CN114824281A

CN114824281A - Lithium ion battery and preparation method thereof

Info

Publication number: CN114824281A
Application number: CN202210745804.9A
Authority: CN
Inventors: 马娟; 卞亚娟; 姜鹏程; 许淑义; 郑春龙
Original assignee: Tianpeng Lithium Energy Technology Huai'an Co ltd
Current assignee: Tianpeng Lithium Energy Technology Huai'an Co ltd
Priority date: 2022-06-29
Filing date: 2022-06-29
Publication date: 2022-07-29
Anticipated expiration: 2042-06-29
Also published as: CN114824281B

Abstract

The invention provides a lithium ion battery and a preparation method thereof, and relates to the technical field of lithium ion batteries. Specifically, the battery mainly comprises a positive electrode, a negative electrode, an electrolyte and a diaphragm; wherein the negative electrode comprises graphite, a silicon-oxygen material and a binder, and the binder comprises an acrylate compound; the electrolyte includes a cyano compound. According to the invention, the short circuit safety problem of the silicon-containing negative electrode is solved by adding the olefinic acid ester binder, the olefinic acid ester binder has strong binding force on the expansion of the negative electrode, and the increase of the thickness of the negative electrode plate in the circulation process can be well inhibited, so that the safety risk caused by the expanded electrode plate is reduced; meanwhile, the cyanide additive is used in the electrolyte, so that the negative effect caused by the acrylate binder is solved, and the overall cycle and storage safety performance of the battery is greatly improved.

Description

Lithium ion battery and preparation method thereof

Technical Field

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

Background

In recent years, lithium ion secondary batteries have become more and more widely used in the fields of mobile phones, computers, energy storage, electric tools, and electric automobiles. In use, it has been one of the goals pursued to have higher energy density and cycle life. In order to realize higher energy density, silicon-containing negative electrode materials are gradually developed and applied to lithium ion batteries, because the gram capacity of the silicon-containing negative electrode is higher, the higher battery capacity can be realized under the same design volume, and the energy density of the battery is greatly improved.

However, due to the characteristics of the crystal structure of the silicon material, about 300% of volume expansion can be brought in the charging process, silicon particles can be cracked and pulverized due to the large volume expansion and contraction in the circulating process, a solid electrolyte layer is continuously formed on the generated new surface, lithium ions are continuously consumed, and the problem of rapid decay of the cycle life is further caused. Meanwhile, the thickness of the pole piece is continuously increased due to continuous irreversible expansion, the pole piece can be bent and broken due to uneven stress release inside the battery cell, and the broken pole piece pierces through the diaphragm to cause short circuit, so that the safety problem is solved. Therefore, there is a need for a new lithium ion battery that addresses the series of inherent problems of batteries caused by silicon by optimizing the electrode or electrolyte composition.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The first purpose of the invention is to provide a lithium ion battery, which is used for solving the technical problems of battery cycle life and safety caused by volume expansion and contraction generated by the crystal structure characteristics of silicon materials in the prior art; by limiting the types of the negative electrode adhesive and the electrolyte additive, the storage performance of the silicon-containing battery is improved while the safety performance of the silicon-containing battery is ensured.

The second purpose of the invention is to provide a preparation method of the lithium ion battery.

In order to achieve the above purpose of the present invention, the following technical solutions are adopted:

a lithium ion battery comprises a positive electrode, a negative electrode, electrolyte and a diaphragm; wherein the negative electrode comprises graphite, a silicon-oxygen material and a binder, and the binder comprises an acrylate compound; the electrolyte includes a cyano compound.

Research shows that when the acrylate adhesive is adopted in the lithium ion battery, the cyclic short circuit condition can be effectively reduced, but the storage performance of the battery can be greatly deteriorated by the acrylate compound. Specifically, the acrylate-based compound has more branches, which increases the active specific surface area of the negative electrode and causes more side reactions, and the gas yield further increases when the side reactions increase, and deteriorates the storage property. When the dosage of the adhesive is increased, the negative effects are further enhanced, and the larger specific surface area can cause more side reactions to consume lithium ions in the circulation process, so that the circulation retention rate is reduced, and the gas generation side reaction caused in the high-temperature storage process is increased.

