A kind of lithium battery aqueous negative electrode emulsion and preparation method thereof

Abstract

The present invention relates to the technical field of battery binders, and in particular to a lithium battery aqueous negative electrode emulsion and a preparation method thereof. The lithium battery aqueous negative electrode emulsion comprises the following components by weight: 100 parts of pre-emulsion; 5-10 parts of phosphoric acid functional monomers containing divinyl; 2-4 parts of neutralizer; 0.2-0.4 parts of initiator; and 60 parts of water. The lithium battery aqueous negative electrode emulsion provided by the present invention improves crosslinking and molecular weight after polymerization by introducing phosphoric acid functional monomers containing divinyl. The lithium battery aqueous negative electrode emulsion binder can form a crosslinked network structure with a higher degree of polymerization after film formation, tightly grasps the graphite surface, inhibits the rebound of graphite at full charge, and improves the high temperature cycle performance of lithium ion batteries.

Description

Technical Field

[0001] The invention relates to the technical field of battery binders, and in particular to an aqueous negative electrode emulsion for a lithium battery and a preparation method thereof. Background Art

[0002] Although the negative electrode binder accounts for a small proportion of the lithium battery electrode, the electrochemical performance of lithium-ion batteries is closely related to the negative electrode binder, so the negative electrode binder plays an important role in lithium batteries. The main function of the negative electrode binder is to ensure that the active material particles and the active particles and the current collector have a certain bonding strength during the charge and discharge process of the battery, and it is also conducive to the formation of the SEI film. Since lithium ions will be embedded and de-embedded in the active material during the charge and discharge process, causing the volume of the active material to expand or shrink, the negative electrode binder must also have a certain flexibility and rigidity to adapt to this volume change.

[0003] The research and development of negative electrode binders is moving towards improving battery performance, achieving green manufacturing processes, and adapting to new electrode materials. As consumers have increasingly higher requirements for the performance of lithium-ion batteries, the innovation and improvement of binders will be one of the key areas for the development of lithium-ion battery technology.

[0004] Currently, the commonly used negative electrode binders are butadiene-styrene emulsion (SBR), styrene acrylic emulsion, polyacrylic acid solution (PAA), etc. Among them, although styrene acrylic emulsion has good kinetics and excellent low DCR, its disadvantages such as poor high-temperature cycle performance and large full-charge rebound limit the application of styrene acrylic emulsion in lithium-ion power and energy storage batteries. Summary of the invention

[0005] In order to solve the problem that styrene acrylic emulsion in the prior art has poor high temperature cycle performance and large full charge rebound when used for lithium ion batteries, the present invention provides a lithium battery aqueous negative electrode emulsion, which introduces a divinyl-containing phosphoric acid functional monomer to increase crosslinking points, so that the resin can form a network crosslinking structure, improve the high temperature cycle capacity retention rate of the lithium ion battery, introduce phosphate groups, increase the adhesion of the graphite layer on the negative electrode current collector, further improve the battery high temperature cycle capacity retention rate and reduce full charge rebound. The lithium battery aqueous negative electrode emulsion synthesized by the present invention can be directly used in power and energy storage batteries and has a lower DCR.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A lithium battery aqueous negative electrode emulsion, comprising the following components in parts by weight:

[0008] Pre-emulsion 100 parts;

[0009] 5-10 parts of a divinyl-containing phosphoric acid functional monomer;

[0010] 2-4 parts of neutralizer;

[0011] Initiator 0.2-0.4 parts;

[0012] 60 parts of water.

[0013] Optionally, the pre-emulsion comprises the following components in parts by weight:

[0014] Styrene 20-50 parts;

[0015] 30-60 parts of oil-soluble acrylic monomer;

[0016] 5-10 parts of water-soluble monomer;

[0017] 2-5 parts of cross-linking monomer;

[0018] Anionic emulsifier 0.5-2 parts;

[0019] Nonionic emulsifier 0.2-1 part;

[0020] 40 parts of water.

[0021] Optionally, the divinyl-containing phosphoric acid functional monomer is prepared according to the following method:

[0022] Pentaerythritol phosphate, glycidyl methacrylate, a polymerization inhibitor and a solvent are mixed, deoxygenated, and then heated to 130-140° C. for a ring-opening reaction to obtain the divinyl-containing phosphoric acid functional monomer.

