CN111384441A - A battery electrolyte additive and electrolyte and lithium ion battery containing the additive - Google Patents

Abstract

The invention provides an additive applied to battery electrolyte, which has the structure shown in the following (I),

the substituents are shown in the specification. The invention also provides an electrolyte and a battery using the additive. The additive provided by the invention can effectively reduce the interface impedance and charge transfer impedance between negative electrode materials such as graphite, silicon carbon and the like and electrolyte, and further effectively improve the cycle stability and rate capability of the negative electrode materials.

Description

A battery electrolyte additive and electrolyte and lithium ion containing the additive Battery

technical field

The invention belongs to the field of lithium ion battery electrolyte, and relates to an additive for lithium ion battery electrolyte and an electrolyte and lithium ion battery using the additive.

Background technique

Lithium-ion batteries have the advantages of high energy density, long cycle life, high operating voltage, low self-discharge and no memory effect, and are widely used in 3C, energy storage and power batteries. Longer cycle life, higher energy density, faster rate performance, wider operating temperature and lower price and cost are important directions for the development of lithium-ion batteries.

Electrolyte is one of the key materials of lithium-ion batteries. Its function is to conduct lithium ions between the positive electrode and the negative electrode, which will have an important impact on the rate performance, cycle life, and temperature window of the battery. Lithium ion electrolyte is mainly composed of three parts: solvent, lithium salt and additives. The additives are divided into negative electrode film-forming additives, water removal additives, positive electrode film-forming additives, additives for improving conductivity, additives for improving wettability and additives according to different functions. Flame retardant additives, etc.

As far as the negative electrode film-forming additive is concerned, when it is applied to a lithium-ion battery, during the first charging process of the lithium-ion battery, the negative electrode film-forming additive undergoes reduction and decomposition before the electrolyte solvent, and the generated product is deposited on the negative electrode surface to form a passivation layer. , also known as SEI (Solid electrochemical interface) film. The SEI film only allows lithium ions to pass through, which can not only effectively inhibit the insertion of solvated lithium ions between the graphite layers, thereby preventing the exfoliation of graphite, but also effectively inhibit the side reactions between the negative electrode and the electrolyte, thereby improving the cycle stability of lithium batteries. . In addition, the SEI film also has an important influence on the electrical conductivity, temperature performance, etc.

In the prior art, the typical negative film-forming additives that have been reported are vinylene carbonate (VC), ethylene ethylene carbonate (VEC), 1,3-propane sultone (PS) and fluoroethylene carbonate. (FEC), etc. Although these anode film-forming additives can improve the cycle performance of the battery anode, there are still problems in the improvement of high temperature and rate performance.

Therefore, it is necessary to conduct further research on anode film-forming additives for Li-ion batteries.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a battery electrolyte additive, the battery electrolyte additive has the following structural formula (I):

in:

R1, R2, R3, R4, R5 are independently selected from C1-C20 alkyl, C2-C20 alkenyl, C1-C20 alkoxy, C1-C20 haloalkyl, C2-C20 haloalkenyl, C1-C20 haloalkane Oxygen.

The compound represented by the structural formula (I) provided by the present invention, its substituents R1, R2, R3, R4, R5 are independently selected from C1-C20 alkyl, C2-C20 alkenyl, C1-C20 alkoxy, C1- C20 haloalkyl, C2-C20 haloalkenyl, C1-C20 haloalkoxy.

Preferably, the substituents R1, R2, R3, R4 and R5 are independently selected from C1-C12 alkyl, C2-C12 alkenyl, C1-C12 alkoxy, C1-C12 haloalkyl, C2-C12 halo Alkenyl, C1-C12 haloalkoxy.

Further preferably, the substituents R1, R2, R3, R4 and R5 are independently selected from C1-C5 alkyl, C2-C5 alkenyl, C1-C5 alkoxy, C1-C5 haloalkyl, C2-C5 Haloalkenyl, C1-C5 haloalkoxy.

