CN118040044B - Electrolyte and lithium ion battery - Google Patents

Abstract

The present invention provides an electrolyte additive, an electrolyte and a lithium ion battery, and relates to the technical field of lithium ion batteries. The electrolyte additive provided by the present invention is a five-membered ring structure having N and S heteroatoms. When the electrolyte additive is added to the electrolyte of the lithium ion battery, the additive can be ring-opened and polymerized in the preferential oxidation/reduction process on the surface of the positive/negative electrode to form a polymer that can stabilize the positive/negative electrode structure and has high ionic conductivity and high electrochemical stability, so as to effectively inhibit the dissolution and migration of metal ions and active oxygen ions in the positive electrode, and inhibit the direct contact between the highly active positive/negative electrode and the electrolyte, so as to achieve the purpose of improving the stability of the positive/negative electrode structure and inhibiting the interface side reaction, and improving the electrochemical performance of the battery.

Description

Electrolyte and lithium ion battery

Technical Field

The present invention relates to the technical field of lithium ion batteries, and in particular to an electrolyte additive, an electrolyte, a preparation method and a lithium ion battery.

Background Art

Lithium-ion batteries are widely used in portable electronic devices, electric vehicles and other fields due to their high energy density, high working potential and environmental friendliness, and have shown great application potential in electric aircraft, military and other fields. However, as electronic products continue to develop towards intelligence, thinness and ultra-long standby, and large equipment such as electric vehicles and electric aircraft continue to have increasing requirements for long battery life and long service life, higher requirements are placed on the cycle stability, energy density and safety of batteries.

However, the cycle stability, energy density and safety of lithium-ion batteries are mainly determined by the interfacial stability between the electrolyte and the electrode. On the one hand, the commonly used positive electrodes are mostly made of metal oxide materials. In the deep delithiation state, the oxidized high-valent metal ions will catalyze the decomposition of the electrolyte, resulting in metal ion dissolution and structural collapse, and this process will be exacerbated by the increase of battery voltage and the participation of oxygen in the electrode in charge compensation. In addition, the dissolved metal ions and active oxygen will migrate to the negative electrode and be reduced on the surface of the negative electrode of the battery, thereby destroying the original solid electrolyte membrane (SEI) on the surface of the negative electrode, aggravating the interfacial side reactions on the negative electrode side, and even inducing thermal runaway risks such as combustion and explosion in severe cases. Therefore, improving the interfacial stability between the positive/negative electrode and the electrolyte is crucial to the overall improvement of battery performance.

Summary of the invention

The object of the present invention is to provide an electrolyte additive, an electrolyte, a preparation method and a lithium ion battery. By providing an additive that introduces N and S elements into the main framework of the molecular structure, an interface film with high ionic conductivity and high electrochemical stability can be formed on the surface of the positive and negative electrodes, thereby improving the interface stability between the positive/negative electrodes and the electrolyte, and enhancing the long cycle performance, energy density and safety performance of the lithium ion battery.

In the first aspect, the present invention provides an electrolyte additive, the structure of which is shown in Formula I:

,

Wherein, ^R1 and ^R2 are independently substituted or unsubstituted alkyl or aryl.

In a second aspect, the present invention further provides an electrolyte comprising the electrolyte additive provided above.

Optionally, the electrolyte further includes an organic solvent and a lithium salt dissolved in the organic solvent.

Optionally, the concentration of the electrolyte additive in the electrolyte is 0.1-10wt.%.

Optionally, the concentration of the lithium salt in the electrolyte is 0.2-5 mol/L

Optionally, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonate)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, lithium bis(oxalatoborate) and lithium perchlorate.

Optionally, the organic solvent includes at least one of a carbonate non-aqueous organic solvent, an ether non-aqueous organic solvent, a sulfone non-aqueous organic solvent, a nitrile non-aqueous organic solvent and a carboxylate non-aqueous organic solvent;

The carbonate-based non-aqueous organic solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, fluoroethylene carbonate, fluoroethyl methyl carbonate, fluoropropylene carbonate, difluoroethylene carbonate, methyl trifluoroethyl carbonate, and tris(trifluoroethyl) carbonate;

The ether non-aqueous organic solvent includes at least one of ethylene glycol dimethyl ether, pentyl oxide, methyl perfluorobutyl ether, ethyl perfluorobutyl ether and fluoroethyl propyl ether;

The sulfone non-aqueous organic solvent includes at least one of sulfolane, dimethyl sulfoxide, n-butyl sulfone, dimethyl sulfone, phenyl sulfone and methyl ethyl sulfone;

The nitrile non-aqueous organic solvent comprises at least one of acetonitrile, succinonitrile, adiponitrile, suberonitrile and hexanetrinitrile;

The carboxylate non-aqueous solvent includes at least one of ethyl acetate, methyl acetate, ethyl formate, ethyl difluoroacetate, methyl 2,3,3,3-tetrafluoropropionate and methyl 2,2-difluoro-2(fluorosulfonyl)acetate.