[0023] Optionally, the molar ratio of the pentaerythritol phosphate to the glycidyl methacrylate is 1:(1-3).

[0024] Optionally, the oil-soluble acrylic ester monomer is selected from at least one of butyl acrylate, isooctyl acrylate, butyl methacrylate, methyl methacrylate, isobornyl methacrylate and octadecyl acrylate.

[0025] Optionally, the water-soluble monomer is selected from at least one of acrylic acid, methacrylic acid, itaconic acid, hydroxyethyl acrylate and hydroxyethyl methacrylate.

[0026] Optionally, the cross-linking monomer is selected from at least one of acrylamide, acryloylmorpholine, hydroxyethyl acrylamide, butylated acrylamide, diacetone acrylamide and silicone monomers.

[0027] Optionally, the anionic emulsifier is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium dodecyl diphenyl ether disulfonate, and sodium dioctyl sulfosuccinate.

[0028] Optionally, the nonionic emulsifier is selected from at least one of fatty alcohol polyoxyethylene ether, Tween 80, and alkyl alcohol polyether.

[0029] Another object of the present invention is to provide a method for preparing the aqueous negative electrode emulsion for lithium batteries as described above, comprising the following steps:

[0030] S1: Dissolve anionic emulsifier and nonionic emulsifier in water according to the formula, add styrene, oil-soluble acrylic ester monomer, water-soluble monomer and cross-linking monomer, stir to obtain a pre-emulsion;

[0031] S2: according to the formula, water and part of the pre-emulsion are mixed, and part of the initiator is added and stirred to obtain a first reaction solution;

[0032] S3: raising the temperature of the first reaction liquid to 82-84° C., stirring at a constant temperature to carry out polymerization reaction, to obtain a second reaction liquid;

[0033] S4: adding the remaining pre-emulsion, the remaining initiator and the divinyl-containing phosphate functional monomer to the second reaction liquid for reaction. After the reaction is completed, cooling to 50° C., adding a neutralizer, adjusting the pH to 6-8, stirring, and then lowering the temperature to 40-45° C., filtering, and obtaining a lithium battery aqueous negative electrode emulsion.

[0034] The beneficial effects of the present invention are:

[0035] The aqueous negative electrode emulsion for lithium batteries provided by the present invention increases the molecular weight by introducing a phosphoric acid functional monomer containing divinyl, and after the molecular weight is increased, the binder can form a cross-linked network structure with a higher degree of polymerization, tightly grasp the graphite surface, and suppress the rebound of the graphite when fully charged, and the phosphate radical increases the adhesion of the graphite on the current collector. The cross-linking and adhesion are improved, and the high-temperature cycle capacity retention rate of the lithium-ion battery is greatly improved. DETAILED DESCRIPTION

[0036] The present invention is now further described in detail. The embodiments described below are exemplary and intended to be used to explain the present invention, but cannot be understood as limiting the present invention. All other embodiments obtained by ordinary technicians in this field without creative work based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0037] When existing styrene acrylic emulsions are used in lithium-ion batteries, in addition to poor high temperature resistance, they also have disadvantages such as large electrode rebound when fully charged, which limits the application field of styrene acrylic emulsions.

[0038] In order to solve the problem that the styrene acrylic emulsion in the prior art has poor high temperature resistant cycle performance when used in lithium ion batteries, the present invention provides a lithium battery aqueous negative electrode emulsion, which comprises the following components in parts by weight:

[0039] Pre-emulsion 100 parts;

[0040] 5-10 parts of a divinyl-containing phosphoric acid functional monomer;

[0041] 2-4 parts of neutralizer;

[0042] Initiator 0.2-0.4 parts;

[0043] 60 parts of water.

[0044] The high temperature cycle performance of lithium-ion batteries and the effect of full-charge rebound of the pole piece are directly related to the stripping force of the negative electrode binder on the current collector and the coating strength of the graphite. The present invention introduces a divinyl-containing phosphoric acid functional monomer into the aqueous negative electrode emulsion of the lithium battery, which can increase the crosslinking points by using the divinyl group, and can make the resin form a network crosslinking structure. The aqueous negative electrode emulsion of lithium batteries synthesized using the functional monomer has high stripping force, which improves the high temperature cycle of the battery; it has a network crosslinking structure, covers the graphite, has a strong cohesive force, and helps to suppress the volume change of graphite during charging and discharging; at the same time, the aqueous negative electrode emulsion of lithium batteries has good dynamic performance, can realize fast charging of lithium-ion batteries, and suppress volume expansion during fast charging.

