A lithium or sodium ion battery electrolyte additive and its application

Abstract

The invention discloses an electrolyte additive for a lithium or sodium ion battery and an application thereof, belonging to the technical field of lithium batteries; the electrolyte additive comprises g-C3N4 and a film-forming additive, and the g-C3N4 and the film-forming additive are coupled to form a negative electrode solid electrolyte interface film through intermolecular hydrogen bonding; the film-forming additive comprises one or more organic substances containing a carbonyl bond, an ether bond, a hydroxyl group, a carboxyl group, an amino group, a nitrile group, a thiol group, a sulfonic acid group, a hydrocarbon oxygen carbonyl group, a haloformyl group, a carbamoyl group, a formyl group, an amide group, and a halogen; in terms of mass fractions, the content of g-C3N4 accounts for 0.001%-5% of the total electrolyte mass, and the content of the film-forming additive accounts for 0.01%-30% of the total electrolyte mass. The present invention uses g-C3N4 with strong nucleophilic ability and a film-forming additive for coupling. During the electrochemical reaction, a negative electrode solid electrolyte interface film rich in nitrogen and with good conductivity is formed. The film can inhibit the generation of lithium / sodium dendrites, achieve uniform deposition of lithium / sodium, and improve the rate and cycle performance of the battery.

Description

Technical Field

[0001] The present invention relates to a lithium battery electrolyte additive, in particular to a lithium or sodium ion battery electrolyte additive and application thereof, belonging to the technical field of lithium batteries. Background Art

[0002] Lithium-ion batteries have received extensive attention in 3C, electric vehicles, hybrid power and large energy storage systems (ESSs) due to their high energy density, long life and low cost. However, the global lithium resources are limited, and the content of lithium in the earth's crust is only 0.0065%. With the development of new energy vehicles, the demand for batteries has increased significantly, and the bottleneck on the resource side has gradually emerged. The high cost has limited the large-scale application of lithium-ion batteries. Sodium reserves are very rich, with an abundance of 2.64% in the earth's crust, which is 440 times that of lithium resources. In addition, sodium resources are widely distributed and easy to refine. Sodium has emerged as a substitute for lithium and has received more and more attention in the battery field. Lithium and sodium belong to the alkali metal elements of Group IA of the periodic table. They have similar physical and chemical properties and can theoretically be used as metal ion carriers for secondary batteries.

[0003] In order to inhibit the growth of metal dendrites in secondary batteries and improve the safety and cycle life of batteries, researchers have proposed a large number of solutions, among which a uniform, dense and strong positive / negative electrode interface film (SEI film) is the basis for ensuring the long-term cycle performance of batteries. In order to form a stable, uniform and continuous SEI film on the surface of metallic sodium, Wang Weizhe et al. added Na-β-Al2O3 and g-C3N4 inorganic particles to a blend of polyethylene oxide and polycaprolactone to obtain a composite electrolyte with good ability to inhibit sodium dendrites. Existing patents also provide a variety of film-forming forms for forming positive electrode protective films and diaphragms in lithium batteries: for example, the electrolyte additive, lithium battery electrolyte and lithium battery with application publication number CN108649265A discloses an electrolyte additive that forms an SEI protective film on the positive electrode surface, which effectively inhibits the oxidative decomposition of organic solvents in the electrolyte and the damage to the structure of the positive electrode material during the circulation process; for example, the diaphragm functional coating material for improving the electrolyte retention and safety performance of lithium-ion batteries with application publication number CN112751140A discloses a diaphragm coating material that improves its heat resistance. However, the above-mentioned films are all formed on the positive electrode surface or between the positive and negative electrodes and the electrolyte, and there is no protective film formed on the negative electrode. During the charge and discharge cycle of lithium / sodium batteries, the problem of lithium / sodium dendrites will occur due to the poor conductivity of the SEI film.

[0004] Therefore, there is an urgent need for an SEI membrane that can be applied to both lithium and sodium ion batteries to inhibit the formation of lithium and sodium dendrites, thereby improving the safety and cycle life of the battery. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems in the prior art and provide a lithium or sodium ion battery electrolyte additive and its application. The electrolyte additive is prepared by coupling g-C3N4 and a film-forming additive. During the electrochemical reaction, a negative electrode solid electrolyte interface film rich in nitrogen and with good conductivity is formed. The film can inhibit the generation of lithium / sodium dendrites, achieve uniform deposition of lithium / sodium, and improve the cycle stability of the battery.