However, when a cyano compound is further added into the electrolyte on the basis of the acrylate binder, the cyano compound and the negative electrode undergo an oxidation reaction earlier, a reduction product is deposited on the surface of the negative electrode, and the gas production reaction of the acrylate compound and the electrolyte is prevented; on the other hand, the cyano compound can be complexed with transition metal on the surface of the positive electrode, so that the interface of the positive electrode is stabilized, and the gas generation reaction caused by oxygen release of the positive electrode is reduced. Therefore, by utilizing the principle of complementary synergy of the acrylate compound and the cyano compound, the potential safety hazard possibly caused by electrode plate deformation can be avoided while the problems of cycle life attenuation and the like caused by volume expansion and contraction of the negative electrode silicon are solved.

Preferably, the acrylate compound comprises at least one of the following structural formulas A1-A9;

A1、

A2、

A3、

A4、

A5、

A6、

A7、

A8、

A9。

the structure of the acrylate compound can influence the action effect, and particularly, when the number of carboxyl and carbon-oxygen bonds in the structural formula is more, the binding force on the negative electrode is stronger, and the cycle life of the battery is also better; at the same time, however, the above-mentioned negative effects are also stronger, i.e., more gas-generating side reactions are induced during storage, and high-temperature storage performance is deteriorated. In addition, when the reducibility of the unsaturated bond in the acrylate compound is stronger, the gas generation side reaction is increased correspondingly.

Preferably, the negative electrode further includes a thickener; the thickening agent comprises hydroxymethyl cellulose, hydroxymethyl cellulose salt (such as hydroxymethyl cellulose lithium and hydroxymethyl cellulose sodium), hydroxyethyl cellulose and its salt, hydroxypropyl methylcellulose and its salt, butylbenzene latex, etc.;

the acrylate organic matter contains more carboxyl and carbon-oxygen bonds, and when the thickening component exists in the negative electrode, the acrylate organic matter and the thickening agent have stronger binding force, so that stronger binding force exists on the expansion of the negative electrode pole piece, and the phenomenon of cycle short circuit caused by the expansion of the pole piece is further relieved.

Preferably, in the negative electrode, the mass ratio of the binder, the silica material, and the graphite is (0.01 to 5): (1-99): (0.01-98.9);

more preferably, in the negative electrode, the mass ratio of the binder, the silica material, and the graphite is (0.1 to 3): (1-80): (0.01-98.9).

The cyano compound comprises at least one of the following structural formulas B1-B12;

B1、

B2、

B3、

B4、

B5、

B6、

B7、

B8、

B9、

B10、

B11、

B12；

cyano compounds having different structures have different effects on functions of a battery such as storage or recycling, depending on the number of cyano groups in the compound and the size or length of a molecular chain. Specifically, the method comprises the following steps: when the number of the cyano-groups is more, for example, the cyano-compound B6 is more compact in an interfacial film formed by a negative reduction product, is more stable in the storage process and has better inhibition on gas generation during storage; meanwhile, when the amount of the complex of the cyano compound and the transition metal ions on the surface of the anode is more and the efficiency is higher, the inhibition on stored gas production is stronger. When the molecular chain is longer, such as cyano compound B5, the cyano molecules at both ends of the chain can complex transition metals at the same time due to the better flexibility of the molecular chain; when the molecular chain is short, for example, cyano compound B2, only the cyano group at one end of the chain may act, and the ability to suppress side reactions may be weak.

It is to be noted, however, that the interfacial film formation of the cyano compound leads to an increase in the resistance of the battery, which increases the polarization during charge and discharge and causes a capacity loss, and particularly when the content of the cyano compound is increased, the loss of polarized capacity due to the increase in resistance is further deteriorated, i.e., the loss of cyclic capacity is increased and the cycle life is reduced; therefore, the amount of the cyano compound added to the electrolytic solution must be controlled within the following range;

preferably, the mass content of the cyano compound in the electrolyte is 0.01-5%;

more preferably, when the cyano compound is a specific compound of the following several types, the following more preferable mass contents may be employed:

when the cyano compound is acetonitrile or butanedinitrile, the mass content of the cyano compound in the electrolyte is 0.05% -5%;

when the cyano compound is one of adiponitrile, 1, 2-bis (cyanoethoxy) ethane or 1, 4-dicyano-2-butene, the mass content of the cyano compound in the electrolyte is 0.05% -3%;

when the cyano compound is one of cyclohexane-1, 4-dicyan or hexanetricarbonitrile, the mass content of the cyano compound in the electrolyte is 0.05-2%.

