A crosslinking agent, a polymer binder for lithium ion batteries, and a preparation method and application thereof

Abstract

The application discloses a crosslinking agent, a polymer binder for a lithium ion battery and a preparation method and application thereof. The crosslinking agent is an amino-terminated polyether compound, and the amino-terminated polyether compound comprises a compound with a structural formula as shown in formula I and / or formula II: a polymer binder for a lithium ion battery and a preparation method and application thereof. The ether bond of the amino-terminated polyether provided by the application can provide a three-dimensional channel for the movement of Li + , and higher Li + diffusion kinetics can be achieved. In addition, the preparation process of the crosslinking agent is simple to operate, and the electrode preparation cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries. More particularly, it relates to a crosslinking agent, a polymer binder for lithium ion batteries and a preparation method and application thereof. BACKGROUND

[0002] With the increasing demand for long endurance and fast charging capability of electric vehicles and 3C electronic products, the development of high energy density lithium ion batteries (LIBs) has become an urgent need. Among various strategies, developing high-capacity electrode materials is the most effective way to improve the energy density of batteries. In particular, silicon anodes have a high theoretical capacity of 4200 mA·h·g -1 , which is 10 times higher than that of the commercially used graphite anode (372 mA·h·g -1 ). Obviously, replacing the graphite anode with the silicon anode can significantly improve the energy density of lithium ion batteries. In addition, silicon materials have the advantages of low cost, abundant reserves, environmental protection, etc., and are ideal anode materials. However, the rapid capacity decay caused by the large volume change (~ 400%) during repeated lithiation and delithiation seriously hinders its practical application in commercial lithium ion batteries. The huge volume change of the silicon anode leads to the pulverization of the electrode material, the continuous growth of the solid-electrolyte interface (SEI), the loss of electronic contact, and the shedding of the electrode material from the current collector, resulting in poor cycle performance.

[0003] In order to solve the above problems, researchers have developed a series of innovative strategies, including reducing the size of Si, preparing Si / C composite materials, constructing effective coatings, and using new binders. Among various methods, using new binders to stabilize the silicon anode has attracted more and more attention due to its simplicity and effectiveness. As a key component of the electrode, the binder plays a crucial role in bonding the active material with the conductive additive together and firmly adhering to the current collector. Many studies have been devoted to the development of high-performance binders, including polymers with rich polar groups (such as alginate, polyacrylic acid (PAA)), self-healing polymers, cross-linked polymers, and conductive polymers. Among various binders, conductive polymer binders have attracted great interest. However, these conductive polymer binders can only improve the electrochemical performance of nano-sized silicon anodes. For micro-sized silicon anodes with the advantages of low cost and high energy density, the low mechanical properties of the conductive polymer binder cannot maintain the stability of the electrode structure, resulting in poor cycle stability, and therefore there is still a rapid capacity decay ability.

[0004] Therefore, the present application provides a crosslinking agent, a polymer binder for lithium ion batteries and a preparation method and application thereof to at least solve one of the above problems. SUMMARY

[0005] A first object of the present application is to provide a crosslinking agent.

[0006] A second object of the present application is to provide a preparation method of the crosslinking agent.

[0007] A third object of the present application is to provide an application of the crosslinking agent.

[0008] A fourth object of the present application is to provide a polymer binder for lithium ion batteries.

[0009] A fifth object of the present application is to provide a preparation method of the polymer binder for lithium ion batteries.

[0010] A sixth object of the present application is to provide an application of the polymer binder for lithium ion batteries.

[0011] To achieve the above objects, the present application adopts the following technical solutions:

[0012] The present application provides a crosslinking agent, which is an end-amino polyether compound, and the end-amino polyether compound comprises a compound with a structural formula as shown in Formula I and / or Formula II:

[0013]

[0014] Formula I; Formula II.

[0015] The ether bond (C-O-C) in the end-amino polyether compound of the crosslinking agent provided by the present application can provide three-dimensional channels for the movement of Li + , and can realize higher Li + diffusion kinetics; in addition, the preparation process of the crosslinking agent is simple to operate, and the consumption cost is reduced.

[0016] The present application further provides a preparation method of the crosslinking agent, comprising the following steps:

[0017] The polyacid is mixed with ether amine / polyether amine, and the crosslinking agent is obtained after acylation, extraction, and rotary evaporation.

[0018] The ether amine / polyether amine has rich terminal amino groups, and can realize high crosslinking degree with the polyacid.

[0019] Preferably, the molar mass of the ether amine / polyether amine is greater than the molar mass of the polyacid.

