Negative electrode adhesive and preparation method thereof, battery negative electrode and lithium battery

Abstract

The present invention discloses a negative electrode binder, a preparation method thereof, a battery negative electrode, and a lithium battery. The negative electrode binder is prepared from gelatin, a small molecule crosslinking agent, and a copolymer monomer via a free radical copolymerization method. The chemical crosslinking between the gelatin and the copolymer in the negative electrode binder gives the three-dimensional network binder a very high molecular weight, providing strong adhesion and tightly bonding the silicon negative electrode to the current collector. Furthermore, the dynamic hydrogen bonds formed between the abundant amino, hydroxyl, and carbonyl groups on the gelatin and copolymer molecular chains ensure that the binder recovers within the instant of hydrogen bond breakage during charge and discharge, thereby effectively adapting to the significant volume changes of the active material silicon, tightly bonding the silicon negative electrode and the conductive agent to the current collector, preventing slurry shedding and further extending the battery's cycle life.

Description

Technical Field

[0001] The present invention relates to the field of lithium batteries, and in particular to a negative electrode adhesive and a preparation method thereof, a battery negative electrode and a lithium battery. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in the field of new energy vehicles. With the development of the new energy vehicle industry, people have put forward higher requirements for the performance of lithium-ion batteries, especially energy density, cycle life and safety.

[0003] To achieve high-energy-density battery design and performance goals, lithium-ion battery chemistries containing silicon anodes are almost inevitable. Silicon-based anode materials offer high specific capacity, but they experience significant and repeated volume expansion and contraction during charge and discharge, leading to poor electrode stability, cracking of the electrode, pulverization of the active material, particle fragmentation, and the continuous formation of a SEI film. This significantly degrades battery cycle performance, creating a critical issue that needs to be addressed.

[0004] The patent with publication number CN107681158A provides a double cross-linked self-healing adhesive, comprising a polysaccharide polymer containing a polar group or a synthetic polymer containing a polar group and metal ions, preferably polyacrylic acid (PAA) and Fe 3+ ions. The binder not only contains the network structure constructed by PAA itself through esterification cross-linking, but also Fe 3+ Secondary crosslinking is achieved through ionic interaction with PAA and Fe 3+ Inducing PAA to form a self-healing hydrogel system can achieve double cross-linking of silicon negative electrode materials, which can repair the mechanical damage of the electrode during the charge and discharge cycle, thereby improving the cycle performance of silicon-based negative electrode materials.

[0005] However, the self-healing double cross-linked network in the above patent comes from PAA itself through esterification cross-linking and Fe 3+ The ionic interaction with PAA is realized, and Fe 3+ Introduced into the negative electrode binder, Fe 3+ Ion migration may occur during the charge and discharge process, affecting the self-repair effect. 3+ Cross-linking will make PAA gel brittle and affect the mechanical properties of PAA itself. Summary of the Invention

[0006] The purpose of the present invention is to provide a negative electrode adhesive and a preparation method thereof, a battery negative electrode and a lithium battery, so as to solve the problems in the prior art of poor electrode stability and cracking of the electrode sheet caused by the huge and repeated volume expansion and contraction of the negative electrode material during the charging and discharging process.

[0007] To achieve the above object, a method for preparing a negative electrode binder comprises:

[0008] providing an aqueous gelatin solution;

[0009] adding a small molecule cross-linking agent to a gelatin aqueous solution and stirring to obtain a precursor solution;

[0010] Providing a copolymer solution and an aqueous ammonium persulfate solution, mixing the copolymer solution with the aqueous ammonium persulfate solution, and then adding the mixture to the precursor solution to obtain a mixed solution;

[0011] The mixed solution is allowed to undergo free radical polymerization reaction under vacuum conditions, and then stirred at room temperature to obtain a negative electrode binder.

[0012] In one embodiment of the present invention, the step of providing an aqueous gelatin solution comprises:

[0013] Add gelatin to deionized water and disperse evenly;

[0014] The pH was adjusted to alkaline to obtain a gelatin aqueous solution.

[0015] In one embodiment of the present invention, the step of adjusting the pH to alkaline to obtain a gelatin aqueous solution comprises:

[0016] The pH is adjusted to 10-11 to obtain a gelatin aqueous solution.

[0017] In one embodiment of the present invention, the step of providing an aqueous gelatin solution comprises:

[0018] Add gelatin to deionized water and disperse evenly;

[0019] After adjusting the pH to alkaline and performing hydrolysis treatment, the supernatant was collected after centrifugation;

[0020] The supernatant is dialyzed, and the retained solution is taken and freeze-dried to obtain hydrolyzed gelatin, which is then added to deionized water to obtain a gelatin aqueous solution.

