CN111293363A - A high-voltage nickel-manganate lithium-ion battery electrolyte and a secondary battery containing the electrolyte - Google Patents

Abstract

The invention provides a high-voltage nickel manganate lithium ion battery electrolyte and a secondary battery containing the electrolyte, belonging to the technical field of lithium ion battery electrolytes. The electrolyte is composed of the following raw materials by weight percentage: non-aqueous solvent 76-85%, electrolyte lithium salt 10-18%, electrolyte stabilizer 0.05-0.1%, dispersant 0.3-0.5%, negative electrode film-forming additive 2 ‑4% and positive electrode film-forming additive 0.5‑2%; the additive added in the electrolyte can form a uniform and stable solid-liquid interface film on the surface of the positive electrode and the negative electrode, so as to solve the problem of the existing spinel structure of lithium nickel manganate lithium ion The battery has poor cycle performance and cannot meet the technical problems of actual needs.

Description

A kind of high-voltage nickel manganate lithium ion battery electrolyte and secondary battery containing the electrolyte

【Technical field】

The present invention relates to the technical field of lithium-ion battery electrolyte, in particular to a high-voltage nickel-manganate lithium-ion battery electrolyte and a secondary battery containing the electrolyte.

【Background technique】

Compared with other batteries, lithium-ion batteries have the advantages of light weight, small size, high operating voltage, high energy density, high output power, high charging efficiency, no memory effect, and long cycle life, not only in mobile phones, notebook computers and other fields. It has been widely used, and is also considered to be one of the best choices for electric vehicles and large energy storage devices. However, at present, electronic digital products such as smart phones and tablet computers have higher and higher requirements on the energy density of batteries, making it difficult for commercial lithium-ion batteries to meet the requirements. The use of high-capacity cathode materials or high-voltage cathode materials is the most effective way to improve the energy density of lithium-ion batteries.

The high-voltage cathode materials that have been developed at this stage include spinel-type lithium nickel manganate LiNi _0.5 Mn _1.5 O ₄ (LNMO), lithium cobalt phosphate (LiCoPO4), lithium nickel phosphate (LiNiPO4), etc. The discharge platforms are 4.7 V, 4.8V and 5.1V, the charge cut-off voltage is higher than 4.5V. Among many cathode materials, spinel lithium nickel manganese oxide LiNi _0.5 Mn _1.5 O ₄ has received more and more attention due to its high potential to lithium (4.75Vvs.Li/Li+) and high specific capacity (147mAh/g) Multi-professional attention. However, traditional carbonate electrolytes have poor compatibility with LNMO materials, and an irreversible oxidative decomposition reaction will occur on the surface of highly oxidizing cathode materials. Moreover, under high voltage conditions, the cathode material will be continuously dissolved due to the continuous dissolution of transition metal ions, which will cause the cathode structure to be destroyed. , resulting in low coulombic efficiency and poor cycle life of the battery.

At present, researchers focus on using high-voltage additives or film-forming additives to improve the working voltage of electrolytes. Among them, the principle of action of the film-forming additive is that it is oxidized before the carbonate, and a protective film is formed on the surface of the electrode to prevent the further oxidative decomposition of the electrolyte, and can also protect the structure of the electrode material from being damaged. The Chinese invention patent with publication number CN107293789A discloses a lithium ion battery with good circulation effect and its electrolyte, including organic solvent, lithium salt and additives; the additives include monoisocyanate alkoxysilane compounds and film-forming compounds, The two act synergistically with each other to form a stable SEI film on the surface of some electrode materials to avoid the decomposition of the electrolyte on the electrode surface, but the cycle performance of the final battery is less than 80% when cycled for 200 cycles. poor. One possible reason is that the structure of the solid-liquid interface film formed by it is not uniform and stable enough. The solid-liquid interface film with a uniform and stable structure can allow lithium ions to pass through uniformly, thereby ensuring the uniform and stable electrodeposition process. For the non-uniform solid-liquid interface film, lithium ions will rapidly shuttle at the defects and deposit on the lithium surface, forming local lithium deposition hot spots. If the mechanical strength of the solid-liquid interface film is low enough to resist the deformation caused by the uneven deposition of lithium, the solid-liquid interface film will rupture at the hot spot. At the crack, without the control of the solid-liquid interface film, lithium deposition proceeds more rapidly, and finally lithium dendrites are formed.