[0020] Preferably, the molar ratio of the polyacid to the ether amine / polyether amine is 1:1.5-3.0.

[0021] Preferably, the polyacid is one or more of a monoacid, a diacid, and a triacid.

[0022] Preferably, the polyacid comprises the following mass percentages of raw materials:

[0023] Monobasic acid, 4 wt%;

[0024] Dibasic acid, 80 wt%; and

[0025] Tribasic acid, 16 wt%.

[0026] Preferably, the monobasic acid is a fatty acid with one carboxyl group, the dibasic acid is an aromatic acid with two carboxyl groups, and the tribasic acid is an aromatic acid with three carboxyl groups.

[0027] Preferably, the monobasic acid has a structure as shown in Formula III:

[0028]

[0029] Formula III.

[0030] Preferably, the dibasic acid has a structure as shown in Formula IV:

[0031]

[0032] Formula IV.

[0033] Preferably, the tribasic acid has a structure as shown in Formula V:

[0034]

[0035] Formula V.

[0036] Preferably, the polyacid is polyfatty acid Empol 1016.

[0037] Preferably, the ether amine is one or both of ethylene glycol bis(2-aminoethy)ether and diethylene glycol bis(3-aminopropyl)ether.

[0038] Preferably, the polyether amine is one or more of PEA-D230, PEA-D400, and PEA-D2000.

[0039] Preferably, the acylation reaction conditions are: stirring the reaction under inert gas protection at a temperature of 140-160℃ for 12-24h; further, a large number of experiments of the application have proved that the acylation reaction temperature can be 140-145℃, 140-150℃, 140-155℃, 150-155℃, 150-160℃, 155-160℃, etc.; wherein the results obtained at 160℃ are optimal; below 140℃, the reaction is incomplete, and above 160℃, a higher heating medium is required, increasing the preparation cost. The acylation reaction time can be 12-15h, 12-18h, 12-20h, 15-18h, 15-20h, 15-24h, 18-20h, 18-24h, etc., wherein the results obtained at 24h are optimal; below 12h, the reaction is incomplete, and above 24h, the reaction period is too long.

[0040] Preferably, the inert gas is argon.

[0041] Preferably, the extraction is to dissolve the product obtained by the acylation reaction in a mixed solvent of chloroform and deionized water after cooling to room temperature, and standing for 8-12h. Further, a large number of experiments of the application have proved that the standing time for extraction can be 8-9h, 8-10h, 8-11h, 9-10h, 9-11h, 9-12h, 10-11h, 10-12h, 11-12h, etc., wherein the results obtained at 12h are optimal; below 8h, the extraction is incomplete, the product yield is low, and above 12h, the product preparation period is increased.

[0042] Preferably, the volume ratio of chloroform to deionized water is 1:1-10.

[0043] Preferably, the extraction is to dissolve the product obtained by the acylation reaction in a mixed solvent of chloroform and deionized water after cooling to room temperature, and standing for 8-12h. Further, a large number of experiments of the application have proved that the standing time for extraction can be 8-9h, 8-10h, 8-11h, 9-10h, 9-11h, 9-12h, 10-11h, 10-12h, 11-12h, etc., wherein the results obtained at 12h are optimal; below 8h, the extraction is incomplete, the product yield is low, and above 12h, the product preparation period is increased.

[0042] Preferably, the volume ratio of chloroform to deionized water is 1:1-10.

[0043] Preferably, the extraction is at least three times in succession to ensure that the ether amine not participating in the reaction is fully removed.

[0044] Preferably, the rotary evaporation of the extracted product is at 100-120℃; further, a large number of experiments of the application have proved that the rotary evaporation temperature can be 100℃, 110℃, 120℃; wherein the results obtained at 100℃ are optimal; below 100℃, the product cannot be evaporated dry, and above 120℃, the energy consumption is too high.

[0045] The application further provides a use of a crosslinking agent in the preparation of a polymer binder for lithium ion batteries.

[0046] The application further provides a polymer binder for lithium ion batteries, prepared from the aforementioned crosslinking agent, which comprises a compound with a structural formula as shown in Formula VI and / or Formula VII:

[0047]

[0048] Formula VI; Formula VII.

[0049] The polymer binder structure provided by the present application has amide bonds and ether bonds, the formation of the strong covalent bond of the amide bond successfully constructs a 3D cross-linking network, effectively buffers the stress impact generated when the silicon volume expands, the ether bond (C-O-C) provides a three-dimensional channel for the rapid diffusion of lithium ions, accelerates the transport of Li + , and thus the high energy density of the micron silicon negative electrode can be realized under a large current density.