Preferably, the electrolyte includes a lithium salt, an organic solvent, and the cyano compound;

more preferably, the lithium salt comprises lithium hexafluorophosphate.

Preferably, the organic solvent comprises a linear ester and/or a cyclic ester;

more preferably, the linear ester comprises at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, ethyl propionate, methyl propionate, propyl propionate, and methyl acetate;

more preferably, the mass content of the linear ester in the electrolyte is 40.00-80.75%;

preferably, the cyclic ester includes at least one of ethylene carbonate and propylene carbonate;

more preferably, the mass content of the cyclic ester in the electrolyte is 12.00-47.50%.

Preferably, the electrolyte further comprises an additive; the additive comprises at least one of vinylene carbonate, ethylene carbonate, fluoro carbonate, 1, 3-propane sultone, 1, 3-propene sultone, 2, 4-butane sultone, methylene methane disulfonate, lithium difluoro oxalate borate, lithium dioxalate borate, lithium tetrafluoroborate, lithium bis fluoro sulfonyl imide, lithium bis trifluoro methane sulfonyl imide and lithium difluoro phosphate.

Preferably, the positive electrode comprises a ternary material; the structural formula of the ternary material is LiNi _x Co _y Mn _z O ₂ Wherein x + y + z = 1.

Preferably, the separator comprises a porous polymer film having a pore size of 500 nm or less; when the pore diameter of the diaphragm is above a limit value, the overlarge pore diameter can cause self-discharge of the battery;

more preferably, the porous polymer film includes at least one of polyethylene, polypropylene, a ceramic-coated membrane, an aramid-coated membrane, and a polyethylene-polypropylene composite membrane.

The preparation method of the lithium ion battery comprises the following steps:

and assembling the anode, the cathode and the diaphragm, injecting electrolyte, and packaging to obtain the lithium ion battery.

Preferably, the preparation method of the electrolyte comprises the following steps:

and fully mixing all components forming the electrolyte to obtain the electrolyte.

Preferably, the preparation method of the negative electrode comprises the following steps:

fully mixing graphite, a silica material and a binder to obtain a negative electrode slurry, and coating and performing high-temperature treatment to obtain the negative electrode;

more preferably, a conductive agent is further added to the negative electrode slurry; the conductive agent comprises at least one of acetylene black, carbon fiber, carbon nano tube and graphene;

further preferably, the preparation method of the negative electrode specifically comprises the following steps:

and fully mixing the graphite, the silica material, the adhesive, the conductive agent and the thickening agent to obtain negative electrode slurry, and coating, baking, rolling and cutting to obtain the negative electrode.

Preferably, the preparation method of the positive electrode comprises the following steps:

fully mixing a positive electrode material and a binder to obtain positive electrode slurry, and coating and performing high-temperature treatment to obtain the positive electrode;

more preferably, a conductive agent is also added to the positive electrode slurry; the conductive agent comprises at least one of acetylene black, carbon fiber, carbon nano tube and graphene;

the preparation method of the anode specifically comprises the following steps:

and fully mixing the positive electrode material, the conductive agent and the binder to obtain positive electrode slurry, and coating, baking, rolling and cutting to obtain the positive electrode.

The preparation method of the lithium ion battery, the preparation method of the electrolyte, the preparation method of the anode and the preparation method of the cathode can also comprise other conventional pretreatment or post-treatment operations, which are not described in detail in the invention.

Compared with the prior art, the invention has the beneficial effects that:

(1) according to the lithium ion battery provided by the invention, the acrylate binder is added, so that a strong binding force can be exerted on the expansion of a silica material in a negative electrode material, the increase of the thickness of a negative electrode piece in a circulation process can be well inhibited, and the short circuit risk caused by the expanded electrode piece is further reduced; meanwhile, the problem of increase of stored gas generated caused by the acrylate binder is solved better by adding the cyano compound, and the negative binder with a specific structure is combined with the electrolyte, so that the storage performance of the lithium ion battery can be improved while the cycle safety guarantee of the silicon-containing battery is remarkably improved.

