Non-aqueous electrolyte and secondary battery

Abstract

The application discloses a nonaqueous electrolyte and a secondary battery; the nonaqueous electrolyte comprises a solvent, a metal salt and an additive; the additive comprises a benzene structure additive with at least one of the following structures and TMP; wherein R1, R2, R3 and R4 are respectively selected from one of H, F, Cl, Br, a hydroxyl group and C1-10 alkyl. Trimethyl phosphite is used in the electrolyte, and a specific structure additive combination is introduced; the NH or =N structure in the benzene structure can be coupled with the -O- structure in the TMP; after benzene dehydrogenation or open bond, the -N-O acid salt or -N-O-P phosphorus nitrogen acid salt is formed with the TMP, can more effectively repair the SEI film for a long time, maintain the long life cycle of the cycle and storage performance, and inhibit the gas production in the long-term use process of the battery; and the overall performance of the battery in the long life cycle is comprehensively improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of battery materials, and relates to a non-aqueous electrolyte and a secondary battery. BACKGROUND

[0002] Secondary batteries have the characteristics of large capacity, fast charging speed, high energy density, long cycle life, etc., and have been widely used in daily life and production equipment, such as consumer electronics, new energy electric vehicles, household and industrial and commercial energy storage products. A large number of academic researches and industrial researches have found that the static storage decay and dynamic cycle decay of the battery in a high-temperature environment are strongly related to the residual water content in the battery, the stability of the SEI film of the negative electrode, and the side reaction of the full intercalation negative electrode and the electrolyte, which can cause the loss of active lithium, the damage of the SEI film, and the intensification of the side reaction, and can also be accompanied by the release of gas to cause the expansion of the battery cell, thereby degrading the performance of the battery and greatly reducing the overall service life of the battery.

[0003] The prior art usually uses various additives to improve the construction and maintenance of the SEI film and the long cycle performance of the battery. The use of different additives can greatly improve the composition of SEI / CEI, and improve the cycle life, such as vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, 1,3-propane sulfone lactone, and methane disulfide methylene ester. However, the SEI film formed by the above-mentioned many kinds of additives still has some defects, and cannot effectively inhibit the peeling and decomposition of the SEI, nor can it inhibit the side reaction caused by residual water molecules. Therefore, it is crucial to develop an additive with excellent high-temperature performance and long cycle performance and its non-aqueous electrolyte.

[0004] Through the search of the prior patent documents, it is found that CN1819324A provides a kind of electrolyte for lithium ion battery, and the functional additive in the electrolyte includes benzotriazole compound and at least one of vinyl ethylene carbonate, vinylene carbonate, cyclic sulfonic acid, cyclic sulfate, cyclic sulfite, cyclic anhydride and cyclic imide. The lithium ion battery prepared by using the electrolyte can improve the mechanism of the electrolyte during battery formation, reduce the gas emission, improve the storage life of the battery, and show high capacity and excellent charge / discharge cycle performance. However, the simple benzotriazole compound or the combination in CN1819324A can only reduce the gas emission during the formation stage. The effect of continuously inhibiting gas emission is limited during the long-term cycle use and storage of the battery, and it is difficult to repair the peeled and damaged SEI film during the cycle, and it is difficult to maintain the overall performance during the long service life. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a non-aqueous electrolyte and a secondary battery.

[0006] The object of the present application is achieved by the following technical solutions:

[0007] The present application provides a non-aqueous electrolyte for secondary batteries, comprising a solvent, a metal salt, and an additive; the additive comprises a benzene structure type additive, which is at least one of the following structures:

[0008]

[0009] In the above structure, R1, R2, R3, and R4 can be H, F, Cl, Br, hydroxyl, one of methyl to decyl.

[0010] As an embodiment, the additive further comprises trimethyl phosphite. That is, in the electrolyte, the additive comprises trimethyl phosphite (TMP), and at least one of structure 1, structure 2, structure 3, and structure 4.

[0011] As an embodiment, in the electrolyte, the content of the benzene structure type additive is 0.01-1 wt.%.

[0012] As an embodiment, in the electrolyte, the content of the trimethyl phosphite is 0.01-1 wt.%. Preferably, the content is 0.02-0.5 wt.%.

[0013] As an embodiment, in the electrolyte, the usage ratio of the benzene structure type additive to the trimethyl phosphite is 1:100-100:1.

[0014] As an embodiment, the metal salt is a lithium salt, and the content of the lithium salt in the electrolyte is 7-18 wt.%.

[0015] As an embodiment, the metal salt is a lithium salt, and the lithium salt comprises any one or a combination of at least two of LiPF6, LiPO2F2, LiFSI, LiFSA, LiBF4, LiODFP, LiODFB, LiAsF6, LiTFSI, and the content is 7-18 wt.%.