[0050] The present application further provides a preparation method of a polymer binder for a lithium ion battery, comprising the following steps:

[0051] (1) mixing the aforementioned cross-linking agent and polyacrylic acid and then dissolving them in an organic solvent to obtain a mixture;

[0052] (2) drying the mixture to obtain the polymer binder for a lithium ion battery.

[0053] Preferably, the organic solvent in step (1) is N-methyl pyrrolidone.

[0054] Preferably, the mass ratio of the polyacrylic acid to the cross-linking agent in step (1) is 7:3~9:1. Further, a large number of experiments of the present application prove that the mass ratio of the polyacrylic acid to the cross-linking agent can be 7:3~4:1, 4:1~9:1, etc., wherein the result is optimal when the mass ratio is 4:1; the cross-linking network of the product prepared when the mass ratio is lower than 7:3 has lower strength, and the cross-linking network of the product prepared when the mass ratio is higher than 9:1 has lower toughness

[0055] Preferably, the drying in step (2) is vacuum drying at 150~180℃ for 2~3h. Further, a large number of experiments of the present application prove that the drying temperature in step (2) can be 150~160℃, 150~170℃, 160~170℃, 160~180℃, 170~180℃, etc., wherein the result is optimal when the drying temperature is 150℃, the organic solvent in the polymer is not dried sufficiently when the temperature is lower than 150℃, and the polymer structure changes when the temperature is higher than 180℃; the result is optimal when the drying time in step (2) is 3h, the drying is insufficient when the time is lower than 2h, and the product drying period is too long when the time is higher than 3h, increasing energy consumption.

[0056] The present application further provides an application of the polymer binder for a lithium ion battery in the preparation of a lithium ion battery negative material.

[0057] The present application further provides a lithium ion battery negative material prepared from the aforementioned polymer binder for a lithium ion battery.

[0058] The present application further provides a preparation method of the lithium ion battery negative electrode material prepared from the aforementioned polymer binder for lithium ion batteries.

[0059] Preferably, the preparation method of the lithium ion battery negative electrode material prepared from the polymer binder for lithium ion batteries comprises the following steps:

[0060] (i) mixing the aforementioned polymer binder for lithium ion batteries and water to obtain a polymer binder solution;

[0061] (ii) mixing the polymer binder solution with carbon nanotubes, and drying to obtain the lithium ion battery negative electrode material.

[0062] Preferably, the concentration of the polymer binder solution in step (i) is 10-50 mg·mL -1 . More preferably, the concentration of the polymer binder solution in step (i) is 30 mg·mL -1 .

[0063] Preferably, the carbon nanotubes in step (i) are long single-walled carbon nanotubes or long multi-walled carbon nanotubes.

[0064] Preferably, the mass ratio of the carbon nanotubes to the polymer binder in step (ii) is 0.1-1:1. More preferably, the mass ratio of the carbon nanotubes to the polymer binder in step (ii) is 1:1

[0065] Preferably, the drying in step (ii) is vacuum drying at 150-180℃ for 2-3h. Further, a large number of experiments of the present application have confirmed that the drying temperature in step (ii) can be 150-160℃, 150-170℃, 160-170℃, 160-180℃, 170-180℃, etc., wherein the results obtained when the drying temperature is 150℃ are optimal, and when the temperature is lower than 150℃, the organic solvent in the electrode is not removed sufficiently, and when the temperature is higher than 180℃, the polymer structure will change; when the drying time in step (ii) is 3h, the results obtained are optimal, and when the time is lower than 2h, the electrode is not dried sufficiently, and when the time is higher than 3h, the electrode drying period is too long, increasing the energy consumption.

[0066] The present application further provides a lithium ion battery negative electrode prepared from the aforementioned polymer binder for lithium ion batteries.

[0067] The present application further provides a preparation method of the lithium ion battery negative electrode prepared from the aforementioned polymer binder for lithium ion batteries.

[0068] Preferably, the preparation method of the lithium ion battery anode prepared from the polymer binder for lithium ion batteries comprises the following steps:

[0069] Step one, mixing the aforementioned polymer binder for lithium ion batteries and water to obtain a polymer binder solution;

[0070] Step two, mixing micron silicon, the polymer binder solution and carbon nanotubes, coating on a copper foil, and drying to obtain a lithium ion battery anode.