[0021] In one embodiment of the present invention, the hydrolysis temperature is 70°C-90°C, the hydrolysis time is 20-40 minutes, and the mass ratio of the small molecule crosslinker to the hydrolyzed gelatin is (0.01-0.05):1. It is best to continuously stir during the hydrolysis process, and the stirring reaction time is preferably 10-12 hours.

[0022] In one embodiment of the present invention, the molecular weight cut-off of the dialysis bag used in the dialysis treatment is 10,000 to 14,000; and the dialysis treatment time is 48 hours to 72 hours.

[0023] In one embodiment of the present invention, the step of providing the copolymer solution and the ammonium persulfate aqueous solution comprises:

[0024] The copolymer monomer is added into deionized water and mixed uniformly to obtain a copolymer solution; the mass ratio of the copolymer monomer to the hydrolyzed gelatin is (6-8):1; the volume ratio of the ammonium persulfate aqueous solution to the precursor solution is (0.18-0.4):(6-10).

[0025] In one embodiment of the present invention, the copolymer monomer is selected from at least one of acrylamide and N-isopropylacrylamide.

[0026] In one embodiment of the present invention, the step of causing the mixed solution to undergo free radical polymerization under vacuum conditions and then stirring at room temperature comprises:

[0027] The mixed solution is subjected to vacuum exhaust treatment, and then a promoter is added to stir the solution at room temperature; the promoter is N,N,N'N'-tetramethylethylenediamine; and the stirring reaction time is 2h-5h.

[0028] In one embodiment of the present invention, the concentration of the gelatin aqueous solution is 5 wt%-10 wt%.

[0029] An embodiment of the present invention further provides a negative electrode binder, which is prepared using the above-mentioned preparation method.

[0030] An embodiment of the present invention further provides a battery negative electrode, comprising a current collector and a negative electrode material attached to a surface of the current collector, wherein the negative electrode material comprises a silicon material and the negative electrode binder as described above.

[0031] An embodiment of the present invention further provides a lithium battery, comprising the battery negative electrode as described above.

[0032] This embodiment provides a negative electrode adhesive and its preparation method, a battery negative electrode, and a lithium battery. The negative electrode adhesive is prepared from gelatin, a small molecule crosslinking agent, and a copolymer monomer by a free radical copolymerization method. The beneficial effects include at least: 1. The chemical crosslinking between the gelatin and the copolymer makes the three-dimensional network adhesive have a very high molecular weight, which can provide strong bonding force and tightly bond the silicon negative electrode to the current collector; 2. The dynamic hydrogen bonds formed between the abundant amino, hydroxyl, and carbonyl groups on the gelatin and copolymer molecular chains can ensure that the adhesive recovers within the instant of hydrogen bond breakage during the charge and discharge process, thereby being able to well adapt to the huge volume change of the active material silicon, tightly bonding the silicon negative electrode and the conductive agent to the current collector, preventing the slurry from falling off, and further extending the cycle life of the battery. DETAILED DESCRIPTION

[0033] The "ranges" disclosed herein are in the form of lower limits and upper limits. These can be one or more lower limits, and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges that can be defined in this manner are inclusive and combinable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present invention, unless otherwise specified, all embodiments and preferred embodiments described herein can be combined to form new technical solutions.

[0034] In the present invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0035] In the present invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially.

[0036] The following describes various embodiments of the negative electrode binder and its preparation method, battery negative electrode and lithium battery of the present invention.

[0037] Example 1

[0038] The preparation method of the negative electrode binder comprises the following steps:

[0039] (1) 10 g of gelatin was dispersed in water and magnetically stirred at 600 rpm for 5 h to obtain a uniform aqueous solution having a mass fraction of 10 wt %. In other embodiments, the mass fraction of the aqueous solution can be selected between 5 wt % and 10 wt %.

[0040] (2) A 10 wt% sodium hydroxide aqueous solution is added to the aqueous solution obtained in step (1), and the pH of the aqueous solution is adjusted to alkaline. In this embodiment, the pH of the aqueous solution is 10.0, thereby obtaining a pH-adjusted aqueous solution. The purpose of adjusting the pH of the aqueous solution to alkaline is to increase the solubility of gelatin. In a preferred embodiment of the present invention, the pH of the aqueous solution can be between 10 and 11.

[0041] In a preferred embodiment of the present invention, the pH value of the aqueous solution obtained in step (1) may not be adjusted, and the aqueous solution obtained in step (1) may be directly subjected to the hydrolysis treatment in step (3), and then sequentially subjected to steps (4), (5), (6), (7), (8), (9), and (10) to obtain the negative electrode binder.