[0016] As an embodiment, the metal salt is a sodium salt, and the content of the sodium salt in the electrolyte is 5-18 wt.%.

[0017] As an embodiment, the metal salt is a sodium salt, and the sodium salt comprises at least one of NaPF6, NaPO2F2, NaFSI, NaBF4, NaODFP, NaODFB, and NaTFSI.

[0018] As an embodiment, the metal salt is a potassium salt, and the content of the potassium salt in the electrolyte is 3-18 wt.%.

[0019] As an embodiment, the metal salt is a potassium salt, which comprises at least one of KPF6, KPO2F2, KFSI, KBF4, KODFP, KODFB, and KTFSI.

[0020] As an embodiment, the solvent comprises a combination of at least two of EC, PC, DMC, EMC, DEC, EA (ethyl acetate), EP, PP, MA, and MP.

[0021] As an embodiment, the solvent content in the electrolyte is 70-88 wt.%.

[0022] As an embodiment, the electrolyte can further comprise a negative electrode film-forming additive, which comprises at least one or a combination of more than one of VC, FEC (fluoroethylene carbonate), DTD (vinyl sulfate), MMDS (methyl methylene disulfonate), and PS (1,3-propane sultone).

[0023] As an embodiment, the electrolyte can further comprise a positive electrode film-forming additive, which comprises any one or a combination of more than one of TMSP (tris(trimethylsilyl)phosphate) and TMSB (TMSB).

[0024] In another aspect, a secondary battery using the aforementioned non-aqueous electrolyte also falls within the scope of the present application.

[0025] As an embodiment, the secondary battery is a lithium battery system; the active material in the positive electrode is any one or a combination of more than one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese phosphate, lithium cobalt phosphate, and lithium nickel cobalt manganese aluminum phosphate. Sodium batteries, potassium batteries, and the like can also be used correspondingly, provided that the lithium salt is replaced by a sodium salt or a potassium salt.

[0026] As an embodiment, the secondary battery is a lithium battery system; the active material in the negative electrode is any one or a combination of more than one of graphite and silicon-containing material.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] 1) The present application introduces a specific structural additive combination in the electrolyte. The N in the benzene structure and the O, P in the TMP can complex the transition metal dissolution on the positive and negative sides, further reducing the deposition of transition metals in long-term cycling and storage, and improving the stability of the negative SEI. On the positive side, under high pressure, it can complex with the positive metal, then form a stable CEI, further protect the positive material, and prevent degradation.

[0029] 2) The present application introduces a specific structure additive combination in the electrolyte, after ring opening, the structure can generate a film composition containing complex nitrate, nitrite, phosphate, N-P organic matter, improve the original SEI composition, improve the negative electrode interface, and inhibit lithium precipitation.

[0030] 3) The present application uses trimethyl phosphite in the electrolyte, trimethyl phosphite has a lone pair of electrons on the phosphorus; while introducing a specific structure additive combination, the NH or =N structure in the benzene structure can couple with the -O- structure in TMP, after benzene dehydrogenation or ring opening, form -N-O acid salt or -N-O-P phosphorus nitrogen salt with TMP, which can improve the SEI composition during long-term cycling and storage of the battery, more effectively repair the SEI film for a long period of time, maintain the long cycle life and storage performance, and inhibit gas production during long-term use of the battery; overall improve the overall performance of the battery during the long cycle life. DETAILED DESCRIPTION

[0031] The present application will be described in detail below with reference to the examples. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of adjustments and improvements can be made. These all belong to the protection scope of the present application.

[0032] Example 1

[0033] A lithium iron phosphate battery system was used, the electrolyte formula was 1.1M LiPF6 in EC / DMC / EMC (2:3:3 v / v / v), and the additives were 3.5wt.% VC, 0.5wt.% FEC, 0.3wt.% TMP, and the additive of structure 4

[0034] The additive (benzotriazole) had a content of 0.3wt.%.

[0035] Example 2

[0036] A lithium iron phosphate battery system was used, the electrolyte formula was 1.1M LiPF6 in EC / DMC / EMC (2:3:3 v / v / v), and the additives were 3.5wt.% VC, 0.5wt.% FEC, 0.3wt.% TMP, and the additive of structure 2, wherein R2, R3, R4 were all methyl, The additive was 1-(trimethylsilyl)benzotriazole, and the content was 0.3wt.%.

[0037] Example 3

[0038] Using a lithium iron phosphate battery system, electrolyte formulation was 1.1 M LiPF6 in EC / DMC / EMC (2:3:3 v / v / v) with 3.5 wt.% VC, 0.5 wt.% FEC, 0.3 wt.% TMP, and an additive of Structure 1,

[0039] wherein R1 is hydroxyl; i.e., the additive is 1 -hydroxybenzotriazole at 0.3 wt.%.