[0071] The present application synthesizes a new three-dimensional network with high electronic conductivity and high ionic conductivity by means of the high conductivity of carbon nanotubes, the ether bond in the terminal amino polyether, and the amidation reaction of the terminal amino group and polyacrylic acid. At the same time, the introduction of the ether bond soft chain in the terminal amino polyether promotes the transport of lithium ions and enhances the flexibility of the binder, better adapts to the volume expansion of silicon particles under high load, and improves the electrochemical performance.

[0072] Preferably, the concentration of the polymer binder solution in step one is 10-50 mg·mL -1 . More preferably, the concentration of the polymer binder solution in step one is 30 mg·mL -1 .

[0073] Preferably, the mass ratio of micron silicon, the polymer binder solution and carbon nanotubes in step two is 8:1:1.

[0074] Preferably, the particle size of the micron silicon in step two is 1-10 μm, and the average particle size is 2.38 μm.

[0075] Preferably, the drying in step two is vacuum drying at 150-180℃ for 2-3h.

[0076] The present application further provides a lithium ion battery prepared from the aforementioned lithium ion battery anode.

[0077] The lithium ion battery anode material prepared by the present application has excellent mechanical properties. A new three-dimensional composite network is introduced to solve the problems of low electronic and ionic conductivity of micron silicon-based anodes. This design can provide high electronic conductivity by means of single-walled carbon nanotubes and high ionic conductivity by means of the ether bond in the terminal amino polyether. At the same time, chemical cross-linking increases the cross-linking degree and improves the tensile properties. Combined with the strong composite network with high electronic and ionic conductivity, this new three-dimensional composite network has excellent mechanical properties, so that the prepared lithium ion battery anode has the highest load, hardness, modulus, high tensile property and elastic recovery when the indentation depth is ~1000 nm.

[0078] Unless otherwise indicated, any range of any of the numerical parameters set forth herein includes all the intermediate values and all the ranges between the indicated end values and any of the intermediate values, as well as any ranges that can be formed of any of the intermediate values, or the end values, or any of the intermediate values and the end values.

[0079] The beneficial effects of the present application are as follows:

[0080] (1) The ether bond (C-O-C) of the crosslinking agent terminal amino polyether provided by the present application can provide three-dimensional channels for the movement of Li + , and can realize higher Li + diffusion kinetics; in addition, the preparation process of the crosslinking agent is simple to operate, and reduces the electrode preparation cost.

[0081] (2) The polymer binder for lithium ion batteries provided by the present application has an amide bond and an ether bond, the formation of the strong covalent bond of the amide bond successfully constructs a 3D crosslinking network, effectively buffers the stress impact generated when the silicon volume expands, and the ether bond (C-O-C) provides three-dimensional channels for the rapid diffusion of lithium ions, accelerates the transport of Li + , and thus the high energy density of the lithium ion battery anode can be realized under high current density.

[0082] (3) The present application utilizes the reaction between the amino group of the terminal amino polyether and the carboxyl group of the polyacrylic acid to prepare a lithium ion battery anode material in the presence of carbon nanotubes, which couples the high strength of the polyacrylic acid and the high toughness and high lithium ion conductivity of the ether bond soft chain of the terminal amino polyether, has excellent mechanical, electrochemical properties and energy dissipation capacity, is a new type of three-dimensional composite network with high electronic and ionic conductivity, so that the prepared lithium ion battery silicon anode still has excellent cycle stability under high load, and a high energy density lithium ion battery can be prepared. BRIEF DESCRIPTION OF DRAWINGS

[0083] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0084] Figure 1 The infrared spectra of the polymer binder (PAA-ATPE), polyacrylic acid (PAA), terminal amino polyether (ATPE), and the mixture of terminal amino polyether and polyacrylic acid (PAA&ATPE) in Example 20 are shown.

[0085] Figure 2 The high-resolution C element XPS spectrum of ATPE in Example 1 is shown.

[0086] Figure 3 The high-resolution C element XPS spectrum of PAA-ATPE in Example 20 is shown.

[0087] Figure 4A graphical representation showing the high solubility of PAA-ATPE, PAA, and ATPE in water in Example 20.

[0088] Figure 5 A graphical representation showing the tensile stress-strain curve results of PAA-ATPE and PAA in Example 20.

[0089] Figure 6 A graphical representation showing the load-displacement curve of the lithium-ion battery anode prepared in Example 32 and Comparative Example 2.

[0090] Figure 7 A graphical representation showing the modulus and hardness of the lithium-ion battery anode prepared in Example 32 and Comparative Example 2 calculated from the load-displacement curve.

[0091] Figure 8 A graphical representation showing the force-displacement curve of the 180° peel test of the lithium-ion battery anode prepared in Example 32 and Comparative Example 2.