Optionally, the electrolyte further comprises a functional additive, and the concentration of the functional additive in the electrolyte is 0.1-10 wt.%.

Optionally, the functional additive includes at least one of vinyl ethylene carbonate, vinylene carbonate, propylene sulfite, dimethyl sulfite, vinyl sulfate, methylene methanedisulfonate, n-propyl phosphoric anhydride, triallyl phosphate, succinic anhydride and methylsulfonic anhydride.

In a third aspect, the present invention also provides a lithium-ion battery comprising any of the above-mentioned optional electrolytes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a graph showing the cycle performance of lithium ion batteries prepared in Example 8 of the present invention and Comparative Example 1;

FIG2 is a graph showing the cycle performance of lithium ion batteries prepared in Example 8 of the present invention and Comparative Example 1;

FIG3 is a graph showing the cycle performance of lithium ion batteries prepared in Examples 10-11 of the present invention and Comparative Examples 1-2;

FIG4 is a graph showing the cycle performance of the lithium ion batteries prepared in Example 12 of the present invention and Comparative Example 1.

DETAILED DESCRIPTION

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be understood by people with general skills in the field to which the present invention belongs. "Including" and similar words used in this article mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

An embodiment of the present invention provides an electrolyte additive, the structural formula of which is shown in Formula I.

.

Wherein, ^R1 and ^R2 groups are independently any one of substituted alkyl, substituted aryl, unsubstituted alkyl and unsubstituted aryl.

In some embodiments, the unsubstituted alkyl group may be any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclopropyl and cyclobutyl.

In some embodiments, the substituted alkyl group may be any one of alkenylalkyl, alkynylalkyl and haloalkyl. In fact, alkenylalkyl may be any one of allyl, butylene, isobutylene, pentylene and isopentylene, alkynylalkyl may be any one of propargyl, butylene, isobutylene, pentylene and isopentylene, haloalkyl may be any one of trifluoromethyl, trifluoroethyl, trifluoropropyl, pentafluoropropyl, trifluorobutyl and pentafluorobutyl.

In some embodiments, the substituted aryl group may be any one of p-trifluoromethylphenyl, p-fluorophenyl, p-chlorophenyl, o-trifluoromethylphenyl, and p-fluorobenzyl.

The electrolyte additive provided by the present invention is a five-membered ring structure doped with N and S heteroatoms at the same time. When the electrolyte additive is added to the electrolyte of the lithium ion battery, the additive can be ring-opened and polymerized in the preferential oxidation/reduction process on the surface of the positive/negative electrode to form a polymer that can stabilize the positive/negative electrode structure and has high ionic conductivity and high electrochemical stability, so as to effectively inhibit the dissolution and migration of metal ions and active oxygen ions in the positive electrode, and inhibit the direct contact between the highly active positive/negative electrode and the electrolyte, so as to achieve the purpose of improving the stability of the positive/negative electrode structure and inhibiting the interface side reaction, and improving the electrochemical performance of the battery.

In addition, the present invention also provides an electrolyte, which includes the electrolyte additive provided by any of the above embodiments.

In some embodiments, the concentration of the electrolyte additive in the electrolyte is 0.1-10%. Within this concentration range, the additive can achieve better performance. When the content of the additive is lower than 0.1 wt.%, it is difficult to form a uniform protective film on the positive/negative electrode surface due to its too low content, isolating the direct contact between the highly reactive electrode and the electrolyte; similarly, when the content of the additive is higher than 10 wt.%, the interface layer formed by the in-situ decomposition of the additive on the positive/negative surface will be relatively thick, hindering the transmission of ions and electrons and reducing the battery capacity.

In some embodiments, the electrolyte further includes an organic solvent and a lithium salt dissolved in the organic solvent. In fact, the electrolyte additive is also dissolved in the organic solvent to form a stable solution.

