolyte and its application. Background Art

[0002] Among secondary batteries, lithium-ion batteries have the advantages of the highest energy density, high power density, long cycle life, clean and pollution-free, etc., and have brought revolutionary changes to contemporary society in aspects such as portable electronic devices, electric vehicles, and renewable energy storage systems. However, when lithium-ion batteries are used at low temperatures, there are common problems such as low capacity, serious specific capacity attenuation, poor cycle rate performance, obvious lithium plating phenomenon, and unbalanced lithium deintercalation and intercalation, which severely restrict the application of lithium-ion batteries in low-temperature regions.

[0003] Currently, it is generally believed that the increase in electrolyte viscosity, the decrease in conductivity, and the increase in SEI film impedance at low temperatures are the main factors causing the poor low-temperature performance of lithium-ion batteries. Therefore, as the "blood" of lithium-ion batteries, the electrolyte has a significant impact on improving the low-temperature performance of lithium-ion batteries.

[0004] CN100444456C discloses a non-aqueous electrolyte for improving the low-temperature discharge performance of lithium-ion batteries and a lithium secondary battery containing the electrolyte. The disclosed non-aqueous electrolyte includes a lithium salt, a non-aqueous organic solvent, and an additive. The disclosed additive is a compound containing a sulfone group. The freezing point and viscosity of the electrolyte added with this compound are reduced, thereby effectively improving the low-temperature discharge performance of lithium-ion batteries.

[0005] CN107293776A discloses an electrolyte and a lithium-ion battery. The disclosed electrolyte includes a lithium salt, an organic solvent, and an additive containing lithium difluorophosphate and a silyl sulfate compound. The two additives can cooperate synergistically at the electrode interface of the lithium-ion battery to significantly improve the low-temperature performance of the lithium-ion battery.

[0006] Although the prior art has conducted certain research on the low-temperature performance of electrolytes, it is still crucial to develop an electrolyte with a relatively high conductivity at low temperatures, and the further formed lithium-ion battery has excellent low-temperature and normal-temperature performance. Summary of the Invention

[0007] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide an electrolyte and its application. The electrolyte has a relatively high conductivity at low temperatures, and the further formed lithium-ion battery has excellent low-temperature and normal-temperature performance, with a high discharge capacity retention rate at -20°C and a high capacity retention rate after 1000 cycles at 1C at 25°C.

[0008] To achieve this purpose, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides an electrolyte, which comprises a lithium salt, an organic solvent and an additive;

[0010] The structural formula of the additive is as shown in Formula I:

[0011]

[0012] Wherein, R1 is selected from C1-C6 alkyl groups.

[0013] In the present invention, the additive shown in Formula I is selected. In the compound shown in Formula I, the sulfonate structure can generate alkyl sulfonates with good conductivity during the charge and discharge process of the battery, which is beneficial to the formation of an organic SEI film with low impedance. At the same time, the compound shown in Formula I contains an ether bond, which is beneficial to improving the conductivity of lithium ions at the interface and improving the interface stability of the electrode material, thereby enhancing the low-temperature performance of the lithium-ion battery.

[0014] In the present invention, "C1-C6 alkyl group" refers to an alkyl group with 1-6 main-chain carbon atoms, such as C2, C3, C4, C5, etc.

[0015] Preferably, the additive comprises 3-ethoxypropyl p-toluenesulfonate and / or 2-ethoxyethyl p-toluenesulfonate.

[0016] Wherein, the structural formula of the 2-ethoxyethyl p-toluenesulfonate is as follows:

[0017]

[0018] The structural formula of the 2-ethoxypropyl p-toluenesulfonate is as follows:

[0019]

[0020] Preferably, based on the total mass of the electrolyte being 100%, the mass percentage of the additive is 0.1%-2.0%, such as 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, etc., more preferably 0.2%-0.6%, and even more preferably 0.3%.

[0021] Preferably, the electrolyte further comprises other additives.

[0022] Preferably, the other additives include any one or a combination of at least two of vinylene carbonate (VC), tris(trimethylsilyl) borate (TMSB), or divinyl sulfate (DTD). Typical but non-limiting combinations include: the combination of vinylene carbonate and tris(trimethylsilyl) borate, the combination of tris(trimethylsilyl) borate and divinyl sulfate, the combination of vinylene carbonate, tris(trimethylsilyl) borate, and divinyl sulfate, etc. Further preferably, the combination of VC, DTD, and TMSB.