[0092] Figure 9 A graphical representation showing the average peel strength of the lithium-ion battery anode prepared in Example 32 and Comparative Example 2.

[0093] Figure 10 A graphical representation showing the first charge-discharge curve and the corresponding first coulombic efficiency of the lithium-ion battery anode prepared in Example 32 at 100 mA·g -1

[0094] Figure 11 A graphical representation showing the first charge-discharge curve and the corresponding first coulombic efficiency of the lithium-ion battery anode prepared in Comparative Example 2 at 100 mA·g -1

[0095] Figure 12 A graphical representation showing the long cycle performance of the lithium-ion battery anode of µSi / PAA-ATPE, µSi / PAA-9-ATPE, and µSi / PAA-7-ATPE prepared in Example 32, Example 37, and Example 38, respectively, at 2 A·g -1

[0096] Figure 13 A graphical representation showing the long cycle performance of the lithium-ion battery anode of µSi / PAA prepared in Comparative Example 2 at 2 A·g -1

[0097] Figure 14 A graphical representation showing the cycle performance of the lithium-ion battery anode of µSi / PAA-ATPE prepared in Example 32 at different Si loadings.

[0098] Figure 15 ​​​​The infrared fitting spectrum of ethylene glycol bis (2-aminoethyl) ether (BAE), the polymer binder (PAA-BAE) in Comparative Example 1 is shown. DETAILED DESCRIPTION

[0099] In order to more clearly illustrate the present application, the present application is further described below in conjunction with preferred embodiments and the accompanying drawings. Like components are denoted by the same reference numerals in the drawings. It should be understood by those skilled in the art that the specific descriptions below are illustrative rather than limiting, and should not limit the scope of protection of the present application.

[0100] In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specified.

[0101] In the present application, the preparation method is a conventional method unless otherwise specified. The raw materials used are available from public commercial channels unless otherwise specified. The percentages are mass percentages unless otherwise specified.

[0102] Example 1

[0103] The present embodiment provides a preparation method of a crosslinking agent, comprising the following steps:

[0104] 100 g of polyacid (polyacid is poly fatty acid Empol 1016) and 57 g of ethylene glycol bis (2-aminoethyl) ether are weighed and mixed, and an acylation reaction is carried out at 160°C for 24 h under argon protection; the acylation reaction product is cooled, dissolved in chloroform and deionized water in a volume ratio of 1:1, and left to stand for 12 h for extraction, and the extraction is carried out three times in succession; then the liquid obtained by extraction is rotary evaporated at 100°C to obtain a crosslinking agent terminal amino polyether (ATPE). The structure characterization of ATPE is shown in the infrared spectrum in Figure 1 and the X-ray photoelectron spectroscopy technology in Figure 2 The ATPE obtained in the present embodiment has the highest yield, and the optimal yield is 92%.

[0105] Examples 2-5

[0106] The present embodiment provides a preparation method of a crosslinking agent, and the steps are the same as those in Example 1, except that the acylation reaction temperature is 140°C, 145°C, 150°C and 155°C, respectively.

[0107] Examples 6-9

[0108] The present embodiment provides a preparation method of a crosslinking agent, and the steps are the same as those in Example 1, except that the acylation reaction time is 12 h, 15 h, 18 h and 20 h, respectively.

[0109] Examples 10-13

[0110] The embodiment provides a preparation method of a crosslinking agent, and steps are same to those in the embodiment 1, and the only difference is that the standing time during extraction is 8h, 9h, 11h and 11h respectively.

[0111] Embodiments 14-15

[0112] The embodiment provides a preparation method of a crosslinking agent, and steps are same to those in the embodiment 1, and the only difference is that the liquid obtained by extraction is rotary evaporated at 110 DEG C and 120 DEG C respectively.

[0113] Embodiments 16-19

[0114] The embodiment provides a preparation method of a crosslinking agent, and steps are same to those in the embodiment 1, and the only difference is that the ethylene glycol bis (2-aminoethyl) ether is replaced by diethylene glycol bis (3-aminopropyl) ether, PEA-D230, PEA-D400 and PEA-D2000 respectively.

[0115] Embodiment 20

[0116] The embodiment provides a preparation method of a polymer binder for a lithium ion battery, and the method comprises the following steps:

[0117] (1) mixing polyacrylic acid (PAA) and the crosslinking agent terminal amino polyether prepared in the embodiment 1 according to a mass ratio of 8:2 (named as PAA&ATPE), and then dissolving the mixture in N-methyl pyrrolidone to obtain a clear light yellow solution after stirring;

[0118] (2) placing the light yellow solution prepared in the step (1) in a vacuum dryer at 150 DEG C for 3h to obtain a polymer binder (PAA-ATPE).