More preferably, the substituents R1, R2, R3, R4, and R5 are independently selected from C1-C5 alkyl and C1-C5 haloalkyl.

Most preferably, the substituents R1, R2, R3, R4, R5 are independently selected from C1-C3 alkyl, C1-C3 haloalkyl.

The battery electrolyte additive represented by the structural formula (I) provided by the present invention is suitable for use as a negative electrode film-forming additive in the battery electrolyte.

When the compound represented by the structural formula (I) of the present invention is used as the negative electrode film-forming additive, the negative electrode of the battery is preferably graphite, silicon carbon or metallic lithium.

When the compound represented by the structural formula (I) of the present invention is used as a negative electrode film-forming additive, the negative electrode film-forming additive may further include other negative electrode film-forming additives.

As a preferred way, the negative electrode film-forming additive comprises a compound represented by structural formula (I) and is selected from vinylene carbonate, 1,3-propane sultone, tris(trimethylsilane)borate , at least one of fluoroethylene carbonate and ethylene ethylene carbonate.

As a further preferred manner, the negative electrode film-forming additive comprises a compound represented by structural formula (I) and is selected from vinylene carbonate, 1,3-propane sultone and tris(trimethylsilane)borate at least one of.

The present invention also provides an electrolyte for a lithium ion battery, which contains the compound represented by the above-mentioned structural formula (I).

When the lithium ion battery electrolyte of the present invention contains the compound represented by the structural formula (I), the content of the compound represented by the structural formula (I) in the lithium ion battery electrolyte is preferably 0.1% to 5%. More preferably, in the lithium ion battery electrolyte, the content of the compound represented by the structural formula (I) is 0.2% to 2%.

The lithium ion battery electrolyte provided by the present invention can further contain lithium salt, organic solvent and additives in addition to the compound represented by the above-mentioned structural formula (I), that is, the lithium ion battery electrolyte contains lithium salt, organic solvent , additives and compounds represented by structural formula (I).

The lithium ion battery electrolyte provided by the present invention can use the lithium salt commonly used in the art. Preferably, the lithium salt is selected from LiBF ₄ , LiPF ₆ , LiFSI, LiTFSI, LiAsF ₆ , LiClO ₄ , LiSO ₃ CF ₃ , LiC ₂ O ₄ BC ₂ O ₄ , LiF ₂ BC ₂ O ₄ , LiDTI, LiPO At least one of ₂ F ₂ .

The organic solvent used in the lithium ion battery electrolyte provided by the present invention can be an organic solvent commonly used in the art. Preferably, the organic solvent is selected from at least one of carbonate, phosphate, carboxylate, ether, nitrile and sulfone solvents.

In the lithium ion battery electrolyte provided by the present invention, the additive used may be an additive that helps to improve the performance of the electrolyte. Preferably, the additive is selected from at least one of negative electrode film-forming additives, water-removing additives, positive electrode film-forming additives, conductivity-enhancing additives, wettability-improving additives, and flame retardant additives. Further preferably, the additive is selected from biphenyl, vinylene carbonate (VC), fluoroethylene carbonate, ethylene ethylene carbonate, propylene sulfite, butylene sulfite, 1,3-propanesulfonic acid Acid lactone (PS), 1,4 butanesultone, 1,3-(1-propene)sultone, vinyl sulfite, vinyl sulfate, cyclohexylbenzene, tris(trimethylsilane)boron At least one of acid ester (TMSB), tris(trimethylsilane) phosphate, tert-butylbenzene, succinonitrile, ethylene glycol bis(propionitrile) ether and succinic anhydride. More preferably, the additive is selected from the group consisting of vinylene carbonate, 1,3-propane sultone, tris(trimethylsilane) borate, fluoroethylene carbonate and ethylene ethylene carbonate. at least one.