[0023] Preferably, based on the total mass of the electrolyte being 100%, the mass percentage of the other additives is 0.02% - 3.2%, such as 0.05%, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5% / 3.0%, etc.

[0024] Preferably, the mass percentage of vinylene carbonate is 1.5% - 2.5%, such as 1.6%, 1.8%, 2%, 2.2%, 2.4%, etc.

[0025] Preferably, the mass percentage of tris(trimethylsilyl) borate is 0.2% - 0.5%, such as 0.3%, 0.4%, etc.

[0026] Preferably, the weight percentage of divinyl sulfate is 0.1% - 0.2%, such as 0.12%, 0.13%, 0.14%, 0.16%, 0.18%, etc.

[0027] Preferably, the lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, or lithium bis(fluorosulfonyl)imide. Typical but non-limiting combinations include: the combination of lithium hexafluorophosphate and lithium tetrafluoroborate, the combination of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and lithium perchlorate, the combination of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(pentafluoroethylsulfonyl)imide or lithium bis(fluorosulfonyl)imide, etc.

[0028] Preferably, in the electrolyte, the concentration of the lithium salt is 0.8 - 1.4 mol / L, such as 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, etc. Further preferably, it is 1 mol / L.

[0029] Preferably, the organic solvent includes any one or a combination of at least two of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl formate (MF), ethyl formate (EF), methyl acetate (MA), ethyl acetate (EA), propyl propionate (PP), ethyl butyrate (EB), ethyl propionate (EP), propyl butyrate (PB), ethylene carbonate (EC), or propylene carbonate (PC).

[0030] Preferably, the organic solvent includes any one or a combination of at least two of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), or ethyl acetate (EA). Typical but non-limiting combinations include: a combination of dimethyl carbonate and diethyl carbonate, a combination of diethyl carbonate, ethyl methyl carbonate, and ethylene carbonate, a combination of ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and ethyl acetate, a combination of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and ethyl acetate, etc. A combination of EC, DMC, EMC, and EA is further preferred.

[0031] Preferably, the mass ratio of EC, DMC, EMC, and EA is (20 - 25):(35 - 50):(10 - 30):(10 - 15). Here, 20 - 25 can be 21, 22, 23, 24, etc.; 35 - 50 can be 36, 38, 40, 42, 44, 46, 48, etc.; 10 - 30 can be 12, 14, 16, 18, 20, 22, 24, 26, 28, etc.; 10 - 15 can be 11, 12, 13, 14, etc. A ratio of 20:40:30:10 is further preferred.

[0032] In the present invention, by optimizing the organic solvent, the low-temperature conductivity of the electrolyte can be significantly improved, thereby enhancing the low-temperature conductivity performance of the lithium-ion battery formed therefrom.

[0033] In a second aspect, the present invention provides a lithium-ion battery, which includes the electrolyte described in the first aspect.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The electrolyte of the present invention has a relatively high conductivity at low temperatures. The lithium-ion battery further formed therefrom has excellent low-temperature and normal-temperature performance, a high discharge capacity retention rate at -20°C, and a high capacity retention rate after 1000 cycles at 1C at 25°C.

[0036] (2) The conductivity of the electrolyte of the present invention at -20°C is between 3.27 - 3.68 S / m, the discharge capacity retention rate at -20°C is above 75.25%, and the capacity retention rate after 1000 cycles at 1C at 25°C is above 88.22%. Detailed Embodiments

[0037] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0038] Example 1

[0039] This example provides an electrolyte, and the preparation method of the electrolyte is as follows:

[0040] (1) EC, DMC, EMC, and EA are mixed evenly in a glove box filled with inert gas according to a mass ratio of 20:40:30:10 to obtain a premixed solvent;

[0041] (2) Lithium hexafluorophosphate (LiPF6) is fully dissolved in the premixed solvent to prepare a 1 mol / L LiPF6 electrolyte, and then 2.5% by mass of VC, 0.5% of DTD, and 0.2% of TMSB are added. Finally, 0.2% of 2-ethoxyethyl p-toluenesulfonate is added, and the mixture is obtained as the electrolyte.