(2) The preparation method of the lithium ion battery provided by the invention is simple and easy to implement, has good reproducibility, is easy for mass production to obtain a large amount of high-safety lithium ion batteries, and has good market application prospect.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a graph comparing the cycle performance of examples of the present invention with that of comparative examples;

FIG. 2 is a graph comparing coulombic efficiencies of examples of the present invention and comparative examples.

Detailed Description

The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and the detailed description, but those skilled in the art will understand that the following described embodiments are some, not all, of the embodiments of the present invention, and are only used for illustrating the present invention, and should not be construed as limiting the scope of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The invention is implemented by the following specific modes:

a lithium ion battery comprises a positive electrode, a negative electrode, electrolyte and a diaphragm; the negative electrode comprises graphite, a silica material and a binder, wherein the binder comprises an acrylate compound; the electrolyte includes a cyano compound.

In a preferred embodiment, in the negative electrode, a mass ratio of the binder, the silica material, and the graphite is (0.01 to 5): (1-99): (0.01-98.9); in a more preferred embodiment, in the negative electrode, a mass ratio of the binder, the silica material, and the graphite is (0.1 to 3): (1-80): (0.01-98.9);

as a more preferred embodiment, in the negative electrode, the mass content of the binder is 0.01% to 5% by mass, including but not limited to 0.01%, 0.05%, 0.1%, 0.25%, 0.5%, 0.75%, 1%, 1.25%, 1.5%, 1.75%, 2%, 2.25%, 2.5%, 2.75%, 3%, 3.5%, 4%, 4.5%, 5%;

as a more preferred embodiment, in the negative electrode, the mass content of the silicon oxygen material is 1% to 99% by mass, including but not limited to 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%;

as a more preferred embodiment, in the negative electrode, the graphite is contained in an amount of 0.01% to 98.9% by mass, including but not limited to 0.01%, 0.05%, 0.1%, 0.25%, 0.5%, 0.75%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98.9% by mass.

As a preferred embodiment, the mass content of the cyano compound in the electrolyte solution includes, but is not limited to, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3.3%, 3.4%, 3.5%, 3.4%, 4.5%, 4.4%, 4.6%, 3.4%, 4%, 4.5%, 4.4%, 4%, 4.6%, 3.6%, 3.4%.

As a preferred embodiment, the organic solvent comprises a linear ester and/or a cyclic ester; wherein, the mass content of the linear ester in the electrolyte comprises but is not limited to 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% and 80.75%; the mass content of the cyclic ester in the electrolyte is 12%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 47.75%.

In all of the following examples and comparative examples, the acrylic adhesives A1 to A9 and the cyano compounds B1 to B12 correspond to the structural formulae described in the summary of the invention.

It should be noted that the acrylic adhesives a1 to a9 in all of the following examples and comparative examples can be supplied by any manufacturer as long as the structural formulas are consistent with those described in the present specification. It can also be synthesized by itself, and a feasible synthetic route is given below.

It should be noted that the synthetic routes given below do not mean that the acrylate adhesives A1-A9 can be synthesized only by the following routes; the acrylic adhesives A1-A9 can be prepared by any feasible synthetic route by those skilled in the art as long as the structural formula of the final product is consistent with the content recorded in the specification of the invention.

(1) Synthetic route of a 1: 10g of monomers (A) are successively reacted at room temperature

) 50g of DMF, 0.15g of initiator containing terminal groups (

) Adding into a flask, stirring well, introducing N ₂ To discharge the air (oxygen) in the reaction system, heating the reaction system to 60 ℃ after 2h, and continuously reacting for 6 h; the mixture was then poured into ether to precipitate the polymer, and the washing operation was repeated three times, followed by drying and obtaining a 1.