At present, the development of an electrolyte suitable for forming a uniform and stable solid-liquid interface film is an urgent need for the promotion and application of high-voltage lithium manganate lithium ion batteries.

[Content of the invention]

The purpose of the invention of the present invention is to: in view of the above-mentioned problems, to provide a high-voltage lithium nickel manganate lithium ion battery electrolyte and a secondary battery containing the electrolyte, the additives added in the electrolyte can be used in the positive electrode and the negative electrode. A uniform and stable solid-liquid interface film is formed on the surface, so as to solve the technical problem that the existing spinel structure lithium nickel manganate lithium ion battery has poor cycle performance and cannot meet actual needs.

In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

A high-voltage nickel manganate lithium ion battery electrolyte is composed of the following raw materials by weight percentage: 76-85% of non-aqueous solvent, 10-18% of electrolyte lithium salt, 0.05-0.1% of electrolyte stabilizer, dispersant 0.3-0.5%, negative electrode film-forming additive 2-4% and positive electrode film-forming additive 0.5-2%;

The dispersant is EFKA-4340 dispersant; the negative electrode film-forming additive is fluoropropionyl ethyl acetate, 1,2-bis(chloroacetate) with a volume ratio of (5-8):1:(3-5). Methoxy)ethane and bis(trifluoromethylsulfonyl)imide cobalt; the positive film-forming additive is trialkylphosphine, N(trimethylsilyl)ethylamine or 2-(trimethyl) silyl)ethylamine.

In the present invention, further preferably, the non-aqueous solvent is composed of one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC).

In the present invention, further preferably, the electrolyte lithium salt is any one of lithium hexafluorophosphate (LiPF ₆ ), lithium bisfluorosulfonimide (LFSI) and lithium perchlorate.

In the present invention, further preferably, the electrolyte stabilizer is sulfolane or n-butyl sulfone.

In the present invention, further preferably, the percentage of the negative electrode film-forming additive in the electrolyte is 3%.

In the present invention, further preferably, the percentage of the positive electrode film-forming additive in the electrolyte is 1.0%.

The present invention also provides a method for preparing the above-mentioned high-voltage lithium nickel manganate lithium ion battery electrolyte, comprising the following steps:

(1) take by weighing non-aqueous organic solvent, electrolyte solution stabilizer and dispersant, under the environment that temperature is 25 ± 1 ℃, described non-aqueous organic solvent and dispersant are stirred to obtain solvent dispersion;

(2) taking by weighing the electrolyte lithium salt, slowly adding the electrolyte lithium salt to the solvent dispersion, stirring until the lithium salt is completely dissolved to form a transparent solution;

(3) taking by weighing the negative electrode film-forming additive, slowly adding the negative electrode film-forming additive to the dispersion liquid dissolved with the lithium salt, stirring, and standing to obtain an electrolyte precursor;

(4) When in use, the positive electrode film-forming additive is mixed with the electrolyte precursor solution, and stirred evenly to obtain the electrolyte solution.

In the present invention, further preferably, the steps (1)-(4) are all performed in a closed glove box in an Ar environment, and the water value in the glove box is less than 0.01 ppm and the oxygen value is less than 0.01 ppm.

The present invention also provides a 5V high-voltage lithium nickel manganate lithium ion battery, the positive electrode material is lithium nickel manganese oxide, the negative electrode material is lithium sheet, and the electrolyte of the lithium ion battery is any one of claims 1-7. the described electrolyte.