[0006] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a lithium or sodium ion battery electrolyte additive, the electrolyte additive includes g-C3N4 and a film-forming additive, the g-C3N4 and the film-forming additive are coupled to form a negative electrode solid electrolyte interface film through intermolecular hydrogen bonding; the film-forming additive includes one or more organic substances containing carbonyl bonds, ether bonds, hydroxyl groups, carboxyl groups, amino groups, nitrile groups, thiol groups, sulfonic acid groups, hydrocarbon oxygen carbonyl groups, haloformyl groups, carbamoyl groups, formyl groups, amide groups, and halogens.

[0007] The film-forming additive is preferably one or more of fluoroethylene carbonate, vinylene carbonate, ethylene carbonate, cyclopentane sulfone, γ-butyrolactone, vinyl sulfite, 1,3-propylene sultone, tetrahydrofuran, methyl ethyl sulfone, dimethyl sulfite, trimethyl phosphate, acrylonitrile, 2-nitrile furan, and trimethoxyborane.

[0008] In terms of mass fraction, the content of g-C3N4 accounts for 0.001%-5% of the total electrolyte mass, and preferably the content of g-C3N4 accounts for 0.01%-5% of the total electrolyte mass.

[0009] Calculated by weight, the content of the film-forming additive accounts for 0.01-30% of the total electrolyte weight.

[0010] The electrolyte additive is used in a lithium-ion battery, and the electrolyte additive is added to the electrolyte of the lithium-ion battery, and the electrolyte of the lithium-ion battery also includes a sodium salt and a non-aqueous organic solvent; the electrolyte additive can make the negative electrode material in the lithium-ion battery free of dendrites within 20-1000 cycles.

[0011] The negative electrode of the lithium ion battery is one or more of metallic lithium, graphite, silicon-based materials, hard carbon, amorphous carbon, and lithium titanate, and the positive electrode is lithium iron phosphate, lithium manganate, lithium cobaltate, LiNi(1-xy)Co x Mn y O2 (0≤x, y≤1), one or more of lithium-rich lithium manganese oxide, lithium iron manganese phosphate, and lithium titanate.

[0012] The electrolyte additive is used in a sodium ion battery, and the electrolyte additive is added to the electrolyte of the sodium ion battery, and the electrolyte of the sodium ion battery also includes a sodium salt and a non-aqueous organic solvent; the electrolyte additive can make the negative electrode material in the sodium ion battery free of dendrites within 50-1000 cycles.

[0013] The negative electrode of the sodium ion battery is one or more of metallic sodium, hard carbon, carbon black, amorphous carbon, graphite, SnS2, Na2Ti3O7, silicon-based materials, metal oxides, and metal sulfides; the positive electrode material is one or more of sodium manganate, sodium alum phosphate, sodium alum fluorophosphate, sodium iron phosphate, and sodium manganese phosphate.

[0014] The beneficial effects of the present invention are:

[0015] 1) The g-C3N4 in the electrolyte additive of the present invention is rich in -NH2 and has strong nucleophilic ability. It is easy to form hydrogen bonds with other components containing carbonyl bonds, ether bonds, hydroxyl groups, carboxyl groups and other groups. During the reduction process of the additive, nitrogen-containing organic components are formed and deposited on the surface of the battery negative electrode material to form a stable and conductive protective film, which evenly disperses the negative electrode electrons, enhances the electrochemical stability of the negative electrode, and ultimately improves the cycle stability of the battery.

[0016] 2) The electrolyte additive of the present invention can be used in lithium / sodium ion batteries, and is added as an electrolyte additive to the electrolyte of lithium / sodium ion batteries. The electrolyte additive can make the negative electrode material in the lithium ion battery free of dendrites within 20-1000 cycles, and can make the negative electrode material in the sodium ion battery free of dendrites within 50-1000 cycles. During the electrochemical reaction process, a negative electrode solid electrolyte interface film with good conductive performance is formed, which can inhibit the generation of lithium / sodium dendrites, achieve uniform deposition of lithium / sodium, and improve the battery rate and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a relationship diagram between the cycle capacity retention rate and the number of cycles of Comparative Example 2 and Example 7 of the present invention. DETAILED DESCRIPTION

[0018] The present invention is further explained below in conjunction with specific embodiments and drawings.

[0019] The battery cycle performance was tested using two control groups without electrolyte additives and eight examples containing electrolyte additives of different compositions as experimental groups, wherein the preparation method of the electrolyte additive of the present invention adopts the conventional means of natural reaction after mixing at room temperature.