(2) Synthetic route of a 2: sequentially reacting at room temperature

) A second monomer (a)

) DMF, initiators containing terminal groups (liquid ethane, C) ₂ H ₆ ) Adding into a 200mL flask, stirring uniformly, and introducing N ₂ To discharge the air (oxygen) in the reaction system, heating the reaction system to 60 ℃ after 2h, and continuously reacting for 6 h; the mixture was then poured into ether to precipitate the polymer, and the washing operation was repeated three times, followed by drying and obtaining a 2.

(3) Synthetic route of a 3: essentially the same as a2, except that: the initiator is

。

(4) Synthetic route of a 4: essentially the same as a2, except that: monomer is

。

(5) Synthetic route of a 5: essentially the same as a4, except that: the amounts of the monomers and the second monomer added were adjusted.

(6) Synthetic route of a 6: essentially the same as a2, except that: monomer is

。

(7) Synthetic route of a 7: essentially the same as a2, except that: the monomer is

。

(8) Synthetic route of A8: essentially the same as a2, except that: monomer is

。

(9) Synthetic route of a 9: essentially the same as a2, except that: monomer is

。

It should be noted that in the synthetic routes of the acrylate adhesives A2-A9, the addition amount of the monomer and the second monomer is only required to ensure that the amount (n) of the substances satisfies the number of repeating units (polymerization degree) in the structural formula; taking a2 as an example, the ratio of the amount of the substance of the monomer to the amount of the second monomer is ensured to be 3: 1, the specific adding quality is not limited herein; the amounts of the initiator and the solvent to be added were calculated as the ratio of the amounts of the monomers, the initiator and the solvent supplied in the synthetic route of A1.

Example 1

(1) Preparing an electrolyte: an electrolyte was obtained by mixing and stirring 16% of ethylene carbonate, 8% of ethyl methyl carbonate, 53.5% of dimethyl carbonate, 1% of vinylene carbonate, 4% of fluoroethylene carbonate, 17% of lithium hexafluorophosphate, and 0.5% of cyano compound B2 in mass%.

(2) Preparing a negative pole piece: mixing 1.8% CMC (carboxymethyl cellulose) with water, stirring to obtain a colloidal solution, sequentially mixing 90.7% graphite and 5% silica material (SiO) ₂ ) Adding 0.5% of conductive agent carbon black and 2% of acrylate binder A1 into the glue solution, mixing and stirring to obtain negative electrode slurry, and performing coating, baking, rolling and slitting to obtain a negative electrode plate;

(3) preparing a positive pole piece: mixing 1.5% PVDF (polyvinylidene fluoride) with water, stirring to obtain a glue solution, and sequentially mixing 96% LiNi _0.8 Co _0.1 Mn _0.1 O ₂ Adding 2.5% of conductive agent carbon black into the glue solution, mixing and stirring to obtain positive electrode slurry, and performing coating, baking, rolling and slitting to obtain a positive electrode piece;

(4) preparing a lithium ion battery: assembling the electrolyte, the negative plate, the diaphragm and the positive plate into a 18650 type cylindrical lithium ion battery; wherein, the liquid injection amount of the battery is 4.8g, and the isolating membrane is a polyethylene ceramic coating composite membrane.

Examples 2 to 9

Essentially the same as example 1, except that:

in examples 2 to 9, the additives were acrylic adhesives A2, A3, A4, A5, A6, A7, A8, and A9, respectively.

Examples 10 to 20

Essentially the same as example 6, except that:

in examples 10 to 20, cyano compounds B1, B3, B4, B5, B6, B7, B8, B9, B10, B11, and B12 were used in an amount of 0.5% respectively.

Examples 21 and 22

Essentially the same as example 6, except that:

in example 21, the cyano compound B2 was used in an amount of 2% and the dimethyl carbonate was used in an amount of 52% by mass;

in example 22, the cyano compound B2 was used in an amount of 5% and the dimethyl carbonate was used in an amount of 49% by mass.

Examples 23 and 24

Essentially the same as example 13, except that:

in example 23, the cyano compound B5 was used in an amount of 1% and the dimethyl carbonate was used in an amount of 53% by mass;

in example 24, cyano compound B5 was used in an amount of 3% and dimethyl carbonate was used in an amount of 51% by mass.