[0040] Example 4

[0041] Using a lithium iron phosphate battery system, electrolyte formulation was 1.1 M LiPF6 in EC / DMC / EMC (2:3:3 v / v / v) with 3.5 wt.% VC, 0.5 wt.% FEC, 0.3 wt.% trimethyl phosphate, and an additive of Structure 4 (benzotriazole) at 0.3 wt.%.

[0042] Example 5

[0043] Using a lithium iron phosphate battery system, electrolyte formulation was 1.1 M LiPF6 in EC / DMC / EMC (2:3:3 v / v / v) with 3.5 wt.% VC, 0.5 wt.% FEC, 0.3 wt.% TMP, and an additive of Structure 1, wherein R2 is H and R1 is phenyl The specific material was 1 -benzyl- 1 H-benzotriazole (CAS: 4706-43-8) at 0.3 wt.%.

[0044] Example 6

[0045] Using a lithium iron phosphate battery system, electrolyte formulation was 1.1 M LiPF6 in EC / DMC / EMC (2:3:3 v / v / v) with 3.5 wt.% VC, 0.5 wt.% FEC, and an additive of Structure 4 (benzotriazole) at 0.3 wt.%.

[0046] Example 7

[0047] Using a lithium iron phosphate battery system, electrolyte formulation was 1.1 M LiPF6 in EC / DMC / EMC (2:3:3 v / v / v) with 3.5 wt.% VC, 0.5 wt.% FEC, and 0.3 wt.% TMP.

[0048] Example 8

[0049] Using lithium iron phosphate battery system, electrolyte formula is 1.1M LiPF6, EC, DMC, EMC in volume ratio of 2:3:3, additives are 3.5wt.% VC, 0.5wt.% FEC, 0.1wt.% TMP, and additives of structure 4

[0050] The additive is benzotriazole, and the content is 0.1wt.%.

[0051] Example 9

[0052] Using lithium iron phosphate battery system, electrolyte formula is 1.1M LiPF6, EC, DMC, EMC in volume ratio of 2:3:3, additives are 3.5wt.% VC, 0.5wt.% FEC, 1wt.% TMP, and additives of structure 4

[0053] The additive is benzotriazole, and the content is 1wt.%.

[0054] The electrolyte of examples 1-9 is applied to lithium iron phosphate battery system for performance test, and the performance comparison is shown in the following table 1. Among them, the positive electrode slurry ratio is lithium iron phosphate: conductive carbon black (Super P): binder (polyvinylidene fluoride PVDF_5130): dispersing agent (polyvinylpyrrolidone PVP_30) = 97.15:1.1:1.6:0.15.

[0055] The negative electrode slurry ratio is graphite: conductive agent (Super P): binder (styrene butadiene rubber SBR): binder (carboxymethyl cellulose lithium CMC_Li) = 96.1:1:1.8:1.1.

[0056] Then coating, the positive electrode slurry is coated on the aluminum foil, and the negative electrode slurry is coated on the copper foil, and drying and winding are carried out. Then rolling is carried out, and then die cutting is carried out. Then the production of laminated core is carried out, using the produced positive and negative electrode sheets and the separator, and the separator adopts PE separator (7μm base film+2μm Al2O3 ceramic layer+1μm PVDF glue layer). After the lamination of the core, the lug is welded, and then assembled into an aluminum plastic film to form a soft package dry cell.

[0057] After the dry cell is baked, the injection is carried out, and the injection amount is calculated according to the injection coefficient*the design capacity of the cell, and the injection coefficient is 3.6g / Ah, and the design capacity of the cell is 8.7Ah, so the injection amount of single cell is 31.32±0.5g. After the battery is infiltrated, formation and capacity distribution are carried out to obtain finished cells.

[0058] High temperature cycle test method:

[0059] 1. The battery is placed in a 55℃ constant temperature cabinet until the temperature is balanced and the battery is heated to the specified temperature;

[0060] 2.1C CCCV charged to 3.65V, 0.05C current cut-off;

[0061] 3. Rest for 30min;

[0062] 4. 1C discharge to 2.0V;

[0063] 5. Rest for 30min;

[0064] 6. Cycle test as above steps;

[0065] 7. Check the capacity retention at 500 cycles.

[0066] High temperature storage test method:

[0067] 1. At room temperature 25℃ constant temperature cabinet conditions, the battery is charged to 3.65V with 1C CCCV, 0.05C current cut-off; 2. The battery is put into 60℃ oven for storage for 30 days;

[0068] 3. The battery is placed in a constant temperature cabinet at room temperature 25℃ for 4h;

[0069] 4. Test the gas production of the battery;

[0070] 5. 1C discharge to 2.0V, record as capacity retention.