Owing to adopting the above-mentioned technical scheme, the beneficial effects of the present invention are:

1. A negative electrode film-forming additive is added to the electrolyte of the present invention, which contains fluoropropionyl ethyl acetate, 1,2-bis(chloromethoxy)ethane and bis(trifluoromethylsulfonyl)imide Cobalt, before the carbonate is oxidized, due to the oxidizing property of its cobalt ions, when bis(trifluoromethylsulfonyl)imide cobalt contacts with the cathode lithium sheet, an ion replacement reaction will occur, and a large number of ions are formed on the surface of the lithium sheet. Cobalt nanoparticles can further induce orderly nucleation of lithium ions during the deposition process, enabling subsequent dense deposition and avoiding local dendrite growth. At the same time, when the cobalt ions are reduced, free lithium ions will be replaced on the surface of the lithium sheet. The lithium interface further evolves into a lithium fluoride-rich SEI film during battery cycling, which plays a very good role in protecting the lithium cathode.

2. A positive film-forming additive is added to the electrolyte of the present invention, which contains trialkylphosphine, N(trimethylsilyl)ethylamine or 2-(trimethylsilyl)ethylamine, wherein the Both N and P have lone electron pairs. Before the carbonates are oxidized, they are easily complexed with transition metals to form phosphorus-metal bonds or N-metal bonds, which are closely attached to the surface of the positive electrode material to form a CEI film and lock the transition metal on the surface. The external alkyl group is simultaneously polymerized with carbonate and electrolyte lithium salt in the solvent to form the outer layer of the CEI film, which effectively prevents the electrolyte from directly contacting the positive electrode material, inhibits the dissolution of the cathode transition metals (Ni, Mn), and improves the overall internal battery. System stability.

3. An appropriate amount of EFKA-4340 dispersant is also added to the electrolyte of the present invention to improve the stability and uniformity of the electrolyte system, so that the SEI film and CEI film obtained by the reaction are more uniform and dense, and have higher structural strength , to avoid the local rupture of the solid-liquid interface protective film due to the uneven structure, and the formation of lithium dendrites at the cracks.

To sum up, the electrolyte of the present invention can form a dense solid-liquid interface protective film on the surface of the negative electrode and the surface of the positive electrode by adding the film-forming additive for the negative electrode and the film-forming additive for the positive electrode, and an appropriate amount of dispersant is added to the system, The structure of the solid-liquid interface protective film is uniform and stable, and the protective effect is further improved. Therefore, using the electrolyte of the present invention, the working voltage range of 5V high-voltage lithium manganate lithium ion battery can reach 3.5-4.9V; cycle 1500 at 2C rate The capacity retention rate reaches 90% after the first cycle; the capacity retention rate after 1000 cycles at 3C rate reaches 83.0%. The electrolyte provided by the invention is used for 5V high-voltage lithium nickel manganese oxide lithium ion battery, and has good cycle performance and capacity retention.

【Detailed ways】

In order to express the present invention more clearly, the present invention will be further described below through specific examples.

Example 1

A high-voltage nickel manganate lithium ion battery electrolyte is composed of the following raw materials by weight percentage: 76% of non-aqueous solvent, 18% of electrolyte lithium salt lithium hexafluorophosphate (LiPF ₆ ), 0.1% of electrolyte stabilizer sulfolane, EFKA- 4340 dispersant 0.5%, negative electrode film-forming additive 3.4% and positive electrode film-forming additive 2%; wherein, the negative electrode film-forming additive is fluoropropionyl ethyl acetate, 1,2-bis( Chloromethoxy)ethane and bis(trifluoromethylsulfonyl)imide cobalt; positive film-forming additive is trialkylphosphine. The non-aqueous solvent is composed of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:5.

The preparation method of the above-mentioned high-voltage nickel-manganate lithium-ion battery electrolyte comprises the following steps:

(1) In a closed glove box with an Ar environment, a water value of less than 0.01 ppm, an oxygen value of less than 0.01 ppm, and a temperature of 25±1° C., weigh the non-aqueous organic solvent, electrolyte stabilizer and dispersant, and weigh the non-aqueous organic solvent, electrolyte stabilizer and dispersant. Aqueous organic solvent and dispersant are stirred evenly to obtain solvent dispersion;

(2) taking by weighing the electrolyte lithium salt, slowly adding the electrolyte lithium salt to the solvent dispersion, stirring until the lithium salt is completely dissolved to form a transparent solution;

(3) taking by weighing the negative electrode film-forming additive, slowly adding the negative electrode film-forming additive to the dispersion liquid dissolved with the lithium salt, stirring, and standing to obtain an electrolyte precursor;

(4) When in use, the positive electrode film-forming additive is mixed with the electrolyte precursor solution, and stirred evenly to obtain the electrolyte solution.

