Composite aqueous binder and application thereof in lithium secondary battery
By using composite water-based binders in the positive electrode of lithium-ion battery, combined with the synergistic effect of low molecular weight and high molecular weight materials, the shortcomings of existing lithium-ion battery positive electrode water-based binders in terms of first-effect and high-temperature cycle stability are solved, and higher electrochemical performance and environmental friendliness are achieved.
Patent Information
- Application Number
- CN202311692490.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-11
- Publication Date
- 2025-06-13
AI Technical Summary
The water-based binders of the positive electrode of the existing lithium-ion battery are poor in terms of first-effect and high-temperature cycle stability, and commonly used binders such as PVDF require the use of toxic N-methylpyrrolidone as a dispersant, which affects environmental friendliness and costs.
A composite water-based adhesive is used, which consists of a low molecular weight polymer such as sodium alginate with a molecular weight less than 10,000 and a high molecular weight material such as gelatin with a molecular weight between 100,000 and 500,000. By adjusting the ratio and molecular weight of component A and component B, synergistic effects are achieved, and adhesion and solid content are improved.
The first effect and high-temperature cycle stability of the lithium-ion battery positive electrode are significantly improved, and the difficulty of drying of the water-based slurry is reduced. Moreover, since all water-soluble materials are used, the use of toxic solvents is avoided, and environmental friendliness is improved.
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Figure CN120137557A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of new energy, and particularly relates to an electrode binder for lithium secondary batteries. Technical Background
[0002] With the continuous development of lithium-ion batteries, the research on various fields of lithium-ion batteries has become more and more in-depth. The binder is an indispensable component in lithium-ion batteries. Its function is to firmly bond the positive and negative electrode materials to the metal current collector, enhance the contact between the active material and the conductive agent and between the active material and the current collector, and at the same time stabilize the structure of the electrode sheet, constituting the positive and negative electrode sheets of the battery. The dosage of the binder is generally 2%-5% of the active material. Although the dosage is small, it often has an unignorable impact on the performance of the active material and thus on the performance of the entire battery.
[0003] Currently, aqueous binders are mainly developed for graphite and silicon-carbon anodes, and the development of aqueous binders for corresponding cathode materials has stagnated. As an important component of lithium-ion batteries, the currently commonly used binder for cathode materials is still PVDF. However, it has a high swelling rate in the electrolyte, poor mechanical properties and adhesion, which is not conducive to the long-term use of the battery. Moreover, it needs to use toxic N-methylpyrrolidone (NMP) as a dispersant, which is not environmentally friendly and has a high cost.
[0004] Currently, the aqueous binders used for lithium-ion battery cathodes mainly include polyacrylonitrile, polyacrylic acid, polyacrylate, sodium alginate, etc. However, when these polymers are used as lithium-ion battery binders, relatively high molecular weights are usually used. However, relatively high molecular weights also bring corresponding problems. When these polymers are used as binders, their binding principle is different from that of PVDF which relies on weak van der Waals forces. Usually, these polymers will have a bonding effect with the abundant functional groups on the surface of electrode particles, such as hydrogen bonds or ester bonds. Therefore, at the same solid content, the viscosity of the slurry prepared with these polymers is much higher than that of the slurry prepared with PVDF + N-methylpyrrolidone. Usually, water addition is used to adjust it, which will result in a low solid content of the slurry prepared with the aqueous binder, being not conducive to subsequent drying. In addition, the initial efficiency and high-temperature cycle stability of the prepared electrode sheets such as cathodes are not ideal. Therefore, there is an urgent need to provide an aqueous binder that can improve the cycle stability of lithium-ion batteries. Summary of the Invention
[0005] Aiming at the disadvantages that the initial efficiency and high-temperature cycle stability of the electrode sheets obtained by the current aqueous binders are not ideal, the first object of the present invention is to provide a brand-new composite aqueous binder, aiming to improve the electrochemical performance of the prepared electrodes, especially the initial efficiency and high-temperature cycle stability.
[0006] The second object of the present invention is to provide the application of the composite aqueous binder in the preparation of lithium secondary batteries and their positive electrodes.
[0007] A composite aqueous binder, comprising component A and component B with a weight ratio of 70-95:30-5;
[0008] Wherein, component A is at least one of sodium alginate, polymethyl methacrylate, sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, and polyvinylpyrrolidone with a molecular weight less than 10,000;
[0009] The said component B is at least one of gelatin, sodium carboxymethyl cellulose, guar gum, polyacrylic acid, styrene-butadiene rubber, hydroxyethyl cellulose, and starch with a molecular weight in the range of 100,000-5,000,000.
[0010] The present invention innovatively combines the said components and components A and B with molecular weights, and further cooperates with the combined control of the ratio of the two, so that synergism can be unexpectedly achieved, and the initial efficiency and high-temperature cycle stability of the composite aqueous binder added can be significantly improved.
