Electrolyte for inhibiting side reactions of battery positive electrode materials and lithium ion battery

Abstract

The present invention discloses an electrolyte for inhibiting side reactions of battery positive electrode materials, comprising a lithium salt and an organic solvent. The electrolyte further comprises: a first additive, the first additive being at least one fluorosilicone compound represented by the following formula (I): #imgabs0# wherein R1 is selected from a C1-C20 fluoroalkyl group; R2, R3, and R4 are independently selected from a C1-C20 alkyl group and a C1-C20 alkoxy group, and at least one of R2, R3, and R4 is a C1-C20 alkoxy group; and a second additive, the second additive being selected from a negative electrode film-forming additive having a reduction potential of 2.0 V or less. The electrolyte of the present invention has the advantages of inhibiting side reactions of the battery positive electrode material while improving the battery's low-temperature stability, rate stability, and long-term cycle stability.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, and in particular to an electrolyte and a lithium ion battery capable of suppressing side reactions of anode materials of the battery. Background Art

[0002] When lithium-ion batteries are cycled at high voltage, the positive and negative electrodes of the battery are prone to complex interfacial reactions with the electrolyte components, which in turn affects the battery's performance. Common negative electrode film-forming additives with a reduction potential below 2.0V, such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), lithium difluorophosphate (LiPF2O2), lithium difluorobis(oxalatophosphate) (LiDFOP), lithium difluorooxalatoborate (LiDFOB), 1,3-propane sultone (PS), 1,3-propylene sultone (PST), tris(trimethylsilyl) phosphate) (TMSP), tris(trimethylsilyl) borate (TMSB), etc., can be reduced at the negative electrode to form a solid electrolyte interface film (SEI) film, inhibiting the electrolyte-negative electrode interface reaction. Although these additives will also have film-forming reactions under high voltage, such as VC will also oxidize and form a film on the positive electrode surface, but the film is unstable, especially under high temperature conditions, which will significantly reduce the high-voltage cycle performance of the battery; FEC will produce hydrofluoric acid (HF) under high voltage, which is easy to react with lithium carbonate (Li2CO3) in the positive electrode electrolyte interface film (CEI), destroying the CEI film and promoting the dissolution of positive electrode metal ions; LiDFOP, LiDFOB, TMSB, TMSP, these additives aggravate the gas production of the battery cell under high pressure and high temperature, thereby deteriorating the high-temperature storage and high-temperature cycle performance of the battery.

[0003] Therefore, in order to suppress the side reactions of the positive electrode and improve the high-voltage cycle performance of lithium-ion batteries, the field often uses nitrile additives such as succinonitrile (SN) and adiponitrile (ADN) to the electrolyte. Nitrile additives can form complexes with metal ions in the positive electrode material, inhibit the side reactions between the electrolyte and the positive electrode, avoid the dissolution of positive electrode metal ions, and improve the high-voltage cycle performance of the battery. However, it is well known that nitrile additives have high impedance and poor compatibility with the negative electrode. When used in combination with negative electrode film-forming additives such as VC, FEC, and DTD, they produce large impedance, deteriorating the battery's rate performance, low-temperature performance, and long-term cycle stability. Some researchers have also considered using other low-impedance positive electrode film-forming protective additives, mainly to reduce lithium fluoride (LiF) to reduce impedance, such as borate additives (tripropyl borate, tributyl borate, etc.). These additives can form a film on the positive electrode and have the function of dissolving LiF, thereby effectively reducing the initial impedance of the battery. However, borate additives have poor compatibility with the negative electrode, and high-temperature storage and high-temperature cycling cause more serious gas production and impedance growth, which is not conducive to the long-term cycle of the battery.

[0004] Therefore, seeking an electrolyte that can inhibit the side reactions of the battery's positive electrode materials, have low film formation impedance, and take into account the battery's low temperature, rate and long-term cycle stability is a current technical difficulty. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention proposes a lithium-ion battery electrolyte that suppresses the side reactions of the battery's positive electrode materials and improves the battery's low-temperature, rate and long-term cycle stability.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] An electrolyte for inhibiting side reactions of a battery positive electrode material, comprising a lithium salt and an organic solvent, and further comprising:

[0008] The first additive is at least one of the fluorosilicone compounds represented by the following formula (I):

[0009]

[0010] In the formula, R1 is selected from C1-C20 fluoroalkyl; R2, R3, and R4 are independently selected from C1-C20 alkyl and C1-C20 alkoxy, and at least one of R2, R3, and R4 is C1-C20 alkoxy;

[0011] The second additive is selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), lithium difluorophosphate (LiPF2O2), lithium bis(oxalatodifluorophosphate) (LiDFOP), lithium difluorooxalatoborate (LiDFOB), 1,3-propane sultone (PS), 1,3-propylene sultone (PST), tris(trimethylsilyl) phosphate (TMSP), and tris(trimethylsilyl) borate (TMSB).