Example 2

A high-voltage nickel-manganate lithium-ion battery electrolyte is composed of the following raw materials by weight percentage: 80% of a non-aqueous solvent, 15% of lithium bisfluorosulfonimide (LFSI) as an electrolyte, and 0.05% of an electrolyte stabilizer sulfolane. %, EFKA-4340 dispersant 0.35%, negative electrode film-forming additive 3.6% and positive electrode film-forming additive 1%; negative electrode film-forming additive is fluoropropionyl ethyl acetate with a volume ratio of 6:1:4, 1,2- Bis(chloromethoxy)ethane and bis(trifluoromethylsulfonyl)imide cobalt; the positive film-forming additive is trialkylphosphine. The non-aqueous solvent is composed of ethylene carbonate (EC) and methyl ethyl carbonate (EMC) in a volume ratio of 1:6.

The preparation method of the above-mentioned high-voltage nickel-manganate lithium-ion battery electrolyte comprises the following steps:

(1) In a closed glove box with an Ar environment, a water value of less than 0.01 ppm, an oxygen value of less than 0.01 ppm, and a temperature of 25±1° C., weigh the non-aqueous organic solvent, electrolyte stabilizer and dispersant, and weigh the non-aqueous organic solvent, electrolyte stabilizer and dispersant. Aqueous organic solvent and dispersant are stirred evenly to obtain solvent dispersion;

(2) taking by weighing the electrolyte lithium salt, slowly adding the electrolyte lithium salt to the solvent dispersion, stirring until the lithium salt is completely dissolved to form a transparent solution;

(3) taking by weighing the negative electrode film-forming additive, slowly adding the negative electrode film-forming additive to the dispersion liquid dissolved with the lithium salt, stirring, and standing to obtain an electrolyte precursor;

(4) When in use, the positive electrode film-forming additive is mixed with the electrolyte precursor solution, and stirred evenly to obtain the electrolyte solution.

Example 3

A high-voltage nickel-manganate lithium-ion battery electrolyte is composed of the following raw materials by weight percentage: 85% of non-aqueous solvent, 10% of lithium perchlorate, 0.1% of electrolyte stabilizer sulfolane or n-butylsulfone, EFKA- 4340 dispersant 0.4%, negative electrode film-forming additive 4% and positive electrode film-forming additive 0.5%; negative electrode film-forming additive is fluoropropionyl ethyl acetate, 1,2-bis(chloromethyl) with a volume ratio of 6:1:3 oxy)ethane and cobalt bis(trifluoromethylsulfonyl)imide; the positive film-forming additive is N(trimethylsilyl)ethylamine. The non-aqueous solvent is composed of a mixture of dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC) in a volume ratio of 1:1.

The preparation method of the above-mentioned high-voltage nickel-manganate lithium-ion battery electrolyte comprises the following steps:

(1) In a closed glove box with an Ar environment, a water value of less than 0.01 ppm, an oxygen value of less than 0.01 ppm, and a temperature of 25±1° C., weigh the non-aqueous organic solvent, electrolyte stabilizer and dispersant, and weigh the non-aqueous organic solvent, electrolyte stabilizer and dispersant. Aqueous organic solvent and dispersant are stirred evenly to obtain solvent dispersion;

(2) taking by weighing the electrolyte lithium salt, slowly adding the electrolyte lithium salt to the solvent dispersion, stirring until the lithium salt is completely dissolved to form a transparent solution;

(3) taking by weighing the negative electrode film-forming additive, slowly adding the negative electrode film-forming additive to the dispersion liquid dissolved with the lithium salt, stirring, and standing to obtain an electrolyte precursor;