[0042] (3) The aqueous solution after pH adjustment in step (2) is heated to 70° C., stirred and hydrolyzed for 40 minutes, cooled to room temperature, and then stirred and reacted for 10 hours to obtain a hydrolyzed solution. In a preferred embodiment of the present invention, the hydrolysis temperature can be 70-90° C., the hydrolysis time is 20-40 minutes, and the stirring reaction time is 10-12 hours.

[0043] (4) The hydrolysis solution obtained in step (3) was centrifuged at a speed of 8000 r / min for 10 minutes, and the supernatant was collected. The supernatant was the hydrolyzed protein solution.

[0044] (5) The upper layer of the hydrolyzed protein solution obtained in step (4) is dialyzed for 48 hours using a dialysis bag with a molecular weight cutoff of 10,000, and then freeze-dried for 36 hours. The retained solution is taken and freeze-dried to obtain hydrolyzed gelatin. In other embodiments, the molecular weight cutoff of the dialysis bag used for the dialysis treatment can be 10,000-14,000, and the dialysis treatment time can also be adjusted between 48 hours and 72 hours.

[0045] (6) 0.5 g of the hydrolyzed gelatin obtained in step (5) was added to deionized water and magnetically stirred at 600 rpm for 20 minutes to obtain a uniform gelatin aqueous solution with a concentration of 5 wt%.

[0046] (7) Add 0.003 g of methacrylic anhydride to the gelatin aqueous solution obtained in step (6), stir for 3 minutes until it is fully dissolved, and then stir and react at room temperature for 10 hours to obtain a precursor aqueous solution that can undergo addition polymerization reaction.

[0047] Methacrylic anhydride acts as a small molecule crosslinker, reacting with gelatin to form double bonds in the gelatin, which participate in the free radical polymerization reaction. The specific reaction formula is as follows:

[0048]

[0049] In a preferred embodiment of the present invention, the small molecule crosslinking agent can be methacrylic anhydride and / or crotonic anhydride. Preferably, the mass ratio of the small molecule crosslinking agent to the hydrolyzed gelatin is (0.01-0.05):1; and the stirring reaction time is 10-12 hours.

[0050] In a preferred embodiment of the present invention, methacrylic anhydride can also be directly added to the aqueous solution after adjusting the pH in step (2) to obtain a precursor aqueous solution, and then step (8), step (9) and step (10) are performed, wherein the precursor aqueous solution added in step (7) is the precursor aqueous solution obtained by directly adding methacrylic anhydride to the aqueous solution after adjusting the pH in step (2). In this way, the negative electrode binder required by the present invention can also be prepared.

[0051] (8) 1.8 g of N-isopropylacrylamide was added to water and stirred for 3 minutes to obtain a fully dissolved copolymer solution having a concentration of 2.6 wt %. In other embodiments, the concentration of N-isopropylacrylamide can be selected between 2 wt % and 3 wt %. The copolymer solution may also include acrylamide and / or N-isopropylacrylamide.

[0052] (9) 0.18 mL of a 2.5 wt% ammonium persulfate (APS) aqueous solution was added to the copolymer solution of step (8), and stirred for 3 min until it was fully dissolved. Then, 6 mL of the precursor aqueous solution of step (7) that can continue the addition polymerization reaction was added and stirred thoroughly to obtain a mixed solution.

[0053] (10) After the mixed solution obtained in step (9) was evacuated for 5 minutes, 0.18 mL of a 2.5 wt% aqueous solution of N,N,N',N'-tetramethylethylenediamine (TEMED) was added thereto, and the mixture was stirred for 2 hours to allow the double-bonded gelatin to undergo a free radical polymerization reaction with N-isopropylacrylamide to obtain a negative electrode binder. The N,N,N',N'-tetramethylethylenediamine was added to the mixed solution as a accelerator to ensure that the double-bonded gelatin in the mixed solution and N-isopropylacrylamide in the mixed solution undergo a free radical polymerization reaction at room temperature.

[0054] The reaction formula for the free radical polymerization of double-bonded gelatin and N-isopropylacrylamide is as follows:

[0055]

[0056] In a preferred embodiment of the present invention, the volume ratio of the accelerator N,N,N',N'-tetramethylethylenediamine to the precursor solution in step (7) is (0.18-0.4):(6-10).

[0057] Example 2

[0058] In this embodiment, the preparation method of the negative electrode binder includes the following steps:

[0059] (1) 10 g of gelatin was dispersed in water and magnetically stirred at 600 rpm for 10 h to obtain a uniform aqueous solution having a mass fraction of 5 wt %. In other embodiments, the mass fraction of the aqueous solution can be selected between 5 wt % and 10 wt %.