[0020] Example 1: The present invention proposes an electrolyte additive for lithium or sodium ion batteries, wherein the electrolyte is a 1 mol / LLiPF6 solution of dimethyl carbonate DMC and diethyl carbonate DEC (50wt%:50wt%), and the electrolyte additive is 0.001wt% g-C3N4 and 0.2wt% vinyl sulfite. The electrolyte is tested in an NCM811 / Li battery, and no dendrites appear in the battery within 30 cycles, and the cycle retention rate after 200 cycles is 75.6%.

[0021] Example 2: The present invention proposes an electrolyte additive for lithium or sodium ion batteries, wherein the electrolyte is a PC solution of 1 mol / L NaClO4, and the electrolyte additive is 0.1 wt% g-C3N4 and 1 wt% vinylene carbonate. The electrolyte is tested in a Na3V2(PO4)3 / Na battery, and no dendrites appear in the battery within 50 cycles, and the cycle retention rate after 200 cycles is 90.5%.

[0022] Example 3: The present invention proposes an electrolyte additive for lithium or sodium ion batteries, wherein the electrolyte is a PC solution of 1 mol / L NaClO4, and the electrolyte additive is 0.15 wt% g-C3N4 and 2 wt% ethylene carbonate. The electrolyte is tested in a Na3V2(PO4)3 / Na battery, and no dendrites appear in the battery within 50 cycles, and the cycle retention rate after 200 cycles is 94.8%.

[0023] Example 4: The present invention proposes an electrolyte additive for lithium or sodium ion batteries, wherein the electrolyte is a PC solution of 1 mol / L NaClO4, and the electrolyte additive is 0.2 wt% g-C3N4 and 3 wt% fluoroethylene carbonate. The electrolyte is tested in a Na3V2(PO4)3 / Na battery, and no dendrites appear in the battery within 10 cycles, and the cycle retention rate after 200 cycles is 95.7%.

[0024] Embodiment 5:

[0025] The present invention proposes an electrolyte additive for lithium or sodium ion batteries, wherein the electrolyte is a PC solution of 1 mol / L NaClO4, and the electrolyte additive is 0.5 wt% of g-C3N4 and 0.01 wt% of fluoroethylene carbonate. The electrolyte is tested in a Na3V2(PO4)3 / Na battery, and no dendrites appear in the battery within 200 cycles, and the 200-week cycle retention rate is 91.3%.

[0026] Example 6: The present invention proposes an electrolyte additive for lithium or sodium ion batteries, wherein the electrolyte is a PC solution of 1 mol / L NaClO4, and the electrolyte additive is 1 wt% g-C3N4 and 5 wt% fluoroethylene carbonate. The electrolyte is tested in a Na3V2(PO4)3 / Na battery, and no dendrites appear in the battery within 1000 cycles, and the cycle retention rate after 200 cycles is 96.2%.

[0027] Example 7: The present invention proposes an electrolyte additive for lithium or sodium ion batteries, wherein the electrolyte is a PC solution of 1 mol / L NaClO4, and the electrolyte additive is 2.5 wt% g-C3N4 and 10 wt% fluoroethylene carbonate. The electrolyte is tested in a Na3V2(PO4)3 / Na battery, and no dendrites appear in the battery within 500 cycles, and the cycle retention rate after 200 cycles is 94.7%.

[0028] Embodiment 8:

[0029] The present invention proposes an electrolyte additive for lithium or sodium ion batteries, wherein the electrolyte is a 1 mol / L LiPF6 DMC and DEC (50 wt%:50 wt%) solution, and the electrolyte additive is 5 wt% g-C3N4 and 30 wt% fluoroethylene carbonate. The electrolyte is tested in a SiOx / Li battery, and no dendrites appear in the battery within 20 cycles, and the cycle retention rate after 200 cycles is 65.6%.

[0030] The preparation components and battery performance of Examples 1-8 are shown in Table 1:

[0031]

[0032] Comparative Example 1: The electrolyte and battery in Comparative Example 1 are prepared with the same ingredients as in Example 6, except that the electrolyte additive is 3% vinylene carbonate. The electrolyte is tested in a Na3V2(PO4)3 / Na battery, and dendrites appear in the battery within 1000 cycles, and the cycle retention rate after 200 cycles is 82.70%.

[0033] Comparative Example 2: The electrolyte and battery in Comparative Example 2 are prepared with the same ingredients as in Example 7, except that the electrolyte additive is 10% vinylene carbonate. The electrolyte is tested in a Na3V2(PO4)3 / Na battery, and dendrites appear in the battery within 500 cycles. The cycle retention rate after 200 cycles is 85.40%.