Examples 25 and 26

Essentially the same as example 14, except that:

in example 25, the cyano compound B6 was used in an amount of 1% and the dimethyl carbonate was used in an amount of 53% by mass;

in example 26, cyano compound B6 was used in an amount of 2% and dimethyl carbonate was used in an amount of 52% by mass.

Comparative example 1

Essentially the same as example 1, except that:

the cyano compound B2 and the acrylate adhesive A1 are not added; correspondingly, the mass content of the dimethyl carbonate in the electrolyte is 54 percent; a conventional binder is used in the negative electrode: SBR (styrene butadiene rubber) with the mass content of 2 percent.

Comparative example 2

Essentially the same as in comparative example 1, except that:

SBR is not added; correspondingly, the acrylic ester adhesive A1 is adopted in the negative electrode, and the mass content is 1%; the mass content of the graphite is adaptively adjusted to 91.7%.

Comparative examples 3 and 4

Substantially the same as in comparative example 2, except that:

in comparative example 3, the amount of the acrylic adhesive a1 was 2% and the amount of graphite was 90.7% by mass;

in comparative example 4, the acrylic adhesive a1 was used in an amount of 4% and the graphite was used in an amount of 88.7% by mass.

Comparative example 5

Essentially the same as in comparative example 2, except that: the acrylate adhesive a1 was replaced with the acrylate adhesive a 6.

Comparative example 6

Essentially the same as in comparative example 3, except that: the acrylate adhesive a1 was replaced with the acrylate adhesive a 6.

Comparative example 7

Essentially the same as in comparative example 4, except that: the acrylate adhesive a1 was replaced with the acrylate adhesive a 6.

Comparative example 8

Substantially the same as in comparative example 2, except that: the acrylate adhesive a1 was replaced with the acrylate adhesive A8.

Comparative example 9

Substantially the same as in comparative example 3, except that: the acrylate adhesive a1 was replaced with the acrylate adhesive A8.

Comparative example 10

Essentially the same as in comparative example 4, except that: the acrylate adhesive a1 was replaced with the acrylate adhesive A8.

The sources of the raw materials in the examples and comparative examples described in the present invention are shown below, and the manufacturers and the brands are given below; other reagents or instruments used are not indicated by manufacturers, and are all conventional products which can be obtained by commercial purchase;

CMC: ashland (Ashland), BVH8;

graphite: sequoia sinensis, QCG-X;

carbon black: yirui Stone (IMERYS), Super P-Li;

silicon-oxygen material: sequoia shanghai, AS 3;

PVDF: suwei (SOLVAY), 5130;

diaphragm: shanghai enjie, SV 16; (note: the thickness is 16 μm, the pore size range is 60 nm-100 nm);

SBR: BASF (BASF), 21-11.

Respectively carrying out cycle test and storage test on the lithium ion batteries prepared in the examples 1-26 and the comparative examples 1-10; wherein the content of the first and second substances,

the method for the cycle test comprises the following steps: in a normal temperature environment at 25 ℃, the lithium ion batteries of the examples and the comparative examples are respectively charged to 4.2V at 4C, stood for 5 minutes, discharged to 3V at 20A, stood for 30 minutes, and are charged and discharged in such a cycle manner until the capacity retention rate reaches 70%.

It should be noted that: if the cycle is short-circuited before 70%, recording the number of circles during the short circuit of the cycle; if there was no short circuit at the cycle retention rate of 70%, the number of cycles was recorded.

The storage test method comprises the following steps: in an environment of 60 ℃, taking out the battery at regular intervals until the surface temperature is recovered to normal temperature, testing the alternating current impedance by using an alternating current impedance testing instrument, and judging that the current blocking device in the battery is disconnected if the impedance is infinite; if the AC impedance can be measured, the battery can be judged to be normally conducted.

It should be noted that: when the number of storage days is more than 100 days, the lithium ion battery storage performance is judged to be excellent, and the specific number of days exceeding 100 is not specifically described in the method.

The following cycle test results (unit is circle) of examples 1 to 26 and comparative examples 1 to 10 were in this order: 689 rear short circuit, 753, 723, 845, 897, 876, 862, 835, 821, 789, 864, 859, 876, 835, 831, 819, 803, 847, 822, 851, 847, 802, 824, 782, 805, 766, 400 rear short circuit, 489 rear short circuit, 645 rear short circuit, 512, 636 rear short circuit, 996, 793, 523 rear short circuit, 745, 672.