When the lithium ion battery electrolyte of the present invention contains lithium salt, organic solvent, additive and compound represented by structural formula (I), the lithium salt, organic solvent, additive and compound represented by structural formula (I) are in the electrolyte The content should be able to improve the performance of the battery. Preferably, in the lithium ion battery electrolyte, the content of lithium salt is 5-15%, the content of organic solvent is 72-95%, the content of additives is 0.2-10%, and the content of the compound represented by structural formula (I) is 0.1% to 5%.

The present invention also provides a lithium ion battery containing the above electrolyte. In addition to containing the above-mentioned electrolyte, the lithium ion battery of the present invention also contains other common components of the lithium ion battery described in the art.

The compound shown in the structural formula (I) provided by the present invention, when it is used for battery electrolyte, has the following advantages compared to the prior art:

(1) The compound represented by the structural formula (I) can effectively improve the interface wettability of the electrolyte to the electrode and reduce the interface contact resistance;

(2) The reduction potential of the compound represented by the structural formula (I) is high, and can be reduced and decomposed on the surface of negative electrodes such as graphite, silicon negative electrode and metal lithium prior to common solvents in the electrolyte to generate SEI film;

(3) The content of N and Li in the generated SEI film increases, which can not only make the SEI film more stable, but also can effectively reduce the resistance of the SEI film;

(4) It can effectively reduce the interface impedance and charge transfer impedance between anode materials such as graphite and silicon carbon and the electrolyte, thereby effectively improving the cycle stability and rate performance of these anode materials.

Description of drawings

FIG. 1 shows the LSV curves of the battery electrolytes prepared in Example 1 and Comparative Example 1. FIG.

FIG. 2 is a scanning electron microscope image of the surface of the graphite negative electrode of the graphite/metal lithium half-cell assembled in Example 1 and Comparative Example 1. FIG.

FIG. 3 is a graph showing the rate performance of the electrolyte solutions prepared in Example 1 and Comparative Example 1. FIG.

FIG. 4 is an XPS diagram of the surface of the graphite negative electrode after cycling of the batteries assembled with the electrolytes prepared in Example 1 and Comparative Example 1.

Detailed ways

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 realize that the present invention covers all alternatives, modifications and equivalents that may be included within the scope of the claims.

1. Electrolyte preparation and battery performance test

Example 1

(1) Preparation of electrolyte

Ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC=3:2:5, and then lithium hexafluorophosphate (LiPF ₆ ) was added until The molar concentration of lithium hexafluorophosphate in the electrolyte is 1 mol/L, and then 1% of compound 1 is added based on the total mass of the electrolyte. The structure of compound 1 is as follows:

(2) Preparation of positive plate

Mix positive electrode active material lithium nickel cobalt manganese oxide LiNi _0.5 Co _0.2 Mn _0.3 O ₂ or lithium cobalt oxide LiCoO ₂ , conductive carbon black Super-P and binder polyvinylidene fluoride ( PVDF), and then dispersed them in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry is uniformly coated on both sides of the aluminum foil, dried, calendered and vacuum-dried, and the aluminum lead wires are welded with an ultrasonic welder to obtain a positive electrode plate.

(3) Preparation of negative plate

Mix the negative active material artificial graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) in a mass ratio of 92:2:3:3, and then disperse them in the Ionized water to obtain a negative electrode slurry. Coating the slurry on both sides of the copper foil, drying, calendering and vacuum drying, and welding nickel lead wires with an ultrasonic welder to obtain a negative electrode plate.

(4) Preparation of cells

A polyethylene microporous film with a thickness of 20 μm was placed between the positive electrode plate and the negative electrode plate as a separator, and then the sandwich structure composed of the positive electrode plate, the negative electrode plate and the separator was wound, and the tabs were drawn out and then encapsulated in an aluminum plastic film. Cells to be injected.