[0119] The structure characterization of the PAA-ATPE can be seen from infrared spectrograms in the Figure 1 and X-ray photoelectron spectroscopy technology in the Figure 3 Compared with the physical mixing and the PAA&ATPE (structure characterization can be seen from infrared spectrograms in the Figure 1 ) which is not crosslinked, the PAA-ATPE reacted at high temperature presents obvious chemical bonds. Compared with the reactants PAA and ATPE dissolved in water, the PAA-ATPE after crosslinking is not dissolved in water (see Figure 4 ), which proves that the crosslinking reaction occurs between the PAA and the ATPE. Compared with the embodiments 21-26, the PAA-ATPE prepared in the embodiment has the most excellent comprehensive mechanical property, that is, high strength is maintained while high toughness is realized.

[0120] Embodiments 21-22

[0121] The embodiment provides a preparation method of a polymer binder for a lithium ion battery, and the specific steps are the same as those in Embodiment 20, except that the mass ratio of polyacrylic acid and crosslinking agent terminal amino polyether in step (1) is 9:1, 7:3 respectively.

[0122] Embodiments 23-25

[0123] The embodiment provides a preparation method of a polymer binder for a lithium ion battery, and the specific steps are the same as those in Embodiment 20, except that the temperature of vacuum drying in step (2) is 160 DEG C, 170 DEG C, 180 DEG C respectively.

[0124] Embodiment 26

[0125] The embodiment provides a preparation method of a polymer binder for a lithium ion battery, and the specific steps are the same as those in Embodiment 20, except that the time of vacuum drying in step (2) is 2h.

[0126] Embodiment 27

[0127] The embodiment provides a preparation method of a lithium ion battery negative material, comprising the following steps:

[0128] (i) mixing the polymer binder prepared in Embodiment 20 with water to prepare a polymer binder solution with a concentration of 30 mg·mL-1; -1

[0129] (ii) mixing the polymer binder solution with single-walled carbon nanotubes (CNT) at a mass ratio of 1:1, and vacuum drying at 150 DEG C for 3h to prepare a lithium ion battery negative material (PAA-ATPE / CNT).

[0130] The application finds that, in the presence of CNT, a new three-dimensional composite polymer network with high electronic and ionic conductivity is formed between ATPE and PAA through an amide reaction; thanks to the high electronic conductivity of CNT, the ether bond group of ATPE has good Li + conductivity, and the 3D chemically bonded polymer network (PAA-ATPE) has a high tensile property of 560% (see Figure 5 ), the prepared PAA-ATPE / CNT network has the tough performance of high ionic and high electronic conductivity, so that it becomes an advanced conductive network for realizing stable operation of a silicon particle negative electrode.

[0131] Embodiments 28-30

[0132] The embodiment provides a preparation method of a lithium ion battery negative material, and the specific steps are the same as those in Embodiment 27, except that the temperature of vacuum drying in step (ii) is 160 DEG C, 170 DEG C, 180 DEG C respectively.​

[0133] Example 31

[0134] This example provides a method for preparing a lithium ion battery anode material, the specific steps are the same as Example 27, the only difference is that the vacuum drying time in step (ii) is 2h.

[0135] Example 32

[0136] This example provides a method for preparing a lithium ion battery anode, comprising the following steps:

[0137] Step one, mix the polymer binder prepared in Example 20 with water to prepare a 30 mg·mL -1 of polymer binder solution;

[0138] Step two, using slurry coating process, mix micron silicon powder, polymer binder solution and CNT uniformly according to the mass ratio of 8:1:1 and coat on copper foil, vacuum drying at 150℃ for 3h, to prepare lithium ion battery anode (µSi / PAA-ATPE).

[0139] Compared with the lithium ion battery anode (µSi / PAA) prepared in Comparative Example 2, µSi / PAA-ATPE electrode shows higher hardness and modulus (see Figure 6 and Figure 7 ), higher peel strength (see Figure 8 and Figure 9 ). In addition, compared with µSi / PAA, µSi / PAA-ATPE electrode also shows higher initial discharge capacity and first cycle coulombic efficiency (see Figure 10 and Figure 11 ), better cycle stability (see Figure 12 and Figure 13 ). More importantly, µSi / PAA-ATPE also shows excellent cycle stability under high active material loading conditions (see Figure 14 ).