[0045] The aqueous negative electrode emulsion for lithium batteries provided by the present invention improves crosslinking and increases molecular weight after polymerization by introducing a divinyl-containing phosphate functional monomer. The aqueous negative electrode emulsion binder for lithium batteries can form a crosslinked network structure with a higher degree of polymerization after film formation, tightly grasps the graphite surface, inhibits the rebound of the graphite when fully charged, and improves the high-temperature cycle performance of the lithium-ion battery.

[0046] In order to ensure the high temperature resistance of the aqueous negative electrode emulsion of the lithium battery, the preferred pre-emulsion of the present invention comprises the following components in parts by weight:

[0047] Styrene 20-50 parts;

[0048] 30-60 parts of oil-soluble acrylic monomer;

[0049] 5-10 parts of water-soluble monomer;

[0050] 2-5 parts of cross-linking monomer;

[0051] Anionic emulsifier 0.5-2 parts;

[0052] Nonionic emulsifier 0.2-1 part;

[0053] 40 parts of water.

[0054] Further, the present invention preferably contains divinyl phosphoric acid functional monomers prepared according to the following method:

[0055] Pentaerythritol phosphate, glycidyl methacrylate, polymerization inhibitor and solvent are mixed, deoxygenated, preferably deoxygenated with nitrogen for 30 minutes, heated to 130-140° C. for ring-opening reaction, preferably for 6-8 hours, and cooled to obtain a slightly yellow liquid, which is the target product, that is, a divinyl-containing phosphoric acid functional monomer.

[0056] In the present invention, the polymerization inhibitor in the preparation process of the functional monomer is preferably selected from at least one of hydroquinone, p-hydroxyanisole, methylhydroquinone, and 2,6-di-tert-butyl-p-cresol; and the solvent is preferably selected from at least one of isophorone, diethylene glycol butyl ether, diacetone alcohol, ethylene glycol butyl ether, and dipropylene glycol methyl ether.

[0057] Since the solvents used in the preparation process of the divinyl-containing phosphoric acid functional monomer are all solvents that are miscible with water, it is not necessary to remove the solvent after the preparation is completed.

[0058] The divinyl-containing phosphoric acid functional monomer prepared by the present invention may have two structures, as shown in the following formula:

[0059] ;

[0060] .

[0061] The above two structures are both target products.

[0062] The divinyl-containing phosphoric acid functional monomer prepared by the present invention, in addition to containing divinyl bonds, also has abundant phosphate groups, hydroxyl groups and flexible segments, all of which help to improve the adhesion of the binder on the negative electrode collector, thereby further improving the high-temperature cycle performance of the lithium-ion battery.

[0063] In order to take into account both the stripping force and economy of the aqueous negative electrode emulsion binder for lithium batteries, the molar ratio of pentaerythritol phosphate to glycidyl methacrylate in the preferred preparation process of the present invention is 1: (1-3).

[0064] In order to ensure the stripping force of the aqueous negative electrode emulsion of the lithium battery, the present invention preferably selects at least one of the neutralizing agent selected from ammonia water, sodium hydroxide, lithium hydroxide, calcium hydroxide and triethanolamine; preferably selects at least one of the initiator selected from ammonium persulfate, potassium persulfate and azobisisobutylamidine hydrochloride; preferably selects at least one of the oil-soluble acrylic ester monomer selected from butyl acrylate, isooctyl acrylate, butyl methacrylate, methyl methacrylate, isobornyl methacrylate and octadecyl acrylate; preferably selects at least one of the water-soluble monomer selected from acrylic acid, methacrylic acid, itaconic acid, hydroxyethyl acrylate and hydroxyethyl methacrylate; preferably selects at least one of the cross-linking monomer selected from acrylamide, acryloyl morpholine, hydroxyethyl acrylamide, butyl ether acrylamide, diacetone acrylamide and silicone monomer; preferably selects at least one of the anionic emulsifier selected from sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium dodecyl diphenyl ether disulfonate and sodium sulfonated dioctyl succinate; preferably selects at least one of the nonionic emulsifier selected from fatty alcohol polyoxyethylene ether, Tween 80 and alkyl alcohol polyether.