(5) Liquid injection and formation of battery cells

In a glove box with a moisture content of less than 10 ppm, the electrolyte prepared above was injected into the cell, and the amount of electrolyte should ensure that the gap in the cell was filled. Then it is formed according to the following steps: 0.01C constant current charging for 30min, 0.02C constant current charging for 60min, 0.05C constant current charging for 90min, 0.1C constant current charging for 240min, then set aside for 1hr, shape and seal, and then further charge at 0.2C constant current It is charged to 4.40V with current, and after 24hrs at room temperature, it is discharged to 3.0V with a constant current of 0.2C.

(6) Rate performance test

Use a battery whose positive active material is lithium cobalt oxide LiCoO ₂ , charge it to 4.40V at a constant current of 0.5C, then charge it at a constant voltage until the current drops to 0.1C, and then discharge it to 3.0V at a constant current of 0.5C, and so on. 7 weeks. Then charge to 4.40V with constant current of 1.0C, 1.5C, 2.0C and 0.5C in turn, then charge with constant voltage until the current drops to 0.1C, and then discharge to 3.0V with corresponding current constant current, each rate current Next cycle for 7 weeks. The rate performance data obtained from the test are shown in Figure 2.

(7) Cycle performance test

Use a battery whose positive active material is lithium nickel cobalt manganese oxide LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , charge it with a constant current of 1C to 4.40V, then charge it with a constant voltage until the current drops to 0.1C, and then charge it with a constant current of 1C. Discharge to 3.0V for 300 cycles, record the discharge capacity of the first week and the discharge capacity of the 300th cycle, and calculate the capacity retention rate of the battery cycle as follows:

Capacity retention rate=(discharge capacity at 300th cycle/discharge capacity at 1st week)*100%.

The obtained normal temperature cycle performance data are shown in Table 1.

Example 2

The mass content of compound 1 in the electrolyte prepared in Example 1 was changed to 0.2%, and the rest were prepared according to the same operating conditions as in Example 1. Electrolyte, positive plate, negative plate, cell, and the cell were injected And chemical formation and battery cycle performance testing. The obtained normal temperature cycle performance data are shown in Table 1.

Example 3

The mass content of compound 1 in the electrolyte prepared in Example 1 was changed to 0.5%, and the rest were prepared according to the same operating conditions as in Example 1. And chemical formation and battery cycle performance testing. The obtained normal temperature cycle performance data are shown in Table 1.

Example 4

The mass content of compound 1 in the electrolyte prepared in Example 1 was changed to 2%, and the rest were prepared according to the same operating conditions as in Example 1 to prepare electrolyte, positive plates, negative plates, and cells, and perform liquid injection of the cells And chemical formation and battery cycle performance testing. The obtained normal temperature cycle performance data are shown in Table 1.

Example 5

The mass content of compound 1 in the electrolyte prepared in Example 1 was changed to 5%, and the rest were prepared according to the same operating conditions as in Example 1. And chemical formation and battery cycle performance testing. The obtained normal temperature cycle performance data are shown in Table 1.

Example 6

The compound 1 in the prepared electrolyte in Example 1 was changed to compound 2, and the mass content of compound 2 in the electrolyte was changed to 1%, and the rest were prepared according to the same operating conditions as in Example 1. Negative plates, battery cells, and the liquid injection and formation of the battery cells, as well as the battery cycle performance test. The structural formula of compound 2 is as follows:

The obtained normal temperature cycle performance data are shown in Table 1.

Example 7

The compound 1 in the prepared electrolyte in Example 1 was changed to compound 2, and the mass content of compound 2 in the electrolyte was changed to 0.5%, and the rest were prepared according to the same operating conditions as in Example 1. Electrolyte, positive plate, Negative plates, battery cells, and the liquid injection and formation of the battery cells, as well as the battery cycle performance test. The obtained normal temperature cycle performance data are shown in Table 1.

Example 8

The compound 1 in the prepared electrolyte in Example 1 was changed to compound 2, and the mass content of compound 2 in the electrolyte was changed to 2%, and the rest were prepared according to the same operating conditions as in Example 1. Electrolyte, positive plate, Negative plates, battery cells, and the liquid injection and formation of the battery cells, as well as the battery cycle performance test. The obtained normal temperature cycle performance data are shown in Table 1.