The following storage test results (in days) were obtained for examples 1 to 26 and comparative examples 1 to 10 in this order: 100+, 70, 50, 30, 60, 50, 40, 50, 70, 80, 70, 100+, 70, 60, 90, 70, 80, 90, 100+, 90, 50, 20, 80, 50, 10.

Fig. 1 shows a comparison of cycle performance of the lithium ion batteries provided in comparative example 1, comparative example 6, and example 14. The abscissa of fig. 1 is the number of cycles, and the ordinate of fig. 1 is the capacity retention rate. Two cells were tested per set and plotted separately, so that there were two curves for each of comparative example 1, comparative example 6, and example 14 in fig. 1.

It can be seen that, after the acrylate adhesive is added in the comparative example 6, the cycle performance is greatly improved, and the short circuit problem does not occur any more, which is mainly related to the restriction of the adhesive on the expansion of the negative pole piece to inhibit the cycle short circuit. After the cyano compound is added in example 14, the cycle capacity retention rate is slightly reduced, mainly related to the loss of polarization capacity caused by the increase of partial impedance, but the better cycle performance can still be maintained.

Meanwhile, fig. 2 shows a comparison graph of coulomb efficiency changes of the three groups of lithium ion batteries during the cycle test; wherein the abscissa of fig. 2 is the number of cycles and the ordinate of fig. 2 is the coulombic efficiency. It was found that the coulomb efficiency of comparative example 1 was greatly reduced after 400 cycles because overcharge was caused by the occurrence of a short circuit inside the battery, the charge capacity was greatly increased, and the coulomb efficiency was rapidly reduced. For another example, the coulombic efficiency of example 14 in fig. 2 is not changed greatly, and the cyclic capacity fading in fig. 1 is also gradually reduced, which indicates that no short circuit occurs inside the battery.

In addition, the invention also provides the change condition of the alternating current impedance in the storage process when the three groups of lithium ion batteries are subjected to the storage test, and the result is shown as follows.

The ac impedance values (impedance unit: m Ω) at 1 st, 3 rd, 5 th, 10 th, 20 th, 30 th, 40 th, 50 th, 60 th, 70 th, 80 th, 90 th, and 100 th days of the three experimental batteries of comparative example 1, comparative example 6, and example 14 (hereinafter referred to as the first battery, the second battery, and the third battery, respectively) were recorded.

It should be noted that the three experimental batteries tested in each group were identical, with the current disconnect device being the earliest time/day of storage in the group. The test was stopped after 100 days, taking into account the resource and time costs.

First cell of comparative example 1: 13.7, 14.11, 13.96, 14.31, 15.16, 15.33, 15.65, 15.71, 15.88, 15.85, 16.04, 16.44;

second cell of comparative example 1: 13.74, 13.99, 14.19, 14.34, 15.18, 15.13, 15.58, 15.79, 15.92, 15.89, 16.14, 16.51;

third cell of comparative example 1: 13.97, 14.15, 14.24, 14.4, 15.04, 15.11, 15.42, 15.55, 15.73, 15.69, 15.88, 16.22.

First cell of comparative example 6: 13.69, 13.82, 14.05, 14.21, 15.03, 15.19, 16.12, then infinity was not measurable;

second cell of comparative example 6: 13.43, 13.76, 13.81, 14.03, 14.92, 15.12, 15.69, 15.77, 15.87, 15.9, then infinity is not measurable;

third cell of comparative example 6: 13.46, 13.8, 13.89, 14.01, 14.71, 14.89, 15.31, 15.58, and then infinity, are not measurable.

First cell of example 14: 13.28, 13.3, 13.49, 13.76, 14.08, 14.32, 14.51, 14.63, 14.78, 14.82, 15.13, 15.19, 15.12;

second cell of example 14: 13.38, 13.31, 14.68, 13.83, 14.04, 14.43, 14.53, 14.65, 14.85, 14.97, 15.07, 15.41, 15.18;

third cell of example 14: 13.35, 13.43, 13.53, 13.87, 14.12, 14.47, 14.55, 14.68, 14.72, 14.94, 15.05, 15.27, 15.19.