[0065] The existing styrene acrylic emulsion has poor high-temperature cyclability and large electrode rebound when fully charged, which limits its application field and is mostly used in the field of digital 3C batteries. The lithium battery aqueous negative electrode emulsion provided by the present invention has a peeling force that is 60% higher than that of competing products on the market, and reduces the electrode rebound by 40% when fully charged, which solves the shortcomings of lithium battery aqueous negative electrode emulsion in power batteries and can be used in power batteries.

[0066] Another object of the present invention is to provide a method for preparing the aqueous negative electrode emulsion for lithium batteries as described above, the preparation method comprising the following steps:

[0067] S1: Dissolve anionic emulsifier and nonionic emulsifier in water according to the formula, add styrene, oil-soluble acrylic ester monomer, water-soluble monomer and cross-linking monomer, stir to obtain a pre-emulsion;

[0068] S2: according to the formula, water and part of the pre-emulsion (preferably 5%-10% of the mass of the pre-emulsion) are mixed, and then part of the initiator (preferably 25% of the mass of the initiator) is added, and stirred to obtain a first reaction liquid;

[0069] S3: raising the temperature of the first reaction liquid to 82-84° C., stirring at a constant temperature to carry out polymerization reaction, preferably for 0.5-1 h, to obtain a second reaction liquid;

[0070] S4: Add the remaining pre-emulsion, the remaining initiator and the divinyl-containing phosphoric acid functional monomer to the second reaction liquid for reaction. After the reaction is completed, cool to 50°C, add a neutralizer, adjust the pH to 6-8, stir, and then reduce the temperature to 40-45°C, filter, and obtain a lithium battery aqueous negative electrode emulsion; preferably, in this step, continuously add the remaining pre-emulsion and the remaining initiator while stirring, and the dropwise addition time is 3-4h. When the pre-emulsion has 20% weight remaining, add the divinyl-containing phosphoric acid functional monomer, stir for 5-10min, and then continue to drop the remaining pre-emulsion and the remaining initiator, and the dropwise addition time is 1h. After the dropwise addition is completed, keep the temperature constant for 2-3h. After the reaction is completed, cool to 50°C, add a neutralizer to the reaction system, adjust the solution pH to 6-8, stir for 30min, reduce the temperature of the reaction system to 40-45°C, and filter with a 300-mesh filter to obtain a lithium battery aqueous negative electrode emulsion with a solid content of 40-50%.

[0071] The method for preparing a water-based negative electrode emulsion for a lithium battery provided by the present invention has a simple process. The prepared water-based negative electrode emulsion for a lithium battery has improved crosslinking and increased molecular weight after polymerization by introducing a phosphoric acid functional monomer containing divinyl groups. The binder for the water-based negative electrode emulsion for a lithium battery can form a cross-linked network structure with a higher degree of polymerization after film formation, tightly grasp the surface of graphite, inhibit the rebound of graphite when fully charged, and improve the high-temperature cycle performance of the lithium ion battery. In addition, in the preparation process, the phosphoric acid functional monomer containing divinyl groups is added later, so that functional groups such as phosphate ester and hydroxyl groups can be grafted on the surface of the binder, which helps to make the binder for the water-based negative electrode emulsion for a lithium battery have higher peeling force.

[0072] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below.

[0073] Unless otherwise specified, the divinyl-containing phosphoric acid functional monomers in the embodiments and comparative examples of the present invention are prepared according to the following method:

[0074] 456 g (1 mole) of pentaerythritol phosphate, 284 g (2 moles) of glycidyl methacrylate, 0.14 g (0.5 ten thousandths) of inhibitor hydroquinone, and 500 g of solvent isophorone were stirred, deoxygenated with nitrogen for 30 minutes, heated to 135°C, and subjected to ring-opening reaction for 7 hours. After cooling, a slightly yellow liquid was obtained, which was the target product, a divinyl-containing phosphoric acid functional monomer.