Example 9

The compound 1 in the prepared electrolyte in Example 1 was changed to compound 3, and the mass content of compound 3 in the electrolyte was changed to 1%, and the rest were prepared according to the same operating conditions as in Example 1. Negative plates, battery cells, and the liquid injection and formation of the battery cells, as well as the battery cycle performance test. The structural formula of compound 3 is as follows:

The obtained normal temperature cycle performance data are shown in Table 1.

Example 10

The compound 1 in the prepared electrolyte in Example 1 was changed to compound 4, and the mass content of compound 4 in the electrolyte was changed to 1%, and the rest were prepared according to the same operating conditions as in Example 1. Electrolyte, positive plate, Negative plates, battery cells, and the liquid injection and formation of the battery cells, as well as the battery cycle performance test. The structural formula of compound 4 is as follows:

The obtained normal temperature cycle performance data are shown in Table 1.

Example 11

The compound 1 in the electrolyte prepared in Example 1 was changed to compound 5, and the mass content of compound 5 in the electrolyte was changed to 1%, and the rest were prepared according to the same operating conditions as in Example 1. Electrolyte, positive plate, Negative plates, battery cells, and the liquid injection and formation of the battery cells, as well as the battery cycle performance test. The structural formula of compound 5 is as follows:

The obtained normal temperature cycle performance data are shown in Table 1.

Example 12

The compound 1 in the electrolyte prepared in Example 1 is changed to the composition of compound 1 and TMSB (tris(trimethylsilane) borate), wherein in the electrolyte: the mass content of compound 1 is 1%, and the content of TMSB is 1%. The mass content is 1%. The rest were prepared according to the same operating conditions as in Example 1 to prepare the electrolyte, positive plate, negative plate, and cell, and carry out the liquid injection and formation of the cell and the cycle performance test of the battery. The obtained normal temperature cycle performance data are shown in Table 1.

Example 13

The compound 1 in the electrolyte prepared in Example 1 is changed to the composition of compound 1 and TMSB (tris(trimethylsilane) borate), wherein in the electrolyte: the mass content of compound 1 is 1%, and the content of TMSB is 1%. The mass content is 0.5%. The rest were prepared according to the same operating conditions as in Example 1 to prepare the electrolyte, positive plate, negative plate, and cell, and carry out the liquid injection and formation of the cell and the cycle performance test of the battery. The obtained normal temperature cycle performance data are shown in Table 1.

Example 14

The graphite in the preparation of the negative plate in Example 1 was replaced with a silicon carbon negative electrode (capacity was 450mAh/g), and the rest were prepared according to the same operating conditions as in Example 1. Electrolyte, positive plate, negative plate, and cell were carried out. The injection and formation of the liquid and the cycle performance test of the battery. The obtained normal temperature cycle performance data are shown in Table 1.

Example 15

The graphite in the preparation of the negative plate in Example 1 was replaced with a metal lithium negative electrode, and the rest were prepared according to the same operating conditions as in Example 1. cycle performance test. The obtained normal temperature cycle performance data are shown in Table 1.

Example 16

The LiNi _0.5 Co _0.2 Mn _0.3 O ₂ in the preparation of the positive plate in Example 1 was replaced with LiCoO ₂ , and the rest were prepared according to the same operating conditions as in Example 1. Electrolyte, positive plate, negative plate, and cell were prepared. Liquid injection and chemical formation and battery cycle performance testing. The obtained normal temperature cycle performance data are shown in Table 1.

Comparative Example 1

The compound 1 in the preparation of the electrolyte solution of Example 1 was removed, and the rest were prepared according to the same operating conditions as in Example 1 to prepare the electrolyte solution, positive plate, negative plate, and cell, and carry out the liquid injection and formation of the cell and the cycle performance of the battery. test. The obtained normal temperature cycle performance data are shown in Table 1.