(4) when in use, mix the positive electrode film-forming additive with the electrolyte precursor solution, and stir evenly to obtain the electrolyte solution

Example 4

A high-voltage nickel-manganate lithium-ion battery electrolyte is composed of the following raw materials in percentage by weight: 82% of non-aqueous solvent, 17% of electrolyte lithium salt bisfluorosulfonimide (LFSI), electrolyte stabilizer Sulfolane 0.1%, EFKA-4340 dispersant 0.3%, negative electrode film-forming additive 3% and positive electrode film-forming additive 2%; negative electrode film-forming additive is fluoropropionyl ethyl acetate with a volume ratio of 5:1:5, 1, 2-bis(chloromethoxy)ethane and bis(trifluoromethylsulfonyl)imide cobalt; positive film-forming additive is 2-(trimethylsilyl)ethylamine. The non-aqueous solvent is composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) in a volume ratio of 1:1:1.

The preparation method of the above-mentioned high-voltage nickel-manganate lithium-ion battery electrolyte comprises the following steps:

(1) In a closed glove box with an Ar environment, a water value of less than 0.01 ppm, an oxygen value of less than 0.01 ppm, and a temperature of 25±1° C., weigh the non-aqueous organic solvent, electrolyte stabilizer and dispersant, and weigh the non-aqueous organic solvent, electrolyte stabilizer and dispersant. Aqueous organic solvent and dispersant are stirred evenly to obtain solvent dispersion;

(2) taking by weighing the electrolyte lithium salt, slowly adding the electrolyte lithium salt to the solvent dispersion, stirring until the lithium salt is completely dissolved to form a transparent solution;

(3) taking by weighing the negative electrode film-forming additive, slowly adding the negative electrode film-forming additive to the dispersion liquid dissolved with the lithium salt, stirring, and standing to obtain an electrolyte precursor;

(4) when in use, mix the positive electrode film-forming additive with the electrolyte precursor solution, and stir evenly to obtain the electrolyte solution

Comparative Example 1

The difference between this comparative example and Example 2 is that the negative electrode film-forming additives are fluoropropionyl ethyl acetate and 1,2-bis(chloromethoxy)ethane with a volume ratio of 10:1, without bis(trimethyl)ethane Fluoromethylsulfonyl)imide cobalt.

Comparative Example 2

The difference between this comparative example and Example 2 is that the negative film-forming additives are 1,2-bis(chloromethoxy)ethane and bis(trifluoromethylsulfonyl)imide cobalt with a volume ratio of 1:10, Does not contain ethyl fluoropropionyl acetate.

Comparative Example 3

The difference between this comparative example and Example 2 is that the EFKA-4340 dispersant is replaced by a non-aqueous solvent, that is, it does not contain a dispersant.

Comparative Example 4

The difference between this comparative example and Example 2 is that the positive electrode film-forming additive is replaced by the same amount of non-aqueous solvent, that is, the positive electrode film-forming additive is not included.

Comparative Example 5

The difference between this comparative example and Example 2 is that the negative electrode film-forming additive is replaced by the same amount of non-aqueous solvent, that is, the positive electrode film-forming additive is not included.

Comparative Example 6

Both the positive electrode film-forming additive and the negative electrode film-forming additive were replaced by the same amount of non-aqueous solvent.

The 10 kinds of electrolytes provided in the above-mentioned Examples 1-4 and Comparative Examples 1-6 were respectively applied to lithium ion batteries, with lithium nickel manganate (LNMO) as the positive electrode and lithium sheet (Li) as the negative electrode, and the electrolyte was injected into the battery. After sealing, a 18650-type cylindrical battery was made, and 10 kinds of lithium-ion batteries with different electrolytes were obtained. After the prepared batteries were stored at a constant temperature of 25 °C for 24 hours, they were charged and discharged at a current of 0.2C for 2 weeks to form a stable battery. Solid-liquid interface protective film. The following experiments were performed on the batteries obtained from all Examples 1-4 and all Comparative Examples 1-6:

Normal temperature cycle experiment: under the condition of 25℃±3℃, charge the battery to 4.95V with 1C rate constant current-constant voltage, and the cut-off current is 0.05C; then discharge to 3.0V with 1C constant current to complete a 1C charge Discharge cycle; repeat the above-mentioned charge and discharge process, divide the 300th discharge capacity by the first discharge capacity to obtain the capacity retention rate of 300 cycles, and the recorded results are shown in Table 1.