[0075] Example 1

[0076] This embodiment provides a method for preparing an aqueous negative electrode emulsion for a lithium battery, comprising the following steps:

[0077] S1: According to the weight percentage, add 0.5 parts of anionic emulsifier sodium lauryl sulfate and 1 part of nonionic emulsifier fatty alcohol polyoxyethylene ether into an emulsifier kettle, dissolve in 40 parts of deionized water, add 20 parts of styrene, 60 parts of oil-soluble acrylic ester monomer butyl acrylate, 5 parts of water-soluble monomer acrylic acid, and 5 parts of cross-linking monomer acrylamide after dissolution, stir at 500 rpm for 1 hour to obtain a pre-emulsion; take 100 parts for standby use;

[0078] S2: 5% of the weight of the pre-emulsion was added to the reaction kettle, and 0.1 parts by weight of initiator ammonium persulfate was added thereto, and stirred for 30 minutes to obtain a first reaction solution;

[0079] S3: raising the temperature of the first reaction liquid to 82° C. and starting constant temperature stirring to carry out polymerization reaction. After the reaction time is 1 hour, a second reaction liquid is obtained;

[0080] S4: continuously drip the remaining pre-emulsion and 0.3 parts by weight of initiator ammonium persulfate into the second reaction liquid, add 10 parts of divinyl-containing phosphoric acid functional monomer when the weight of the pre-emulsion is 20%, stir at 500 rpm for 10 minutes, and continue to drip the remaining pre-emulsion and the remaining initiator ammonium persulfate; after the addition, raise the temperature to 84°C, keep warm for 2 hours, add 2 parts of neutralizing agent sodium hydroxide, adjust the pH value to 6-8, pass cooling water to cool down to the polymerization kettle temperature of 40°C, filter through a 300-mesh filter to obtain a lithium battery aqueous negative electrode emulsion.

[0081] Example 2

[0082] This embodiment provides a method for preparing an aqueous negative electrode emulsion for a lithium battery, comprising the following steps:

[0083] S1: According to the weight ratio, add 1 part of anionic emulsifier sodium dodecylbenzene sulfonate and 0.5 parts of nonionic emulsifier Tween 80 in an emulsifying kettle, dissolve in 40 parts of deionized water, add 35 parts of styrene, 50 parts of oil-soluble acrylic ester monomer isooctyl acrylate, 7 parts of water-soluble monomer hydroxyethyl acrylate, and 3 parts of cross-linking monomer acryloyl morpholine after dissolution, stir at 500 rpm for 1 hour to obtain a pre-emulsion; take 100 parts for standby use;

[0084] S2: 6% of the weight of the pre-emulsion was added to the reaction kettle, and 0.05 parts by weight of initiator ammonium persulfate was added thereto, and stirred for 30 minutes to obtain a first reaction solution;

[0085] S3: raising the temperature of the first reaction liquid to 82° C. and starting constant temperature stirring to carry out polymerization reaction. After the reaction time is 1 hour, a second reaction liquid is obtained;

[0086] S4: continuously drip the remaining pre-emulsion and 0.15 parts by weight of initiator ammonium persulfate into the second reaction liquid, add 5 parts of divinyl-containing phosphoric acid functional monomer when the weight of the pre-emulsion is 20%, stir at 500 rpm for 10 minutes, and continue to drip the remaining pre-emulsion and the remaining initiator ammonium persulfate; after the addition, raise the temperature to 84°C, keep warm for 2 hours, add 3 parts of neutralizing agent sodium hydroxide, adjust the pH value to 6-8, pass cooling water to cool down to the polymerization kettle temperature of 40°C, filter through a 300-mesh filter to obtain a lithium battery aqueous negative electrode emulsion.

[0087] Example 3

[0088] This embodiment provides a method for preparing an aqueous negative electrode emulsion for a lithium battery, comprising the following steps:

[0089] S1: According to the weight ratio, 2 parts of anionic emulsifier sodium dodecyl diphenyl ether disulfonate and 0.2 parts of nonionic emulsifier fatty alcohol polyoxyethylene ether are added to an emulsifying kettle, and dissolved in 40 parts of deionized water. After dissolution, 50 parts of styrene, 30 parts of oil-soluble acrylic ester monomer butyl methacrylate, 10 parts of water-soluble monomer methacrylic acid, and 2 parts of cross-linking monomer hydroxyethyl acrylamide are added, and stirred at 500 rpm for 1 hour to obtain a pre-emulsion; 100 parts are taken for standby use;

[0090] S2: 10% of the weight of the pre-emulsion was added to a reaction kettle, and 0.075 parts by weight of initiator ammonium persulfate was added thereto, and stirred for 30 minutes to obtain a first reaction solution;