Comparative Example 2

Compound 1 in the preparation of the electrolyte solution of Example 1 was changed to VC, and its mass content in the electrolyte solution was 1%, and the rest were prepared according to the same operating conditions as in Example 1. Cells, and perform cell injection and chemical formation and battery cycle performance tests. The obtained normal temperature cycle performance data are shown in Table 1.

Comparative Example 3

Compound 1 in the preparation of the electrolyte solution of Example 1 was changed to PS, and its mass content in the electrolyte solution was 1%, and the rest were prepared according to the same operating conditions as in Example 1. Cells, and perform cell injection and chemical formation and battery cycle performance tests. The obtained normal temperature cycle performance data are shown in Table 1.

Comparative Example 4

Compound 1 in the preparation of the electrolyte of Example 1 was changed to VC and PS, and the mass contents of VC and PS in the electrolyte were respectively 0.5%, and the rest were prepared according to the same operating conditions as in Example 1. Electrolyte, positive plate , negative plate, battery cell, and carry out the liquid injection and chemical formation of the battery cell and the cycle performance test of the battery. The obtained normal temperature cycle performance data are shown in Table 1.

Comparative Example 5

Compound 1 in the preparation of the electrolyte in Example 1 was changed to VC and PS, and the mass contents of VC and PS in the electrolyte were respectively 1%, and the rest were prepared according to the same operating conditions as in Example 1. Electrolyte, positive plate , negative plate, battery cell, and carry out the liquid injection and chemical formation of the battery cell and the cycle performance test of the battery. The obtained normal temperature cycle performance data are shown in Table 1.

Comparative Example 6

The compound 1 in the preparation of the electrolyte in Example 1 was removed, and the graphite in the preparation of the negative plate was replaced with a silicon carbon negative electrode (capacity was 450mAh/g), and the rest were prepared according to the same operating conditions as in Example 1. Electrolyte, positive plate , negative plate, battery cell, and carry out the liquid injection and chemical formation of the battery cell and the cycle performance test of the battery. The obtained normal temperature cycle performance data are shown in Table 1.

Comparative Example 7

The compound 1 in the preparation of the electrolyte in Example 1 was removed, and the graphite in the preparation of the negative plate was replaced with a metal lithium negative electrode, and the rest were prepared according to the same operating conditions as in Example 1. And carry out the liquid injection and chemical formation of the battery cell and the cycle performance test of the battery. The obtained normal temperature cycle performance data are shown in Table 1.

Comparative Example 8

The compound 1 in the preparation of the electrolyte in Example 1 was removed, and the LiNi _0.5 Co _0.2 Mn _0.3 O ₂ in the preparation of the positive plate was replaced with LiCoO ₂ , and the rest were prepared according to the same operating conditions as in Example 1. Negative plates, battery cells, and the liquid injection and formation of the battery cells, as well as the battery cycle performance test. The obtained normal temperature cycle performance data are shown in Table 1.

Table 1

2. Performance test of additive anode film formation

In order to verify the negative electrode film-forming performance of the lithium ion battery electrolyte additive shown in formula (1) provided by the present invention, the present invention takes the electrolyte prepared in Example 1 and Comparative Example 1 as samples to carry out LSV curve, graphite negative electrode after cycling Surface SEM image, rate performance test of LiCoO ₂ /graphite battery and X-ray photoelectron spectroscopy test.

1. LSV curve test

The test method of the LSV curve is as follows:

The LSV curve test method is as follows: three-electrode method (graphite electrode is used as the working electrode, metal lithium is used as the counter electrode and reference electrode, respectively), the scanning rate is 0.05mV/s, and the scanning lower limit is 0.01V.

In order to verify the negative electrode film-forming ability of the compound represented by the structural formula (I), we tested the LSV curves of the three electrolytes in Example 1 and Comparative Example 1, respectively.