In some embodiments, the organic solvent is a non-aqueous organic solvent commonly used in the art for preparing electrolytes. Specifically, the organic solvent may be at least one of carbonate, ether, sulfone, nitrile and carboxylate organic solvents.

More specifically, when the organic solvent is a carbonate organic solvent, it can be at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, fluoroethylene carbonate, fluoroethyl methyl carbonate, fluoropropylene carbonate, bisfluoroethylene carbonate, methyl trifluoroethyl carbonate, and tris(trifluoroethyl) carbonate.

More specifically, when the organic solvent is an ether organic solvent, it may be at least one of ethylene glycol dimethyl ether, pentyl oxide, methyl perfluorobutyl ether, ethyl perfluorobutyl ether and fluoroethyl propyl ether.

More specifically, when the organic solvent is a sulfone organic solvent, it may be at least one of sulfolane, dimethyl sulfoxide, n-butyl sulfone, dimethyl sulfone, phenyl sulfone and methyl ethyl sulfone.

More specifically, when the organic solvent is a nitrile organic solvent, it may be at least one of acetonitrile, succinonitrile, adiponitrile, suberonitrile and hexanetrinitrile.

More specifically, when the organic solvent is a carboxylate organic solvent, it may be at least one of ethyl acetate, methyl acetate, ethyl formate, ethyl difluoroacetate, methyl 2,3,3,3-tetrafluoropropionate and methyl 2,2-difluoro-2(fluorosulfonyl)acetate.

In some embodiments, the lithium salt dissolved in the organic solvent includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonate)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, lithium bisoxalatoborate and lithium perchlorate.

In some embodiments, the concentration of lithium salt in the electrolyte is 0.2-5 mol/L.

In some embodiments, the electrolyte further includes a functional additive, specifically, the functional additive includes at least one of vinyl ethylene carbonate, vinyl carbonate, propylene sulfite, dimethyl sulfite, vinyl sulfate, methylene methane disulfonate, n-propyl phosphoric anhydride, triallyl phosphate, succinic anhydride and methylsulfonic anhydride.

In some embodiments, the concentration of the functional additive in the electrolyte is 0.1-10 wt.%.

An embodiment of the present invention further provides a lithium-ion battery, comprising the electrolyte in any of the above embodiments.

In some embodiments, in lithium-ion batteries, layered oxide positive electrodes represented by LiCoO ₂ , ternary LiNi _x Co _y Mn _1-xy O ₂ (x, y>0, and x+y<1) or LiNi _x Co _y Al _1-xy O ₂ (x, y>0, and x+y<1), lithium-rich xLi ₂ MnO ₃ · (1-x) LiMO ₂ (M=Ni, Co, Mn, 0<x<1), etc., polyanion positive electrodes represented by LiFePO ₄ , LiMn _1-x Fe _x PO ₄ (x<1), LiCoPO ₄ , etc., and polyanion positive electrodes represented by LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O 4 , etc. are used. ₄ , etc.; and at least one of the negative electrode materials such as lithium metal, graphite, silicon carbon, micro/nano silicon, etc., while other positive/negative electrode materials for batteries that may involve interfacial side reactions are not excluded, such as Na _x MO ₂ (M is a transition metal atom, 0＜x≤1) positive electrode in sodium ion batteries, Na ₃ V ₂ (PO ₄ ) ₃ positive electrode, and soft/hard carbon negative electrode.

Example 1

Embodiment 1 of the present invention provides a method for preparing an electrolyte additive, comprising the following steps:

95.0397 mg (0.5 mmol) of 1-(4-fluorophenyl)-4-methyl-1-yn-3-one was used as raw material one, 95.9651 mg (0.6 mmol) of potassium ethyl xanthate was used as raw material two, and 289.8858 mg (2.0 mmol) of ammonium iodide, 9.0 mg (0.5 mmol) of deionized water and 2.0 mL of N , N -dimethylformamide were reacted under air atmosphere for 12 hours, and then 81.4097 mg of electrolyte additive (abbreviated as NS-1) was obtained by column chromatography separation and purification, and the calculated yield was 75%.

Specifically, the structural formula of the electrolyte additive NS-1 provided in this embodiment 1 is as follows:

.

Embodiment 2-7

Embodiment 2-7 of the present invention provides a method for preparing an electrolyte additive, which is different from Embodiment 1 in that (raw materials and product structures) are shown in Table 1 below.