[0071] 2.2C fast charging and lithium precipitation determination method:

[0072] 1. The battery is placed in a constant temperature cabinet at 25℃ until the temperature is balanced and the battery is heated to the specified temperature;

[0073] 2. 1C discharge to 2.0V;

[0074] 3. Rest for 30min;

[0075] 4. 2.2C CC charged to 3.65V;

[0076] 5. Rest for 30min;

[0077] 6. Cycle test as above steps;

[0078] 7. When cycled to 50 cycles, the battery is taken out and disassembled in a dry room, the electrode is unfolded, and the lithium precipitation on the full-embedded negative electrode is observed.

[0079] Table 1

[0080]

[0081]

[0082] As can be seen from Table 1, compared with Example 1, the gas production of Example 4 at 60 DEG C 100% SOC storage for 30D is significantly increased, the retention rate at 55 DEG C high temperature cycle for 500 cycles, the capacity retention rate at 60 DEG C 100% SOC storage for 30D is significantly reduced, and large-area lithium precipitation occurs at 2.2C fast charging for 50 cycles; the reason may be that the additive trimethyl phosphate is P=O structure, which is difficult to form an electron-donating group. Compared with Example 1, the same as Example 5, the gas production at 60 DEG C 100% SOC storage for 30D is significantly increased, the retention rate at 55 DEG C high temperature cycle for 500 cycles, the capacity retention rate at 60 DEG C 100% SOC storage for 30D is significantly reduced, and large-area lithium precipitation occurs at 2.2C fast charging for 50 cycles; the reason may be that the N in the structural formula of the additive of Example 5 is connected with the benzene ring, so that the coupling difficulty with the -O- structure in TMP is increased. The performance comparison of Example 6, 7 and Example 1 shows that in the system of the application, by introducing a specific structural additive combination while using trimethyl phosphite, the SEI film can be effectively repaired in the long-term cycle and storage process of the battery, the long-life cycle and storage performance can be maintained, and the gas production in the long-term use process of the battery can be inhibited.

[0083] The specific embodiments of the application are described above. It should be understood that the application is not limited to the specific embodiments described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the application.

Claims

1. A non-aqueous electrolyte for secondary batteries, comprising a solvent, a metal salt, and an additive; said additive comprising a benzo[a]-type additive, having at least one of the following structures: 、 、 、 ； in, R1, R2, R3 and R4 are selected from one of H, F, Cl, Br, hydroxyl, and C1-10 alkyl groups, respectively; The additive also includes trimethyl phosphite; the content of benzo[a]-type additives in the electrolyte is 0.01-1 wt.%, and the content of trimethyl phosphite is 0.01-1 wt.%.

2. The non-aqueous electrolyte according to claim 1, characterized in that, In the electrolyte, the ratio of benzo[a]-type additives to trimethyl phosphite is 1:100-100:

1.

3. The non-aqueous electrolyte according to claim 1, characterized in that, It also includes at least one of the following technical features: A. The metal salt is a lithium salt, and the lithium salt content in the electrolyte is 7-18 wt.%. B. The metal salt is a lithium salt, and the lithium salt includes at least one of LiPF6, LiPO2F2, LiFSI, LiFSA, LiBF4, LiODFP, LiODFB, LiAsF6, and LiTFSI; C. The metal salt is a sodium salt, and the sodium salt content in the electrolyte is 5-18 wt.%. D. The metal salt is a sodium salt, and the sodium salt includes at least one of NaPF6, NaPO2F2, NaFSI, NaBF4, NaODFP, NaODFB, and NaTFSI; E. The metal salt is a potassium salt, and the potassium salt content in the electrolyte is 3-18 wt.%. F. The metal salt is a potassium salt, and the potassium salt contains at least one of KPF6, KPO2F2, KFSI, KBF4, KODFP, KODFB, and KTFSI; G. The solvent comprises a combination of at least two of EC, PC, DMC, EMC, DEC, EA, EP, PP, MA, and MP; H. The solvent content in the electrolyte is 70-88 wt.%.

4. The non-aqueous electrolyte according to claim 1, characterized in that, The additives also include negative electrode film-forming additives; the negative electrode film-forming additives include at least one of VC, FEC, DTD, MMDS, and PS.

5. The non-aqueous electrolyte according to claim 1, characterized in that, The additives also include positive electrode film-forming additives; the positive electrode film-forming additives include at least one of TMSP and TMSB.

6. A secondary battery using the non-aqueous electrolyte of claim 1.

7. The secondary battery according to claim 6, characterized in that, The active material in the negative electrode of the secondary battery is at least one of graphite and silicon-containing materials.

8. The secondary battery according to claim 6, characterized in that, The secondary battery is a lithium battery system; the active material in the positive electrode is at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt phosphate, and lithium nickel cobalt manganese aluminum oxide.

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