It can be seen from Figure 1 that the electrolyte prepared in Comparative Example 1 was reduced and decomposed from 0.65V, while the reduction potential of the electrolyte prepared in Example 1 was raised from 0.65V to 1.45V, and the reduction peak at 0.65V disappeared, This indicates that the reduction reaction of compound 1 takes place in preference to EC, and the reduction product is deposited on the surface of the graphite anode to assist in the formation of a more stable SEI film, which can effectively suppress the side reaction between the electrolyte and the electrode in the subsequent cycling process, thereby significantly improving the battery rate performance. and cycle stability.

2. Scanning electron microscope test

In order to further confirm the influence of compound 1 on the reduction and film formation on the surface of the graphite negative electrode, the initial electrode plate of the graphite negative electrode, the electrode plate after circulating in the electrolyte of Comparative Example 1 for 3 weeks, and the electrode plate after circulating in the electrolyte of Example 1 for 3 weeks were taken respectively. Scanning electron microscopy tests were performed. The results are shown in Figure 2, the graphite particles on the surface of the electrode sheet circulating in the electrolyte of Example 1 containing the additive described in formula (1) are clearer and the surface is smoother, and it can be seen from the enlarged view (i) that more Dense and uniform SEI film. In Comparative Example 1, the graphite particles on the surface of the electrode circulating in the electrolyte were covered with thick deposits, because the SEI film on the surface was unstable and not dense, and the electrolyte continued to undergo a reduction reaction on the surface of the graphite negative electrode.

3. Rate performance test

The rate performance was tested in LiCoO ₂ /graphite cells, which were charged and discharged at rate currents of 0.5C, 1.0C, 1.5C, and 2.0C, respectively. The results are shown in FIG. 3 , the rate performance of the battery of Example 1 containing the additive of formula (1) is significantly better than that of Comparative Example 1. The improvement in rate performance can be attributed to two aspects: one is the preferential film formation of the additive described in formula (1), which forms an interface film with good electrical conductivity on the surface of the graphite anode, and the components containing CF and C-Si bonds are improved. The stability of the interface film is improved; the second is the addition of the additive described in formula (1), which improves the liquid wettability and permeability of the electrolyte.

4. X-ray photoelectron spectroscopy test

Using the electrolytes in Comparative Example 1 and Example 1 to assemble metal lithium/graphite half-cells, take the graphite negative pole piece after the cycle, and carry out X-ray photoelectron spectroscopy analysis. The results are shown in Figure 4. Example 1 The C-C and C-O components on the graphite surface decreased, and the LiF component increased significantly, indicating that the additive formed an SEI film on the graphite surface, and the SEI film had a higher proportion of LiF components, thereby improving the surface stability of the interface film.

From the above examples and comparative examples, it can be seen that the additive of formula (1) provided by the present invention can not only undergo reductive decomposition in preference to the solvent, but also the decomposition products are deposited on the surface of graphite, silicon carbon and metal lithium, forming relatively stable and high conductivity. The SEI film can also improve the electrolyte wettability, thereby effectively improving the rate performance and cycle performance of the battery.

Claims (21)

1. A battery electrolyte additive shown in a structural formula (I),

wherein:

r1, R2, R3, R4 and R5 are independently selected from C1-C20 alkyl, C2-C20 alkenyl, C1-C20 alkoxy, C1-C20 haloalkyl, C2-C20 haloalkenyl and C1-C20 haloalkoxy.

2. The battery electrolyte additive of claim 1 wherein in said structural formula (I):

r1, R2, R3, R4 and R5 are independently selected from C1-C12 alkyl, C2-C12 alkenyl, C1-C12 alkoxy, C1-C12 haloalkyl, C2-C12 haloalkenyl and C1-C12 haloalkoxy.

3. The battery electrolyte additive of claim 2 wherein in said structural formula (I):

r1, R2, R3, R4 and R5 are independently selected from C1-C5 alkyl, C2-C5 alkenyl, C1-C5 alkoxy, C1-C5 haloalkyl, C2-C5 haloalkenyl and C1-C5 haloalkoxy.