[0042] Example 2

[0043] This example provides an electrolyte, and the preparation method of the electrolyte is as follows:

[0044] (1) EC, DMC, EMC, and EA are mixed in a glove box filled with inert gas according to a mass ratio of 20:40:30:10 to obtain a premixed solvent;

[0045] (2) LiPF6 is fully dissolved in the premixed solvent to prepare a 1 mol / L LiPF6 electrolyte, and then 2.5% by mass of VC, 0.5% of DTD, and 0.2% of TMSB are added. Finally, 0.3% of 2-ethoxyethyl p-toluenesulfonate is added, and the mixture is obtained as the electrolyte.

[0046] Example 3

[0047] This example provides an electrolyte, and the preparation method of the electrolyte is as follows:

[0048] (1) EC, DMC, EMC, and EA are mixed in a glove box filled with inert gas according to a mass ratio of 25:35:30:10 to obtain a premixed solvent;

[0049] (2) Dissolve LiPF6 fully in the premixed solvent to prepare a 1 mol / L LiPF6 electrolyte solution, then add VC with a mass fraction of 2.5%, DTD with a mass fraction of 0.5%, and TMSB with a mass fraction of 0.2%, and finally add 2-ethoxyethyl p-toluenesulfonate with a mass fraction of 0.5%, and mix to obtain the electrolyte solution.

[0050] Example 4

[0051] This example provides an electrolyte solution, and the preparation method of the electrolyte solution is as follows:

[0052] (1) Mix EC, DMC, EMC, and EA in a mass ratio of 30:10:50:10 in a glove box filled with inert gas to obtain a premixed solvent;

[0053] (2) Dissolve LiPF6 fully in the premixed solvent to prepare a 1 mol / L LiPF6 electrolyte solution, then add VC with a mass fraction of 2.5%, DTD with a mass fraction of 0.5%, and TMSB with a mass fraction of 0.2%, and finally add 2-ethoxyethyl p-toluenesulfonate with a mass fraction of 0.3%, and mix to obtain the electrolyte solution.

[0054] Example 5

[0055] This example provides an electrolyte solution, and the preparation method of the electrolyte solution is as follows:

[0056] (1) Mix EC, DMC, EMC, and EA in a mass ratio of 30:20:30:20 in a glove box filled with inert gas to obtain a premixed solvent;

[0057] (2) Dissolve LiPF6 fully in the premixed solvent to prepare a 1 mol / L LiPF6 electrolyte solution, then add VC with a mass fraction of 2.5%, DTD with a mass fraction of 0.5%, and TMSB with a mass fraction of 0.2%, and finally add 2-ethoxyethyl p-toluenesulfonate with a mass fraction of 0.3%, and mix to obtain the electrolyte solution.

[0058] Example 6

[0059] The difference between this example and Example 2 is that 2-ethoxyethyl p-toluenesulfonate is replaced with an equal mass of 2-ethoxypropyl p-toluenesulfonate, and the rest are the same as in Example 2.

[0060] Example 7

[0061] The difference between this example and Example 2 is that DTD and TMSB are not added, and the rest are the same as in Example 2.

[0062] Comparative Example 1

[0063] This comparative example provides an electrolyte solution, and the preparation method of the electrolyte solution is as follows:

[0064] (1) Mix EC, DMC, EMC, and EA in a mass ratio of 20:40:30:10 in a glove box filled with inert gas to obtain a premixed solvent;

[0065] (2) Dissolve LiPF6 fully in the premixed solvent to prepare a 1 mol / L LiPF6 electrolyte solution, and then add VC with a mass fraction of 2.5%, DTD with 0.5%, and TMSB with 0.2%, and mix to obtain the electrolyte solution.

[0066] Comparative Example 2

[0067] This comparative example provides an electrolyte solution, and the preparation method of the electrolyte solution is as follows:

[0068] (1) Mix EC, DMC, EMC, and EA in a mass ratio of 20:40:30:10 in a glove box filled with inert gas to obtain a premixed solvent;

[0069] (2) Dissolve LiPF6 fully in the premixed solvent to prepare a 1 mol / L LiPF6 electrolyte solution, and then add VC with a mass fraction of 2.66%, DTD with 0.53%, and TMSB with 0.21%, and mix to obtain the electrolyte solution.

[0070] Performance Test

[0071] 1. Conduct the following tests on the electrolyte solutions described in Examples 1 - 7 and Comparative Examples 1 - 2:

[0072] (1) Conductivity: Use a conductivity meter to detect the conductivity. The test temperature is -20°C, and each sample measurement is carried out 3 times, and the average value is taken as the result.