[0140] The lithium ion battery anode electrode prepared in this example has a high capacity of 3789.0 mAh·g -1 under the condition of 100 mA·g -1 , and the initial coulombic efficiency (ICE) is as high as 92.2%; under the condition of 2 A·g -1 , it has good cycle stability, and the capacity retention rate is as high as 92.0%. It shows excellent cycle performance; under high Si loading, after 50 cycles at a current density of 0.6 A·g -1 , it still has a capacity retention rate as high as 71.6%.

[0141] Examples 33-35

[0142] This example provides a preparation of a lithium ion battery anode. The specific steps are the same as those of Example 32, except that in Step 2, the temperature of vacuum drying is 160°C, 170°C, and 180°C, respectively.

[0143] Example 36

[0144] This example provides a preparation of a lithium ion battery anode. The specific steps are the same as those of Example 32, except that in Step 2, the time of vacuum drying is 2h.

[0145] Example 37

[0146] This example provides a preparation of a lithium ion battery anode. The specific steps are the same as those of Example 32, except that in Step 1, the polymer binder prepared in Example 20 is replaced by the polymer binder prepared in Example 21, and the final lithium ion battery anode is named as µSi / PAA-9-ATPE.

[0147] The µSi / PAA-ATPE electrode prepared in Example 32 has a better cycle performance than the µSi / PAA-9-ATPE electrode prepared in this example (see Figure 12 ).

[0148] Example 38

[0149] This example provides a preparation of a lithium ion battery anode. The specific steps are the same as those of Example 32, except that in Step 1, the polymer binder prepared in Example 20 is replaced by the polymer binder prepared in Example 22, and the final lithium ion battery anode is named as µSi / PAA-7-ATPE.

[0150] The µSi / PAA-ATPE electrode prepared in Example 32 has a better cycle performance than the µSi / PAA-7-ATPE electrode prepared in this example (see Figure 12 ).

[0151] Comparative Example 1

[0152] This comparative example provides a preparation method of a polymer binder, comprising the following steps:

[0153] (1) Mix ethyleneglycol bis(2-aminoethy)ether (BAE) and polyacrylic acid in a mass ratio of 2:8, dissolve in N-methylpyrrolidone, stir to obtain a clear light yellow solution;

[0154] (2) Place the solution prepared in step (1) in a vacuum dryer at 150°C for 3h to obtain a polymer binder PAA-BAE.

[0155] Compared with Example 20, the same quality BAE of the present comparative example contains more terminal amino groups and has a higher degree of chemical cross-linking with polyacrylic acid, so the toughness of the polymer binder PAA-BAE is poorer than that of PAA-APTE in Example 20. The structural characterization of PAA-BAE is shown in the infrared spectrum (Fig. 2). Figure 15 ).

[0156] Comparative Example 2

[0157] The present comparative example provides a preparation method of a lithium ion battery negative electrode, comprising the following steps:

[0158] (1) 2.0 g of polyacrylic acid is weighed and dissolved in N-methyl pyrrolidone to obtain a clear solution, and the PAA and water are mixed to prepare a 30 mg mL -1 PAA solution;

[0159] (2) Using a slurry coating process, micron silicon powder, PAA solution and CNT are mixed uniformly at a mass ratio of 8:1:1 and coated on a copper foil, and vacuum dried at 150°C for 3h to prepare a lithium ion battery negative electrode (μSi / PAA).

[0160] Compared with Example 32, the binder used in the present comparative example is a pure PAA linear binder, which cannot effectively alleviate the volume expansion of the silicon negative electrode, and has poor lithium ion conductivity.

[0161] Obviously, the above examples of the present application are only examples for clearly illustrating the present application, and are not a limitation on the embodiments of the present application. For ordinary skilled in the art, on the basis of the above description, other different forms of changes or variations can also be made, and it is impossible to enumerate all the embodiments here. Any changes or variations that belong to the technical solutions of the present application and are derived from the obvious changes or variations are still within the protection scope of the present application.

Claims

1. A crosslinking agent, characterized by, The cross-linking agent is an amino-terminated polyether compound, which includes a compound with a structural formula as shown in Formula I and / or Formula II: Formula I; Formula II.

2. A method for producing the crosslinking agent as claimed in claim 1, characterized by, The method comprises the following steps: The polyacid is mixed with an ether amine, acylated, extracted, and rotary evaporated to obtain the cross-linking agent; The ether amine is ethylene glycol bis(2-aminoethyl) ether; The polyacid includes diacids and triacids; the diacids have a structural formula as shown in Formula IV: Formula IV; The triacids have a structural formula as shown in Formula V: Formula V.