[0091] S3: raising the temperature of the first reaction liquid to 82° C. and starting constant temperature stirring to carry out polymerization reaction. After the reaction time is 1 hour, a second reaction liquid is obtained;

[0092] S4: continuously drip the remaining pre-emulsion and 0.225 parts by weight of initiator ammonium persulfate into the second reaction liquid, add 8 parts of divinyl-containing phosphoric acid functional monomer when the weight of the pre-emulsion is 20%, stir at 500 rpm for 10 minutes, and continue to drip the remaining pre-emulsion and the remaining initiator ammonium persulfate; after the addition, raise the temperature to 84°C, keep warm for 2 hours, add 4 parts of neutralizing agent sodium hydroxide, adjust the pH value to 6-8, pass cooling water to cool down to the polymerization kettle temperature of 40°C, filter through a 300-mesh filter to obtain a lithium battery aqueous negative electrode emulsion.

[0093] Comparative Example 1

[0094] The styrene acrylic emulsion in this comparative example adopts styrene acrylic emulsion LB300 produced by Japan Zeon Co., Ltd.

[0095] Comparative Example 2

[0096] The styrene acrylic emulsion in this comparative example adopts styrene acrylic emulsion 401 from Shenzhen Yanyi New Materials Co., Ltd.

[0097] Comparative Example 3

[0098] This comparative example provides a method for preparing an aqueous negative electrode emulsion for a lithium battery, comprising the following steps:

[0099] S1: According to the weight percentage, add 0.5 parts of anionic emulsifier sodium lauryl sulfate and 1 part of nonionic emulsifier fatty alcohol polyoxyethylene ether into an emulsifier kettle, dissolve in 40 parts of deionized water, add 20 parts of styrene, 60 parts of oil-soluble acrylic ester monomer butyl acrylate, 5 parts of water-soluble monomer acrylic acid, and 5 parts of cross-linking monomer acrylamide after dissolution, stir at 500 rpm for 1 hour to obtain a pre-emulsion; take 100 parts for standby use;

[0100] S2: 5% of the weight of the pre-emulsion was added to the reaction kettle, and 0.1 parts by weight of initiator ammonium persulfate was added thereto, and stirred for 30 minutes to obtain a first reaction solution;

[0101] S3: raising the temperature of the first reaction liquid to 82° C. and starting constant temperature stirring to carry out polymerization reaction. After the reaction time is 1 hour, a second reaction liquid is obtained;

[0102] S4: continuously drop the remaining pre-emulsion and 0.3 parts by weight of initiator ammonium persulfate into the second reaction liquid; after the addition, raise the temperature to 84°C, keep warm for 2 hours, add 2 parts of neutralizing agent sodium hydroxide, adjust the pH value to 6-8, pass cooling water to cool down the polymerization kettle temperature to 40°C, and filter through a 300-mesh filter to obtain a lithium battery aqueous negative electrode emulsion.

[0103] Comparative Example 4

[0104] This comparative example provides a method for preparing an aqueous negative electrode emulsion for a lithium battery, comprising the following steps:

[0105] S1: According to the weight percentage, add 0.5 parts of anionic emulsifier sodium lauryl sulfate and 1 part of nonionic emulsifier fatty alcohol polyoxyethylene ether into an emulsifier kettle, dissolve in 40 parts of deionized water, add 20 parts of styrene, 60 parts of oil-soluble acrylic ester monomer butyl acrylate, 5 parts of water-soluble monomer acrylic acid, 5 parts of cross-linking monomer acrylamide, 10 parts of divinyl-containing phosphoric acid functional monomer after dissolution, stir at 500 rpm for 1 hour to obtain a pre-emulsion; take 100 parts for standby use;

[0106] S2: 5% of the weight of the pre-emulsion was added to the reaction kettle, and 0.1 parts by weight of initiator ammonium persulfate was added thereto, and stirred for 30 minutes to obtain a first reaction solution;

[0107] S3: raising the temperature of the first reaction liquid to 82° C. and starting constant temperature stirring to carry out polymerization reaction. After the reaction time is 1 hour, a second reaction liquid is obtained;

[0108] S4: continuously drop the remaining pre-emulsion and 0.3 parts by weight of initiator ammonium persulfate into the second reaction liquid; after the addition, raise the temperature to 84°C, keep warm for 2 hours, add 2 parts of neutralizing agent sodium hydroxide, adjust the pH value to 6-8, pass cooling water to cool down the polymerization kettle temperature to 40°C, and filter through a 300-mesh filter to obtain a lithium battery aqueous negative electrode emulsion.