Table 1

,

Example 8

Embodiment 8 of the present invention provides a method for preparing a lithium ion battery, adding the electrolyte additive NS-1 prepared in Embodiment 1, comprising the following steps:

S1. Prepare electrolyte: In a glove box filled with argon, stir and mix ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7, and then add lithium hexafluorophosphate and additive NS-1 to the mixed solution in sequence; wherein the amount of lithium hexafluorophosphate added is such that the concentration of lithium hexafluorophosphate in the electrolyte is 1.2 mol/L, and the amount of additive NS-1 added is such that the content of additive NS-1 in the electrolyte is 1 wt.%;

S2. Assemble the battery: Use the ternary material LiNi _0.9 Co _0.5 Mn _0.5 O ₂ as the positive electrode material, use metallic lithium as the negative electrode material, and drip the electrolyte containing the NS-1 additive on both sides of the PP-based separator respectively, and then package to obtain a lithium-ion battery.

Example 9

A method for preparing a lithium-ion battery provided in Example 9 of the present invention is different from that in Example 8 in that the electrolyte additive NS-2 prepared as in Example 2 is added, and in step S1 of preparing the electrolyte, lithium hexafluorophosphate and the additive NS-2 are sequentially added to the mixed solution, and the amount of the additive NS-2 added is such that the content of the additive NS-2 in the electrolyte is 10wt.%.

Example 10

A method for preparing a lithium-ion battery provided in Example 10 of the present invention is different from that in Example 8 in that the electrolyte additive NS-5 prepared as in Example 5 is added, and in step S1 of preparing the electrolyte, lithium hexafluorophosphate and the additive NS-5 are sequentially added to the mixed solution, and the amount of the additive NS-2 added is such that the content of the additive NS-2 in the electrolyte is 0.5 wt.%.

Embodiment 11

A method for preparing a lithium-ion battery provided in Example 11 of the present invention is different from that in Example 8 in that the electrolyte additive NS-5 and other functional additives such as vinylene carbonate prepared in Example 5 are added, and in step S1 of preparing the electrolyte, lithium hexafluorophosphate, additive NS-5 and functional additive vinylene carbonate are added to the mixed solution in sequence, and the amounts of additive NS-2 and vinylene carbonate added are such that the contents of additive NS-2 and vinylene carbonate in the electrolyte are both 0.5 wt.%.

Example 12

A method for preparing a lithium-ion battery provided in Example 12 of the present invention is different from that in Example 8 in that the electrolyte additive NS-7 prepared as in Example 7 is added, and in step S1 of preparing the electrolyte, lithium hexafluorophosphate and the additive NS-7 are sequentially added to the mixed solution, and the amount of additive NS-2 added is such that the content of the additive NS-7 in the electrolyte is 0.1 wt.%.

Comparative Example 1

Comparative Example 1 of the present invention provides a method for preparing a lithium ion battery, which is different from Example 8 in that the electrolyte additive NS-1 prepared as in Example 1 is not added, and in step S1 of preparing the electrolyte, only lithium hexafluorophosphate is added to the mixed solution.

Comparative Example 2

Comparative Example 1 of the present invention provides a method for preparing a lithium ion battery, which is different from Example 8 in that the electrolyte additive NS-1 prepared as in Example 1 is not added, and in step S1 of preparing the electrolyte, only lithium hexafluorophosphate and the functional additive ethylene carbonate are added to the mixed solution.

Performance Testing

The lithium ion batteries prepared in Examples 8-12 and Comparative Examples 1-2 were subjected to electrochemical performance tests at a rate of 1C (1C=200mAh/g) and room temperature, with a voltage range of 3.0-4.3V. The test results are shown in Figures 1-4.

Performance Analysis

As can be seen from Figure 1, the addition of NS-1 in Example 8 can significantly improve the discharge capacity of the lithium-ion battery and the capacity retention rate after cycling, from 71% in Comparative Example 1 to 89% in Example 8. This is mainly due to the interface film with high ionic conductivity and electrochemical stability formed by NS-1 on the surface of the positive/negative materials, which can well protect the electrodes and inhibit the decomposition of the electrolyte, thereby improving the service life of the lithium-ion battery.