[0060] (2) A 10 wt% sodium hydroxide aqueous solution is added to the aqueous solution obtained in step (1), and the pH of the aqueous solution is adjusted to alkaline. In this embodiment, the pH of the aqueous solution is 11.0, thereby obtaining an aqueous solution after adjusting the pH. The purpose of adjusting the pH of the aqueous solution to alkaline is to increase the solubility of gelatin. In a preferred embodiment of the present invention, the pH of the aqueous solution can be 10 to 11.

[0061] In a preferred embodiment of the present invention, the pH value of the aqueous solution obtained in step (1) may not be adjusted, and the aqueous solution obtained in step (1) may be directly hydrolyzed and then sequentially subjected to steps (4), (5), (6), (7), (8), (9), and (10) to obtain the negative electrode binder.

[0062] (3) The aqueous solution after pH adjustment in step (2) is heated to 80° C., stirred and hydrolyzed for 30 minutes, cooled to room temperature, and then stirred and reacted for 12 hours to obtain a hydrolyzed solution. In a preferred embodiment of the present invention, the hydrolysis temperature can be 70-90° C., the hydrolysis time is 20-40 minutes, and the stirring reaction time is 10-12 hours.

[0063] (4) The hydrolysis solution obtained in step (3) was centrifuged at a speed of 8000 r / min for 10 minutes, and the supernatant was collected. The supernatant was the hydrolyzed protein solution.

[0064] (5) The upper layer of the hydrolyzed protein solution obtained in step (4) is dialyzed for 48 hours using a dialysis bag with a molecular weight cutoff of 14,000, and then freeze-dried for 36 hours. The retained solution is taken and freeze-dried to obtain hydrolyzed gelatin. In other embodiments, the molecular weight cutoff of the dialysis bag used for the dialysis treatment can be 10,000-14,000, and the dialysis treatment time can also be adjusted between 48 hours and 72 hours.

[0065] (6) 0.5 g of the hydrolyzed gelatin obtained in step (5) was added to deionized water and magnetically stirred at 600 rpm for 25 minutes to obtain a uniform gelatin aqueous solution with a concentration of 5 wt%.

[0066] (7) Add 0.0038 g of methacrylic anhydride to the gelatin aqueous solution obtained in step (6), stir for 4 min until it is fully dissolved, and then stir and react at room temperature for 12 h to obtain a precursor aqueous solution that can undergo addition polymerization reaction.

[0067] Methacrylic anhydride acts as a small molecule crosslinker, reacting with gelatin to form double bonds in the gelatin, which participate in the free radical polymerization reaction. The specific reaction formula is as follows:

[0068]

[0069] In a preferred embodiment of the present invention, the small molecule crosslinking agent can be methacrylic anhydride and / or crotonic anhydride. Preferably, the mass ratio of the small molecule crosslinking agent to the hydrolyzed gelatin is (0.01-0.05):1; and the stirring reaction time is 10-12 hours.

[0070] In a preferred embodiment of the present invention, methacrylic anhydride may be directly added to the aqueous solution after adjusting the pH in step (2), and then the negative electrode binder is obtained through steps (8), (9) and (8).

[0071] (8) 2.5 g of N-isopropylacrylamide was added to water and stirred for 3 minutes to obtain a fully dissolved copolymer solution having a concentration of 2.6 wt %. In other embodiments, the concentration of N-isopropylacrylamide can be selected between 2 wt % and 3 wt %. The copolymer solution may also include acrylamide and / or N-isopropylacrylamide.

[0072] (9) 0.25 mL of a 2.5 wt% aqueous solution of ammonium persulfate (APS) was added to the copolymer solution of step (8), and stirred for 3 min until it was fully dissolved. Then, 8 mL of the precursor aqueous solution of step (7) that can continue the addition polymerization reaction was added and stirred thoroughly to obtain a mixed solution.

[0073] (10) After the mixed solution obtained in step (9) was evacuated for 7 minutes, 0.25 mL of a 2.5 wt% aqueous solution of N,N,N',N'-tetramethylethylenediamine (TEMED) was added thereto, and the mixture was stirred for 4 hours to allow the double-bonded gelatin to undergo a free radical polymerization reaction with N-isopropylacrylamide to obtain a negative electrode binder. The N,N,N',N'-tetramethylethylenediamine was added to the mixed solution as a accelerator to ensure that the double-bonded gelatin in the mixed solution and N-isopropylacrylamide in the mixed solution undergo a free radical polymerization reaction at room temperature.