3. The method for preparing the crosslinking agent according to claim 2, characterized in that, The polyacid also includes monoacids; the monoacids have a structural formula as shown in Formula III: Formula III.

4. The method for preparing a crosslinking agent according to claim 2, characterized by, The acylation reaction is performed under inert gas protection at a temperature of 140-160°C for 12-24 hours.

5. The method for preparing the crosslinking agent according to claim 2, characterized in that, The extraction is performed by dissolving the product obtained from the acylation reaction in a mixed solvent of chloroform and deionized water after cooling, and standing for 8-12 hours.

6. The method for preparing the crosslinking agent according to claim 2, characterized in that, The rotary evaporation is performed on the product obtained from the extraction at 100-120°C.

7. The method for preparing the crosslinking agent according to claim 2, characterized in that, The molar mass of the ether amine is greater than that of the polyacid.

8. The method for preparing the crosslinking agent according to claim 2, characterized in that, The molar ratio of the polyacid to the ether amine is 1:1.5-3.

0.

9. The method for preparing the crosslinking agent according to claim 3, characterized in that, The polyacid includes raw materials with the following mass percentages: Monoacids, 4 wt%; Diacids, 80 wt%; and Triacids, 16 wt%.

10. A polymer binder for lithium ion batteries, characterized in that, The polymer binder for lithium ion batteries is prepared from the cross-linking agent of claim 1, and includes a compound with a structural formula as shown in Formula VI and / or Formula VII: Formula VI; Formula VII.

11. A method of preparing a polymer binder for lithium ion batteries as claimed in claim 10, characterized in that, The method comprises the following steps: (1) mixing the cross-linking agent of claim 1 and polyacrylic acid, and dissolving in an organic solvent to obtain a mixture; (2) drying the mixture to obtain the polymer binder for lithium ion batteries.

12. The method of claim 11, wherein the polymer binder is prepared by the steps of: a) dissolving a polymer in a solvent; b) adding a lithium salt to the solution; and c) removing the solvent from the solution to form the polymer binder. The organic solvent in step (1) is N-methyl pyrrolidone.

13. The method of claim 11, wherein the polymer binder is prepared by the steps of: a) dissolving a polymer in a solvent; b) adding a lithium salt to the solution; and c) removing the solvent from the solution to form the polymer binder. The mass ratio of the polyacrylic acid to the cross-linking agent in step (1) is 7:3-9:

1.

14. The method of claim 11, wherein the polymer binder is prepared by the steps of: a) dissolving a polymer in a solvent; b) adding a lithium salt to the solution; and c) removing the solvent from the solution to form the polymer binder. The drying in step (2) is vacuum drying at 150-180°C for 2-3 hours.

15. A lithium ion battery anode material prepared from the polymer binder for lithium ion batteries of claim 10.

16. A method for preparing a lithium ion battery anode material prepared from the polymer binder of claim 15, characterized in that, The method comprises the following steps: (i) mixing the polymer binder for lithium ion batteries of claim 10 and water to obtain a polymer binder solution; (ii) mixing the polymer binder solution and carbon nanotubes, and drying to obtain the lithium ion battery anode material.

17. The method of claim 16, wherein the lithium-ion battery anode material is prepared from the polymer binder. The concentration of the polymer binder solution in step (i) is 10-50 mg mL -1 .

18. The method of claim 16, wherein the lithium-ion battery anode material is prepared from the polymer binder. The mass ratio of the carbon nanotubes to the polymer binder in step (ii) is 0.1-1:

1.

19. The method of claim 16, wherein the lithium-ion battery anode material is prepared from the polymer binder. The drying in step (ii) is vacuum drying at 150-180°C for 2-3 hours.

20. A lithium ion battery anode prepared from the polymer binder for lithium ion batteries of claim 10.

21. A method of producing a lithium ion battery anode prepared from the polymer binder of claim 20, wherein, The method comprises the following steps: Step one, mixing the polymer binder for lithium ion batteries of claim 10 and water to obtain a polymer binder solution; Step two, mixing micron silicon, the polymer binder solution, and carbon nanotubes, coating on a copper foil, and drying to obtain the lithium ion battery anode.

22. The method of claim 21, wherein the lithium-ion battery anode is prepared from the polymer binder. The mass ratio of the micron silicon, the polymer binder solution, and the carbon nanotubes in step two is 8:1:

1.

23. The method of claim 21, wherein the lithium-ion battery anode is prepared from a polymer binder. The drying in step two is vacuum drying at 150-180°C for 2-3h.

24. A lithium ion battery prepared from a lithium ion battery anode prepared from the polymer binder for lithium ion batteries according to claim 20.

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