[0034] The preparation method and battery performance of the comparative example are shown in Table 2:

[0035] Additive ingredients and content / comparative ratio Comparative Example 1 Comparative Example 2 <![CDATA[g-C3N4]]> No No Fluoroethylene carbonate 10％ Vinylene carbonate 3％ Battery composition NVP / Na NVP / Na 200-week capacity retention rate 82.7％ 85.4％

[0036] Combining the above embodiments and comparative examples, it can be concluded that: by comparing 1 and embodiment 6, when g-C3N4 is not added, the cycle performance decreases from 96.2% to 82.7%; by comparing 2 and embodiment 7, when g-C3N4 is not added, the cycle performance decreases from 94.7% to 85.4%, indicating that a single additive is not sufficient to form a SEI film with better performance and cannot inhibit the growth of dendrites, thereby causing a decline in performance; after adding g-C3N4 to the electrolyte, the two participate in the film-forming reaction together under the synergistic effect of hydrogen bonds, which can better inhibit the growth of dendrites and promote the improvement of battery performance.

[0037] In combination with the above implementation cases, due to the joint complexation of g-C3N4 and film-forming additives, as an effective electrolyte additive, they can jointly promote the electrochemical stability of the battery, increase the battery cycle stability, and avoid the formation of metal dendrites. This beneficial effect is common in lithium batteries and sodium batteries.

[0038] The above description is only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A lithium or sodium ion battery electrolyte additive, characterized in that: The electrolyte additive includes g-C3N4 and a film-forming additive, and the g-C3N4 and the film-forming additive are coupled to form a negative electrode solid electrolyte interface film through intermolecular hydrogen bonding; the film-forming additive includes one or more organic substances containing carbonyl bonds, ether bonds, hydroxyl groups, carboxyl groups, amino groups, nitrile groups, thiol groups, sulfonic acid groups, hydrocarbon oxygen carbonyl groups, haloformyl groups, carbamoyl groups, formyl groups, amide groups, and halogens; In terms of mass fraction, the content of the g-C3N4 accounts for 0.01%-5% of the total electrolyte mass; the content of the film-forming additive accounts for 0.01%-30% of the total electrolyte mass.

2. The electrolyte additive for lithium or sodium ion batteries according to claim 1, characterized in that: The film-forming additive is preferably one or more of fluoroethylene carbonate, vinylene carbonate, ethylene carbonate, cyclopentane sulfone, γ-butyrolactone, vinyl sulfite, 1,3-propylene sultone, tetrahydrofuran, methyl ethyl sulfone, dimethyl sulfite, trimethyl phosphate, acrylonitrile, 2-nitrile furan, and trimethoxyborane.

3. The use of the electrolyte additive according to any one of claims 1-2 in a lithium ion battery, characterized in that: The electrolyte additive is added to the electrolyte of the lithium-ion battery, and the electrolyte of the lithium-ion battery also includes a sodium salt and a non-aqueous organic solvent; the electrolyte additive can make the negative electrode material in the lithium-ion battery free of dendrites within 20-1000 cycles.

4. The use according to claim 3, characterized in that: The negative electrode of the lithium-ion battery is one or more of metallic lithium, graphite, silicon-based materials, hard carbon, amorphous carbon, and lithium titanate, and the positive electrode is lithium iron phosphate, lithium manganate, lithium cobaltate, LiNi (1-x-y) Co x Mn y O2 (0≤x, y≤1), one or more of lithium-rich lithium manganese oxide, lithium iron manganese phosphate, and lithium titanate.

5. The use of the electrolyte additive according to any one of claims 1-2 in a sodium ion battery, characterized in that: The electrolyte additive is added into the electrolyte of the sodium ion battery, and the electrolyte of the sodium ion battery also includes sodium salt and non-aqueous organic solvent; the electrolyte additive can make the negative electrode material in the sodium ion battery free of dendrites within 50-1000 cycles.

6. The use according to claim 5, characterized in that: The negative electrode of the sodium ion battery is one or more of metallic sodium, hard carbon, carbon black, amorphous carbon, graphite, SnS2, Na2Ti3O7, silicon-based materials, metal oxides, and metal sulfides; the positive electrode material is one or more of sodium manganate, sodium alum phosphate, sodium alum fluorophosphate, sodium iron phosphate, and sodium manganese phosphate.

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