[0109] Comparative Example 5

[0110] This comparative example provides a method for preparing an aqueous negative electrode emulsion for a lithium battery, comprising the following steps:

[0111] S1: According to the weight percentage, add 0.5 parts of anionic emulsifier sodium lauryl sulfate and 1 part of nonionic emulsifier fatty alcohol polyoxyethylene ether into an emulsifier kettle, dissolve in 40 parts of deionized water, add 20 parts of styrene, 60 parts of oil-soluble acrylic ester monomer butyl acrylate, 5 parts of water-soluble monomer acrylic acid, and 5 parts of cross-linking monomer acrylamide after dissolution, stir at 500 rpm for 1 hour to obtain a pre-emulsion; take 100 parts for standby use;

[0112] S2: 5% of the weight of the pre-emulsion was added to the reaction kettle, and 0.1 parts by weight of initiator ammonium persulfate was added thereto, and stirred for 30 minutes to obtain a first reaction solution;

[0113] S3: raising the temperature of the first reaction liquid to 82° C. and starting constant temperature stirring to carry out polymerization reaction. After the reaction time is 1 hour, a second reaction liquid is obtained;

[0114] S4: continuously drip the remaining pre-emulsion and 0.3 parts by weight of initiator ammonium persulfate into the second reaction liquid, add 10 parts of divinylbenzene (DVB) when the weight of the pre-emulsion is 20%, stir at 500 rpm for 10 minutes, and continue to drip the remaining pre-emulsion and the remaining initiator ammonium persulfate; after the addition, raise the temperature to 84°C, keep warm for 2 hours, add 2 parts of neutralizing agent sodium hydroxide, adjust the pH value to 6-8, pass cooling water to cool down to the polymerization kettle temperature of 40°C, filter through a 300-mesh filter to obtain a lithium battery aqueous negative electrode emulsion.

[0115] The aqueous negative electrode emulsions of lithium batteries prepared in the above-mentioned embodiments and comparative examples were used as binders to prepare negative electrode plates and soft-pack batteries. The specific design information of the batteries is as follows in Table 1:

[0116] ,

[0117] The performance of the prepared pole piece and lithium-ion battery was tested, and the test method was as follows:

[0118] Pole piece peeling force: The pole piece is cut into 50mm*20mm, and the high-speed tensile machine is used at a speed of 50mm / min to measure the 180° peeling test.

[0119] DCR reduction percentage: 25℃, 50% SOC-5C discharge for 30s, DCR value (in milliohms), relative DCR reduction percentage of LB300.

[0120] Full charge rebound rate: Fully charge the battery at 25℃ 1C, disassemble the battery, and measure the thickness of the negative electrode with a micrometer.

[0121] Rebound rate % = (pole piece thickness - initial pole piece thickness) / (initial pole piece thickness - foil thickness).

[0122] High temperature cycle: The thermostat was adjusted to 55°C, the battery was placed in the thermostat for 4 hours, then charged at 1C and discharged at 1C for high temperature cycle, and the battery capacity retention rate was collected after 800 cycles.

[0123] The test results are shown in Table 2:

[0124] .

[0125] It can be seen from the data in Table 1 above that the aqueous negative electrode emulsions for lithium batteries provided by the embodiments of the present invention have a high electrode peeling force when used in lithium-ion batteries, can inhibit the rebound of graphite when fully charged, and have excellent high-temperature cycle performance.

[0126] The difference between Comparative Example 3 and Example 1 is that the homemade divinyl-containing phosphate functional monomer is not added during the preparation process. Due to the lack of phosphate functional groups and the decrease in cross-linking density, the prepared lithium battery aqueous negative electrode emulsion has lower negative electrode peeling force than the lithium battery aqueous negative electrode emulsion provided in Example 1, a larger full-charge rebound, and a poor battery high-temperature cycle capacity retention rate.