[0012] Preferably, R1 is selected from C1-C10 fluoroalkyl; R2, R3, and R4 are independently selected from C1-C4 alkyl and C1-C4 alkoxy.

[0013] More preferably, the first additive is selected from at least one of the following structures:

[0014]

[0015] In the electrolyte for suppressing side reactions of battery positive electrode materials according to the present invention, the amount of the first additive added is 0.1% to 10.0% of the total electrolyte, and the amount of the second additive added is 0.1% to 10.0% of the total electrolyte. Preferably, the amount of the first additive added is 0.2% to 3.0% of the total electrolyte, and the amount of the second additive added is 0.2% to 3.0% of the total electrolyte.

[0016] The lithium salt of the present invention can be any lithium salt commonly used in electrolytes. Preferably, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide, with a molar concentration of 0.1 to 4.0 mol / L. More preferably, the lithium salt is selected from at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, with a molar concentration of 0.8 to 1.5 mol / L.

[0017] The organic solvent of the present invention can be any organic solvent commonly used in electrolytes. Preferably, the organic solvent is selected from at least one of C3-C6 carbonates or fluorinated carbonate compounds, C3-C8 carboxylates or fluorinated carboxylates, sulfone compounds, and ether compounds.

[0018] The C3-C6 carbonate or fluorocarbonate compound is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, fluoroethylene carbonate, and difluoroethylene carbonate;

[0019] The C3-C8 carboxylic acid ester or fluorocarboxylic acid ester compound is selected from at least one of γ-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl acetate, propyl propionate, and ethyl fluoroacetate;

[0020] The sulfone compound is selected from at least one of sulfolane, dimethyl sulfoxide, dimethyl sulfone, and diethyl sulfone;

[0021] The ether compound is selected from at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,3-dioxolane, 1,4-dioxolane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0022] The first additive of the present invention can utilize the residual alkali attached to the surface of the positive electrode material (residue during the preparation process) and / or the HF remaining in the electrolyte system and / or decomposed to undergo a hydrolysis and condensation reaction with the water in the electrolyte system, thereby forming a Si-O-Si polymer protective film on the surface of the positive electrode material, thereby inhibiting the side effects of the second additive on the positive electrode material; at the same time, it can also remove moisture in the electrolyte, avoiding the hydrolysis of lithium hexafluorophosphate to produce byproducts and increase impedance.

[0023] The Si-O-Si polymer protective film has better stability, a thinner CEI and lower impedance than traditional positive electrode film-forming additives; it can not only inhibit the parasitic reaction between the electrolyte and the positive electrode material, effectively improve the high temperature and high voltage resistance of the electrolyte, but also, compared with other traditional film-forming additives, its impedance is lower, and it has no adverse effects on the low temperature and rate of the battery, and can inhibit the continuous growth of impedance during the cycle process, thereby improving the long-term cycle stability of the battery and increasing the cycle life.

[0024] Furthermore, the first additive of the present invention can also improve the electrolyte infiltration and penetrate into the gaps of the electrode. The fluorine element in the additive can also adjust the LiF content in the CEI, inhibit the side reaction of the electrolyte, further reduce the impedance, and improve the high temperature and high voltage cycle stability. At the same time, the second additive of the present invention acts on the negative electrode interface to form a film, improve the negative electrode interface cycle stability, and further ensure the cycle stability of the battery.

[0025] The present invention also provides a lithium-ion battery, which comprises a positive electrode material, a negative electrode material, a separator, and any one of the above-mentioned electrolytes.

[0026] The positive electrode material is selected from nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material or lithium cobalt oxide material.

[0027] Furthermore, the nickel-cobalt-manganese ternary material is Li(Ni x Co y Mn z )O2, x≥0.5, y>0, z>0, x+y+z=1; the nickel-cobalt-aluminum ternary material is Li(Ni x Co y Al z )O2, x≥0.8, y>0, z>0, x+y+z=1; the lithium cobalt oxide material is LiCoO2.

[0028] The negative electrode active material is selected from graphite, silicon carbon, silicon monoxide, silicon, tin, metallic lithium or a composite material thereof.

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

[0030] The present invention combines the first and second additives to suppress side reactions in the battery's positive electrode material while also addressing issues such as high impedance, high impedance growth rate, and poor high-voltage cycling stability associated with existing positive electrode film-forming additives. This improves the battery's rate, low-temperature, and long-term cycling stability. The electrolyte of the present invention is particularly suitable for high-temperature, high-voltage battery systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the LSV oxidation curve of compound 1 of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements and equivalents within the scope of the claims.