4. A battery electrolyte additive according to claim 3 wherein in said structural formula (I):

r1, R2, R3, R4 and R5 are independently selected from C1-C5 alkyl and C1-C5 haloalkyl.

5. The battery electrolyte additive of claim 4 wherein in said structural formula (I):

r1, R2, R3, R4 and R5 are independently selected from C1-C3 alkyl and C1-C3 haloalkyl.

6. The battery electrolyte additive of claim 1 wherein said additive is used as a negative electrode film forming additive.

7. The battery electrolyte additive of claim 6 wherein said additive is used as a negative electrode film forming additive, said battery negative electrode being selected from the group consisting of graphite, silicon carbon, and metallic lithium.

8. The battery electrolyte additive of claim 6 wherein the negative film forming additive comprises a compound of formula (I) and at least one member selected from the group consisting of vinylene carbonate, 1, 3-propanesultone, tris (trimethylsilane) borate, fluoroethylene carbonate and vinylethylene carbonate.

9. The battery electrolyte additive of claim 8 wherein the negative film forming additive comprises a compound of formula (I) and at least one member selected from the group consisting of vinylene carbonate, 1, 3-propane sultone, and tris (trimethylsilane) borate.

10. A lithium ion battery electrolyte, characterized in that it contains a compound of formula (I) according to claim 1.

11. The lithium ion battery electrolyte of claim 10, wherein the content of the compound represented by the structural formula (I) in the lithium ion battery electrolyte is 0.05% to 5%.

12. The lithium ion battery electrolyte of claim 11, wherein the content of the compound represented by the structural formula (I) in the lithium ion battery electrolyte is 0.5% to 5%.

13. The lithium ion battery electrolyte of claim 12, wherein the content of the compound represented by the structural formula (I) in the lithium ion battery electrolyte is 1% to 2%.

14. The lithium ion battery electrolyte of claim 10, wherein the lithium ion battery electrolyte comprises a lithium salt, an organic solvent, an additive, and a compound of formula (I).

15. The lithium ion battery electrolyte of claim 14, wherein the lithium salt is selected from the group consisting of LiBF₄、LiPF₆、LiFSI、LiTFSI、LiAsF₆、LiClO₄、LiSO₃CF₃、LiC₂O₄BC₂O₄、LiF₂BC₂O₄、LiDTI、LiPO₂F₂At least one of (1).

16. The lithium ion battery electrolyte of claim 14, wherein the organic solvent is selected from at least one of carbonate, phosphate, carboxylate, ether, nitrile, and sulfone solvents.

17. The lithium ion battery electrolyte of claim 14, wherein the additive is selected from at least one of a negative electrode film forming additive, a water removal additive, a positive electrode film forming additive, a conductivity enhancing additive, a wettability enhancing additive, and a flame retardant additive.

18. The lithium ion battery electrolyte of claim 14 wherein the additive is selected from at least one of biphenyl, vinylene carbonate, fluoroethylene carbonate, vinylethylene carbonate, propylene sulfite, butylene sulfite, 1, 3-propane sultone, 1,4 butane sultone, 1,3- (1-propene) sultone, vinyl sulfite, vinyl sulfate, cyclohexylbenzene, tris (trimethylsilane) borate, tris (trimethylsilane) phosphate, t-butyl benzene, succinonitrile, ethylene glycol bis (propionitrile) ether, and succinic anhydride.

19. The lithium ion battery electrolyte of claim 18 wherein the additive is selected from at least one of vinylene carbonate, 1, 3-propane sultone, tris (trimethylsilane) borate, fluoroethylene carbonate, and vinyl ethylene carbonate.

20. The lithium ion battery electrolyte of claim 14, wherein the lithium ion battery electrolyte contains 5 to 15% of lithium salt, 72 to 95% of organic solvent, 0.2 to 10% of additive, and 0.1 to 5% of compound represented by structural formula (I).

21. A lithium ion battery, characterized in that it contains the battery electrolyte according to claim 10.

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