As can be seen from Figure 2, when the addition amount of NS-2 in Example 9 reaches 10wt.%, due to the increase in the content of the electrolyte additive, the interface layer formed by the additive on the positive/negative electrode surface is thicker, which will reduce the battery capacity. However, during the long cycle process, the capacity retention rate of the lithium-ion battery in Example 9 (78%) is still higher than that in Comparative Example 1 (71%), which is beneficial to promoting the stability of the battery's cycle performance.

As can be seen from Figure 3, the functional additive ethylene carbonate was not added in Comparative Example 1 and Example 10, while the functional additive ethylene carbonate was added in Comparative Example 2 and Example 11. By comparison, it was found that the electrochemical performance of the batteries of Example 10 and Example 11 containing the NS-5 additive was better than that of Comparative Example 1 and Comparative Example 2.

As can be seen from Figure 4, even when the addition amount of the electrolyte additive NS-7 in Example 12 is only 0.1%, the attenuation rate of the battery under long cycle is still less than that of Comparative Example 1, which indicates that 0.1wt% of the electrolyte additive can also improve the cycle performance stability and service life of the lithium-ion battery.

Although the embodiments of the present invention are described in detail above, it is obvious to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as described in the claims. Moreover, the present invention described herein may have other embodiments and may be implemented or realized in a variety of ways.

Claims (9)

1. An electrolyte, characterized in that it comprises an electrolyte additive, wherein the structure of the additive is as shown in Formula I: , Wherein, ^R1 and ^R2 are independently substituted or unsubstituted alkyl or aryl; The unsubstituted alkyl group may be any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclopropyl and cyclobutyl; the substituted alkyl group may be any one of alkenylalkyl, alkynylalkyl and haloalkyl; the substituted aryl group may be any one of p-methylphenyl, p-methoxyphenyl, p-trifluoromethylphenyl, p-fluorophenyl, p-chlorophenyl, o-trifluoromethylphenyl and p-fluorobenzyl. 2. The electrolyte according to claim 1 is characterized in that it also includes an organic solvent and a lithium salt dissolved in the organic solvent. 3. The electrolyte according to claim 1 or 2, characterized in that the concentration of the electrolyte additive in the electrolyte is 0.1-10wt.%. 4. The electrolyte according to claim 2, characterized in that the concentration of the lithium salt in the electrolyte is 0.2-5 mol/L. 5. The electrolyte according to claim 2, characterized in that the lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonate)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, lithium bis(oxalatoborate) and lithium perchlorate. 6. The electrolyte according to claim 2, characterized in that the organic solvent comprises at least one of a carbonate non-aqueous organic solvent, an ether non-aqueous organic solvent, a sulfone non-aqueous organic solvent, a nitrile non-aqueous organic solvent and a carboxylate non-aqueous organic solvent; The carbonate non-aqueous organic solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, fluoroethylene carbonate, fluoroethyl methyl carbonate, fluoropropylene carbonate, difluoroethylene carbonate, methyl trifluoroethyl carbonate, and tris (trifluoroethyl) carbonate; The ether non-aqueous organic solvent includes at least one of ethylene glycol dimethyl ether, pentyl oxide, methyl perfluorobutyl ether, ethyl perfluorobutyl ether and fluoroethyl propyl ether; The sulfone non-aqueous organic solvent includes at least one of sulfolane, dimethyl sulfoxide, n-butyl sulfone, dimethyl sulfone, phenyl sulfone and methyl ethyl sulfone; The nitrile non-aqueous organic solvent comprises at least one of acetonitrile, succinonitrile, adiponitrile, suberonitrile and hexanetrinitrile; The carboxylate non-aqueous solvent includes at least one of ethyl acetate, methyl acetate, ethyl formate, ethyl difluoroacetate, methyl 2,3,3,3-tetrafluoropropionate and methyl 2,2-difluoro-2(fluorosulfonyl)acetate. 7. The electrolyte according to claim 2, characterized in that it also includes functional additives, and the concentration of the functional additives in the electrolyte is 0.1-10wt.%. 8. The electrolyte according to claim 7 is characterized in that the functional additive includes at least one of vinyl ethylene carbonate, vinylene carbonate, propylene sulfite, dimethyl sulfite, vinyl sulfate, methylene methanedisulfonate, n-propyl phosphoric anhydride, triallyl phosphate, succinic anhydride and methylsulfonic anhydride. 9. A lithium ion battery, characterized by comprising the electrolyte according to claims 1 to 8.