[0033] 1. Preparation of electrolyte

[0034] Preparation of basic electrolyte: In an argon-filled glove box (moisture <5 ppm, oxygen <10 ppm), ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were uniformly mixed in a mass ratio of EC:DEC:EMC = 3:2:5. Lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution until the molar concentration of LiPF6 reached 1.0 mol / L to obtain a basic electrolyte.

[0035] Example 1: 0.5% of compound 1 and 0.5% of vinylene carbonate (VC) were added to a basic electrolyte to obtain the electrolyte of this example.

[0036] Example 2: 0.5% of compound 2 and 0.5% of vinylene carbonate (VC) were added to the basic electrolyte to obtain the electrolyte of this example.

[0037] Example 3: 0.5% of compound 5 and 0.5% of vinylene carbonate (VC) were added to the basic electrolyte to obtain the electrolyte of this example.

[0038] Example 4: 0.5% of compound 6 and 0.5% of vinylene carbonate (VC) were added to the basic electrolyte to obtain the electrolyte of this example.

[0039] Example 5: 0.5% of compound 8 and 0.5% of vinylene carbonate (VC) were added to the basic electrolyte to obtain the electrolyte of this example.

[0040] Example 6: 1.0% of Compound 2 and 0.5% of vinylene carbonate (VC) were added to the basic electrolyte to obtain the electrolyte of this example.

[0041] Example 7: 1.0% of Compound 1 and 1.0% of fluoroethylene carbonate (FEC) were added to the basic electrolyte to obtain the electrolyte of this example.

[0042] Example 8: 1.0% of Compound 2 and 1.0% of fluoroethylene carbonate (FEC) were added to the basic electrolyte to obtain the electrolyte of this example.

[0043] Example 9: 1.0% of Compound 8 and 1.0% of fluoroethylene carbonate (FEC) were added to the basic electrolyte to obtain the electrolyte of this example.

[0044] Example 10: 1.0% of Compound 2 and 2.0% of fluoroethylene carbonate (FEC) were added to the basic electrolyte to obtain the electrolyte of this example.

[0045] Example 11: 1.0% of Compound 2 and 1.0% of difluoroethylene sulfate (DTD) were added to the basic electrolyte to obtain the electrolyte of this example.

[0046] Example 12: 1.0% of Compound 2 and 1.0% of lithium difluorophosphate (LiPF2O2) were added to the basic electrolyte to obtain the electrolyte of this example.

[0047] Example 13: 1.0% of Compound 2 and 1.0% of 1,3-propane sultone (PS) were added to the basic electrolyte to obtain the electrolyte of this example.

[0048] Example 14: 1.0% of Compound 2 and 1.0% of tris(trimethylsilyl)phosphate (TMSP) were added to the basic electrolyte to obtain the electrolyte of this example.

[0049] Comparative Example 1: 0.5% of Compound 2 was added to the basic electrolyte to obtain the electrolyte of this comparative example.

[0050] Comparative Example 2: 1.0% of Compound 2 was added to the basic electrolyte to obtain the electrolyte of this comparative example.

[0051] Comparative Example 3: 0.5% of Compound 8 was added to the basic electrolyte to obtain the electrolyte of this comparative example.

[0052] Comparative Example 4: 0.5% of vinylene carbonate (VC) was added to the basic electrolyte to obtain the electrolyte of this comparative example.

[0053] Comparative Example 5: 1.0% of fluoroethylene carbonate (FEC) was added to the basic electrolyte to obtain the electrolyte of this comparative example.

[0054] Comparative Example 6: 1.0% of difluoroethylene sulfate (DTD) was added to the basic electrolyte to obtain the electrolyte of this comparative example.

[0055] Comparative Example 7: 1.0% of lithium difluorophosphate (LiPF2O2) was added to the basic electrolyte to obtain the electrolyte of this comparative example.

[0056] Comparative Example 8: 1,3-propane sultone (PS) was added to the basic electrolyte to obtain the electrolyte of this example.

[0057] Comparative Example 9: 1.0% tris(trimethylsilyl)phosphate (TMSP) was added to the base electrolyte to obtain the electrolyte of this example.

[0058] Comparative Example 10: 0.5% of vinylene carbonate (VC) and 1.0% of adiponitrile (ADN) were added to the basic electrolyte to obtain the electrolyte of this comparative example.

[0059] Comparative Example 11: 0.5% of vinylene carbonate (VC) and 1.0% of succinonitrile (SN) were added to the basic electrolyte to obtain the electrolyte of this comparative example.