[0073] 2. Inject the electrolyte solutions described in Examples 1 - 7 and Comparative Examples 1 - 2 into lithium iron phosphate soft-pack batteries. The normal-temperature capacity distribution of the lithium iron phosphate soft-pack batteries is 1.75 Ah, and prepare lithium-ion batteries for the following tests:

[0074] (1) Low-temperature discharge performance: Charge the formed lithium-ion battery at a constant current of 1C and a constant voltage to 3.65V at normal temperature, and measure the initial capacity of the battery; then place the battery in a constant-temperature oven at -20°C and discharge it at 0.5C to 2.0V, and measure the capacity retention rate of the lithium-ion battery.

[0075] (2) Normal-temperature cycle performance: Charge at a constant current of 1C and a constant voltage to 3.65V, and then discharge at a constant current of 1C to 2.5V, and cycle 1000 times to measure the capacity retention rate of the lithium-ion battery.

[0076] The test results are summarized in Table 1.

[0077] Table 1

[0078]

[0079]

[0080] Analysis of the data in Table 1 shows that the conductivity of the electrolyte of the present invention at -20°C is between 3.27 - 3.68 S / m, the discharge capacity retention rate at -20°C is above 75.25%, the capacity retention rate after 1000 cycles at 1C at 25°C is above 88.22%. The lithium-ion battery containing the electrolyte of the present invention has excellent low-temperature and normal-temperature performance, with a high discharge capacity retention rate at -20°C and a high capacity retention rate after 1000 cycles at 1C at 25°C.

[0081] Analysis of Comparative Examples 1 - 2 and Example 1 shows that the performance of Comparative Examples 1 - 2 is inferior to that of Example 2, proving that the electrolyte formed by adding the additive of the present invention has better performance.

[0082] Analysis of Example 7 and Example 2 shows that the performance of Example 7 is inferior to that of Example 2, proving that adding other additives is also beneficial to improving the performance of the electrolyte.

[0083] Analysis of Examples 1 - 3 shows that when the mass percentage of the additive in the electrolyte is 0.3%, the performance is better.

[0084] Analysis of Examples 2, 4, and 5 shows that when the solvent ratio EC:DMC:EMC:EA = 20:40:30:10, the low-temperature discharge performance is the best.

[0085] The present invention uses the above examples to illustrate the detailed method of the present invention, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of each raw material of the product of the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte includes a lithium salt, an organic solvent, and an additive; The structural formula of the additive is shown in Formula I: wherein, R1 is selected from C1-C6 alkyl; Based on the total mass of the electrolyte being 100%, the mass percentage of the additive is 0.1%-2.0%; The electrolyte further includes other additives; The other additives include any one or a combination of at least two of vinylene carbonate, tris(trimethylsilyl) borate, or ethylene sulfate; Based on the total mass of the electrolyte being 100%, the mass percentage of the other additives is 0.1%-3.2%; wherein, the mass percentage of vinylene carbonate is 1.5%-2.5%; The mass percentage of tris(trimethylsilyl) borate is 0.2%-0.5%; The weight percentage of ethylene sulfate is 0.1%-0.2%.

2. The electrolyte according to claim 1, characterized in that, The additive includes 3-ethoxypropyl p-toluenesulfonate and / or 2-ethoxyethyl p-toluenesulfonate.

3. The electrolyte according to claim 1, wherein The lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, or lithium bis(fluorosulfonyl)imide.

4. The electrolyte according to claim 1, characterized in that, In the electrolyte, the concentration of the lithium salt is 0.8-1.4 mol / L.

5. The electrolyte according to claim 1, characterized in that, The organic solvent includes any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl propionate, ethyl butyrate, ethyl propionate, propyl butyrate, ethylene carbonate, or propylene carbonate.

6. The electrolyte according to claim 5, characterized in that, The organic solvent includes any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, or ethyl acetate.

7. The electrolyte according to claim 6, characterized in that, The organic solvent includes a combination of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and ethyl acetate, wherein the mass ratio of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and ethyl acetate is (20-25):(35-50):(10-30):(10-15).

8. A lithium-ion battery, characterized in that, The lithium ion battery includes the electrolyte according to any one of claims 1-7.

Images