[0074] The reaction formula for the free radical polymerization of double-bonded gelatin and N-isopropylacrylamide is as follows:

[0075]

[0076] In a preferred embodiment of the present invention, the volume ratio of the accelerator N,N,N',N'-tetramethylethylenediamine to the precursor solution in step (7) is (0.18-0.4):(6-10).

[0077] The present invention also provides a negative electrode adhesive, which is prepared using the above-mentioned preparation method.

[0078] The present invention also provides a battery negative electrode, comprising a current collector and a negative electrode material attached to the surface of the current collector, wherein the negative electrode material comprises a silicon material and the negative electrode adhesive as described above.

[0079] The present invention also provides a lithium battery comprising the battery negative electrode as described above.

[0080] The present invention discloses a negative electrode binder, a preparation method thereof, a battery negative electrode, and a lithium battery. The negative electrode binder is prepared from gelatin, a small molecule crosslinking agent, and a copolymer monomer via a free radical copolymerization method. The chemical crosslinking between the gelatin and the copolymer in the negative electrode binder gives the three-dimensional network binder a very high molecular weight, providing strong adhesion and tightly bonding the silicon negative electrode to the current collector. Furthermore, the dynamic hydrogen bonds formed between the abundant amino, hydroxyl, and carbonyl groups on the gelatin and copolymer molecular chains ensure that the binder recovers within the instant of hydrogen bond breakage during charge and discharge, thereby effectively adapting to the significant volume changes of the active material silicon, tightly bonding the silicon negative electrode and the conductive agent to the current collector, preventing slurry shedding and further extending the battery's cycle life.

[0081] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the scope of the patent application of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing a negative electrode binder, wherein the negative electrode binder is used for a silicon-containing negative electrode, characterized in that: include: providing an aqueous gelatin solution; adding a small molecule cross-linking agent to the gelatin aqueous solution and stirring to obtain a precursor solution; Providing a copolymer solution and an aqueous ammonium persulfate solution, mixing the copolymer solution with the aqueous ammonium persulfate solution, and then adding the mixture to the precursor solution to obtain a mixed solution; allowing the mixed solution to undergo a free radical polymerization reaction under vacuum conditions, and then stirring at room temperature to obtain a negative electrode binder; Wherein, the step of providing gelatin aqueous solution comprises: Add gelatin to deionized water and disperse evenly; After adjusting the pH to alkaline and performing hydrolysis treatment, the supernatant was collected after centrifugation; The supernatant is dialyzed, and the retained solution is taken and freeze-dried to obtain hydrolyzed gelatin, which is then added to deionized water to obtain the gelatin aqueous solution.

2. The preparation method according to claim 1, wherein Adjusting the pH to alkaline includes adjusting the pH to 10-11.

3. The preparation method according to claim 1, wherein The temperature of the hydrolysis treatment is 70° C.-90° C., and the time of the hydrolysis treatment is 20 min-40 min. The mass ratio of the small molecule cross-linking agent to the hydrolyzed gelatin is (0.01-0.05):

1.

4. The preparation method according to claim 1, wherein The molecular weight cut-off of the dialysis bag used in the dialysis treatment is 10,000-14,000; and the time of the dialysis treatment is 48 hours-72 hours.

5. The preparation method according to claim 1, wherein The step of providing a copolymer solution and an ammonium persulfate aqueous solution includes: adding copolymer monomers to deionized water and mixing them uniformly to obtain a copolymer solution; the mass ratio of the copolymer monomers to the hydrolyzed gelatin is (6-8):1; and the volume ratio of the ammonium persulfate aqueous solution to the precursor solution is (0.18-0.4):(6-10).

6. The preparation method according to claim 5, wherein The copolymer monomer is selected from at least one of acrylamide and N-isopropylacrylamide.

7. The preparation method according to claim 1, wherein The steps of causing the mixed solution to undergo free radical polymerization under vacuum conditions and then stirring at room temperature include: The mixed liquid is subjected to a vacuum exhaust treatment, and a promoter is added to stir the mixed liquid at room temperature; the promoter is N,N,N'N'-tetramethylethylenediamine; and the stirring reaction time is 2 hours to 5 hours.

8. The preparation method according to claim 1, wherein The concentration of the gelatin aqueous solution is 5wt%-10wt%.

9. A negative electrode binder, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. A battery negative electrode, comprising a current collector and a negative electrode material attached to the surface of the current collector, characterized in that: The negative electrode material includes a silicon material and the negative electrode binder according to claim 9. A lithium battery comprising the battery negative electrode according to claim 10 .

Images