[0060] Comparative Example 12: 0.5% of vinylene carbonate (VC) and 1.0% of tributyl borate (TBB) were added to the basic electrolyte to obtain the electrolyte of this comparative example.

[0061] 2. Performance Testing

[0062] 1) 1.0% of compound 1 was added to the basic electrolyte and an LSV oxidation potential test was performed. Figure 1 The LSV oxidation curve is given. As shown in the figure, a preferential oxidation peak appears at around 5.0V. It is speculated that compound 1 undergoes a polymerization reaction to form a Si-O-Si polymer protective film.

[0063] 2) The lithium-ion battery electrolytes of the above embodiment and comparative example were respectively made into a soft-pack capacity 1000mAh lithium-ion power battery, wherein the lithium-ion power battery comprises a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte and battery auxiliary materials, and the positive electrode material is a nickel-cobalt-manganese ternary material (LiNi 0.83 Co 0.07 Mn 0.2 O2), the negative electrode material is graphite.

[0064] The preparation process is as follows: the positive electrode sheet, separator and negative electrode sheet are wound together into a core, sealed with aluminum-plastic film and then baked to ensure that the moisture content of the electrode meets the requirements. After baking, the battery cell is injected with electrolyte, and the finished soft-pack battery cell is obtained through the steps of standing, forming, capacity separation and aging.

[0065] The performance of the prepared lithium-ion power battery (soft-pack battery cell) was tested, and the test results are shown in Table 1 below:

[0066] Table 1 Battery performance test results

[0067]

[0068]

[0069] By comparing the test results of Examples 1 to 14 and Comparative Examples 1 to 9, it can be seen that the combined use of the first additive and the second additive is better than the use of the first additive or the second additive alone, the long-term cycle stability of the battery is the best, and the cycle life is effectively improved.

[0070] From the test results of Comparative Examples 1 to 14 and Comparative Examples 10 to 12, it can be seen that compared with the combination method of the present invention, when other positive electrode film-forming additives and the second additive are used in combination, the impedance of the battery using nitrile additives is relatively high, and the cycle stability is poor; when a low-impedance borate positive electrode film-forming additive is used in combination with the second additive, the impedance of the battery is relatively low, but the high-temperature cycle performance is poor, and still cannot meet the battery cycle life requirements.

Claims

1. An electrolyte for inhibiting side reactions of a battery positive electrode material, comprising a lithium salt and an organic solvent, characterized in that: The electrolyte further comprises: The first additive is selected from at least one of the following structures: a second additive selected from at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, lithium difluorophosphate, lithium bis(oxalatodifluorophosphate), lithium difluorooxalatoborate, 1,3-propane sultone, 1,3-propylene sultone, tris(trimethylsilyl)phosphate, and tris(trimethylsilyl)borate; The addition amount of the first additive is 0.1% to 10.0% of the total amount of the electrolyte, and the addition amount of the second additive is 0.1% to 10.0% of the total amount of the electrolyte.

2. The electrolyte for inhibiting side reactions of a battery positive electrode material according to claim 1, characterized in that: The amount of the first additive added is 0.2% to 3.0% of the total amount of the electrolyte, and the amount of the second additive added is 0.2% to 3.0% of the total amount of the electrolyte.

3. The electrolyte for suppressing side reactions of a battery positive electrode material according to claim 1, characterized in that: The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide, and has a molar concentration of 0.1 to 4.0 mol / L.

4. The electrolyte for suppressing side reactions of a battery positive electrode material according to claim 1, wherein: The organic solvent is selected from at least one of C3-C6 carbonate or fluorinated carbonate compounds, C3-C8 carboxylic acid ester or fluorinated carboxylic acid ester compounds, sulfone compounds, and ether compounds.

5. The electrolyte for inhibiting side reactions of battery positive electrode materials according to claim 4, characterized in that: The C3-C6 carbonate or fluorocarbonate compound is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; The C3-C8 carboxylic acid ester or fluorocarboxylic acid ester compound is selected from at least one of γ-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl acetate, propyl propionate, and ethyl fluoroacetate; The sulfone compound is selected from at least one of sulfolane, dimethyl sulfoxide, dimethyl sulfone, and diethyl sulfone; The ether compound is selected from at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,3-dioxolane, 1,4-dioxolane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

6. A lithium-ion battery comprising a positive electrode material, a negative electrode material, and a separator, characterized in that: The battery further comprises the lithium-ion battery electrolyte according to any one of claims 1 to 5.

7. The lithium-ion battery according to claim 6, wherein: The positive electrode material is selected from nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material or lithium cobalt oxide material.

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