[0127] The difference between Comparative Example 4 and Example 1 is that during the preparation process, the homemade divinyl-containing phosphate functional monomer is directly added to the pre-emulsion. Because the phosphate functional group is encapsulated inside the latex particles, the prepared lithium battery aqueous negative electrode emulsion has a lower negative electrode stripping force than the lithium battery aqueous negative electrode emulsion provided in Example 1, the DCR decreases insignificantly, and the high temperature cycle retention rate is poor.

[0128] The difference between Comparative Example 5 and Example 1 is that divinylbenzene is used to replace the divinyl-containing phosphate functional monomer during the preparation process. Due to the lack of phosphate groups and the short divinylbenzene chain segments, the synthesized emulsion is hard and brittle, resulting in a more significant decrease in the negative electrode stripping force of the prepared lithium battery aqueous negative electrode emulsion than the lithium battery aqueous negative electrode emulsion provided in Example 1, and a poor high-temperature cycle retention rate.

[0129] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A lithium battery aqueous negative electrode emulsion, characterized in that: According to parts by weight, it includes the following components: Pre-emulsion 100 parts; 5-10 parts of a divinyl-containing phosphoric acid functional monomer; 2-4 parts of neutralizer; Initiator 0.2-0.4 parts; Water 60 parts; The divinyl-containing phosphoric acid functional monomer is prepared according to the following method: Pentaerythritol phosphate, glycidyl methacrylate, a polymerization inhibitor, and a solvent are mixed, deoxygenated, and then heated to 130-140° C. for a ring-opening reaction to obtain the divinyl-containing phosphoric acid functional monomer; The aqueous negative electrode emulsion for lithium batteries is prepared according to the following method: S1: Dissolve anionic emulsifier and nonionic emulsifier in water according to the formula, add styrene, oil-soluble acrylic ester monomer, water-soluble monomer and cross-linking monomer, stir to obtain a pre-emulsion; S2: according to the formula, water and part of the pre-emulsion are mixed, and part of the initiator is added and stirred to obtain a first reaction liquid; S3: raising the temperature of the first reaction liquid to 82-84° C., stirring at a constant temperature to carry out polymerization reaction, to obtain a second reaction liquid; S4: adding the remaining pre-emulsion, the remaining initiator and the divinyl-containing phosphate functional monomer to the second reaction liquid for reaction. After the reaction is completed, cooling to 50° C., adding a neutralizer, adjusting the pH to 6-8, stirring, and then lowering the temperature to 40-45° C., filtering, and obtaining a lithium battery aqueous negative electrode emulsion.

2. The aqueous negative electrode emulsion for lithium batteries according to claim 1, characterized in that: The pre-emulsion comprises the following components in parts by weight: Styrene 20-50 parts; 30-60 parts of oil-soluble acrylic monomer; 5-10 parts of water-soluble monomer; 2-5 parts of cross-linking monomer; Anionic emulsifier 0.5-2 parts; Nonionic emulsifier 0.2-1 part; 40 parts water.

3. The aqueous negative electrode emulsion for lithium batteries according to claim 1, characterized in that: The molar ratio of the pentaerythritol phosphate to the glycidyl methacrylate is 1:

2.

4. The aqueous negative electrode emulsion for lithium batteries according to claim 2, characterized in that: The oil-soluble acrylic acid ester monomer is selected from at least one of butyl acrylate, isooctyl acrylate, butyl methacrylate, methyl methacrylate, isobornyl methacrylate and octadecyl acrylate.

5. The aqueous negative electrode emulsion for lithium batteries according to claim 2, characterized in that: The water-soluble monomer is selected from at least one of acrylic acid, methacrylic acid, itaconic acid, hydroxyethyl acrylate and hydroxyethyl methacrylate.

6. The aqueous negative electrode emulsion for lithium batteries according to claim 2, characterized in that: The cross-linking monomer is selected from at least one of acrylamide, acryloylmorpholine, hydroxyethyl acrylamide, diacetone acrylamide and silicone monomer.

7. The aqueous negative electrode emulsion for lithium batteries according to claim 2, characterized in that: The anionic emulsifier is at least one selected from sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium dodecyl diphenyl ether disulfonate, and sodium dioctyl sulfonated succinate.

8. The aqueous negative electrode emulsion for lithium batteries according to claim 2, characterized in that: The nonionic emulsifier is selected from at least one of fatty alcohol polyoxyethylene ether, Tween 80, and alkyl alcohol polyether.