From this data result, it can be seen that: the battery of example 14 can be normally conducted after 100 days of high-temperature storage at 60 ℃, while the battery of comparative example 6 cannot be conducted after about 50 days, which shows that the lithium ion battery with only the acrylate binder without the cyano compound additive is more likely to generate a gas side reaction during the high-temperature storage process, and a large amount of gas opens the pressure safety device of the battery, thereby easily limiting the use of the battery.

While particular embodiments of the present invention have been illustrated and described, it will be appreciated that the above embodiments are only intended to illustrate the technical solution of the present invention and not to limit it; those of ordinary skill in the art will understand that: modifications may be made to the above-described embodiments, or equivalents may be substituted for some or all of the features thereof without departing from the spirit and scope of the present invention; the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention; it is therefore intended to cover in the appended claims all such alternatives and modifications that are within the scope of the invention.

Claims

1. A lithium ion battery is characterized by comprising a positive electrode, a negative electrode, electrolyte and a diaphragm; the negative electrode comprises graphite, a silica material and a binder, wherein the binder comprises an acrylate compound; the electrolyte comprises a cyano compound;

the acrylate compound comprises at least one of the following structural formulas A1-A9;

A1、

A2、

A3、

A4、

A5、

A6、

A7、

A8、

A9；

B1、

B2、

B3、

B4、

B5、

B6、

B7、

B8、

B9、

B10、

B11、

B12。

2. the lithium ion battery of claim 1, wherein the lithium ion battery comprises at least one of the following features a and b:

a. in the negative electrode, the mass ratio of the binder to the silica material to the graphite is 0.01-5: 1-99: 0.01 to 98.9;

b. the mass content of the cyano compound in the electrolyte is 0.01-5%.

3. The lithium ion battery of claim 1, wherein the electrolyte comprises a lithium salt, an organic solvent, and the cyano compound;

wherein the lithium salt comprises lithium hexafluorophosphate.

4. The lithium ion battery of claim 3, comprising at least one of the following features A or B:

A. the organic solvent comprises a linear ester and/or a cyclic ester;

the linear ester comprises at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, ethyl propionate, methyl propionate, propyl propionate and methyl acetate; the cyclic ester comprises at least one of ethylene carbonate and propylene carbonate;

wherein the mass content of the linear ester in the electrolyte is 40.00-80.75%; the mass content of the cyclic ester in the electrolyte is 12.00-47.50%;

B. the electrolyte further comprises an additive; the additive comprises at least one of vinylene carbonate, ethylene carbonate, fluoro carbonate, 1, 3-propane sultone, 1, 3-propene sultone, 2, 4-butane sultone, methylene methane disulfonate, lithium difluoro oxalate borate, lithium dioxalate borate, lithium tetrafluoroborate, lithium bis fluoro sulfonyl imide, lithium bis trifluoro methane sulfonyl imide and lithium difluoro phosphate.

5. The lithium-ion battery of claim 1, wherein the positive electrode comprises a ternary material; the structural formula of the ternary material is LiNi _x Co _y Mn _z O ₂ Wherein x + y + z = 1.

6. The lithium ion battery of claim 1, wherein the separator comprises a porous polymer film having a pore size of 500 nm or less;

the porous polymer film includes at least one of polyethylene, polypropylene, a ceramic-coated membrane, an aramid-coated membrane, and a polyethylene-polypropylene composite membrane.

7. The method for preparing the lithium ion battery according to any one of claims 1 to 6, comprising the steps of:

assembling the anode, the cathode and the diaphragm, injecting electrolyte, and packaging to obtain the lithium ion battery;

the preparation method of the electrolyte comprises the following steps: fully mixing components forming the electrolyte to obtain the electrolyte;

the preparation method of the negative electrode comprises the following steps: fully mixing graphite, a silica material and a binder to obtain a negative electrode slurry, and coating and performing high-temperature treatment to obtain the negative electrode;

the preparation method of the positive electrode comprises the following steps: and fully mixing the positive electrode material and the binder to obtain positive electrode slurry, and coating and performing high-temperature treatment to obtain the positive electrode.