It can be seen from the test results in Table 1 that the electrolytes provided in Examples 1-4 of the present invention were applied to high-voltage lithium nickel manganate lithium batteries, and after 300 cycles, the capacity retention rate was over 89.3%, while the comparative example 1-6 lacks necessary film-forming additives or dispersants, and its capacity retention rate is not as good as that of the present invention. The high-voltage electrolyte for lithium-ion batteries provided by the present invention can greatly improve the performance of lithium-ion batteries under high voltage conditions. The cycle performance is conducive to the promotion and application of lithium nickel manganate lithium ion batteries.

The above description is a detailed description of the preferred feasible embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications completed under the technical spirit suggested by the present invention shall belong to This invention covers the scope of the patent.

Claims (9)

1. The high-voltage lithium nickel manganese oxide lithium ion battery electrolyte is characterized by comprising the following raw materials in percentage by weight: 76-85% of non-aqueous solvent, 10-18% of electrolyte lithium salt, 0.05-0.1% of electrolyte stabilizer, 0.3-0.5% of dispersant, 2-4% of negative film-forming additive and 0.5-2% of positive film-forming additive;

the dispersant is EFKA-4340 dispersant; the negative electrode film forming additive is prepared from (5-8) by volume: 1: (3-5) ethyl levulinylacetate, 1, 2-bis (chloromethoxy) ethane, and bis (trifluoromethylsulfonyl) cobalt imide; the positive film-forming additive is trialkylphosphine, N (trimethylsilyl) ethylamine or 2- (trimethylsilyl) ethylamine.

2. The electrolyte of claim 1, wherein: the non-aqueous solvent is composed of one or more of Ethylene Carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC).

3. The electrolyte of claim 1, wherein: the electrolyte lithium salt lithium hexafluorophosphate (LiPF)₆) Lithium bis (fluorosulfonyl) imide (LFSI) and lithium perchlorate.

4. The electrolyte of claim 1, wherein: the electrolyte stabilizer is sulfolane or n-butyl sulfone.

5. The electrolyte of claim 1, wherein: the percentage of the negative film forming additive in the electrolyte is 3%.

6. The electrolyte of claim 1, wherein: the percentage of the film forming additive of the positive electrode in the electrolyte is 1.0%.

7. The method of preparing a high voltage lithium nickel manganese oxide lithium ion battery electrolyte according to any one of claims 1 to 6, comprising the steps of:

(1) weighing a non-aqueous organic solvent, an electrolyte stabilizer and a dispersant, and uniformly stirring the non-aqueous organic solvent and the dispersant at the temperature of 25 +/-1 ℃ to obtain a solvent dispersion liquid;

(2) weighing electrolyte lithium salt, slowly adding the electrolyte lithium salt into the solvent dispersion liquid, and stirring until the lithium salt is completely dissolved to form a transparent solution;

(3) weighing a negative electrode film forming additive, slowly adding the negative electrode film forming additive into a dispersion liquid in which lithium salt is dissolved, stirring, and standing to obtain an electrolyte precursor liquid;

(4) when in use, the anode film-forming additive is mixed with the electrolyte precursor solution, and the mixture is uniformly stirred to obtain the electrolyte.

8. The method for preparing the electrolyte according to claim 7, characterized in that: and (3) performing steps (1) to (4) in an Ar environment in a closed glove box, wherein the water value in the glove box is less than 0.01ppm, and the oxygen value is less than 0.01 ppm.

9. A5V high-voltage lithium nickel manganese oxide lithium ion battery, wherein the positive electrode material is lithium nickel manganese oxide, the negative electrode material is a lithium sheet, and the electrolyte of the lithium ion battery is the electrolyte of any one of claims 1 to 7.