[0011] In the present invention, in the said component A and component B, the said molecular weight index is the molecular weight.
[0012] In the present invention, the combined control of the components, molecular weights, and component ratios of component A and component B is the key to synergistically improving the initial efficiency and high-temperature performance of their composite positive electrode. The research also found that further optimizing the control of the types, molecular weights, and ratios of component A and component B can further improve the synergistic effect, which helps to further improve the initial efficiency and high-temperature stability of the prepared electrode.
[0013] Preferably, the molecular weight of component A is 2,000-8,000, preferably 2,500-5,500; more preferably 3,000-5,000;
[0014] Preferably, component A is at least one of polymethyl methacrylate, sodium carboxymethyl cellulose, polyacrylic acid, and polyvinyl alcohol.
[0015] Preferably, the molecular weight of component B is 100,000-550,000, and more preferably 150,000-450,000.
[0016] Preferably, component B is at least one of sodium carboxymethyl cellulose, guar gum, polyacrylic acid, and hydroxyethyl cellulose.
[0017] Preferably, the weight ratio of component A to component B is: 90-75:10-25;
[0018] Preferably, there is no chemical crosslinking between component A and component B.
[0019] In the present invention, the composite aqueous binder can be obtained by mixing based on a known mixing process.
[0020] The present invention also provides an application of the composite aqueous binder, using it as a binder for preparing an electrode;
[0021] Preferably, the electrode is an electrode of a lithium secondary battery, preferably a positive electrode;
[0022] Preferably, the composite aqueous binder, the positive electrode active material, and the conductive agent are compounded and slurried to form a positive electrode slurry, and then coated on a positive electrode current collector and dried to obtain;
[0023] Preferably, the drying method is negative pressure drying;
[0024] Preferably, the temperature in the drying stage is below 80 °C. For example, the drying temperature is 60 - 80 °C, and the drying time can be more than 5 h, and further can be 8 - 12 hours.
[0025] The present invention also provides a positive electrode of a lithium secondary battery, including a positive electrode current collector and a positive electrode material compounded on its surface. The positive electrode material includes a positive electrode active material, a conductive agent, and a binder. Among them, the binder contains the composite aqueous binder of the present invention.
[0026] In the present invention, in the binder, the content of the composite aqueous binder is above 10 wt.%, preferably above 50 wt.%, further preferably above 90 wt.%; more preferably, it is the composite aqueous binder;
[0027] In the present invention, the positive electrode active material can be a positive electrode active material well-known in the industry. For example, its expression can be LiXO 2 , LiYnO 4 , LiZPO 4 or at least one of them;
[0028] Preferably, X is at least one of Ni, Mn, and Co; Y is at least one of Ni and Mn, n is 1 or 2; Z is at least one of Fe and Mn;
[0029] In the present invention, the positive electrode active material includes but is not limited to lithium iron phosphate (LiFePO 4 ), lithium manganese iron phosphate (LiMn x Fe 1-x O 4 ), lithium manganate (LiMn 2 O 4 ), lithium nickel manganate (LiNi xMn 2-x O 4 ) one or more of nickel-cobalt-manganese ternary (LiNi x Co y Mn 1-x-y O 2 ) and lithium cobaltate;
[0030] In the present invention, the conductive agent can be a carbon material with conductivity known in the industry, such as one or more of acetylene black, conductive carbon black, carbon nanotubes and graphene.
[0031] In the present invention, in the positive electrode material, the mass ratio of the positive electrode active material, the conductive agent, and the composite aqueous binder is (60-90):(5-20):(5-20), and further can be (75-85):(5-15):(5-15).
[0032] The present invention also provides a lithium secondary battery, including an electric core and an electrolyte for soaking the electric core. The electric core includes a positive electrode, a separator and a negative electrode which are sequentially compounded. It is characterized in that the positive electrode is the positive electrode containing the composite aqueous binder in the present invention.
[0033] Beneficial effects:
[0034] 1. The present invention provides a brand-new composite aqueous binder, which innovatively realizes synergy by the combination of component A and component B with the said molecular weight, and further cooperates with the combined control of the ratio of the two. In this way, it can unexpectedly improve the adhesiveness of the binder, improve the solid content in the aqueous slurry, reduce the drying difficulty of the aqueous slurry. In addition, it can also significantly improve the initial efficiency and high-temperature cycle stability of the prepared electrode, such as the positive electrode.
[0035] 2. The materials adopted in the present invention are all water-soluble materials, and N-methylpyrrolidone does not need to be used, which is environmentally friendly. Description of the drawings
[0036] Figure 1 It is the microscopic morphology diagram (SEM) of Comparative Example 1;
[0037] Figure 2 It is the microscopic morphology diagram (SEM) of Comparative Example 2;
[0038] Figure 3 It is the cycle diagram of Example 1, Example 2, Example 3, Comparative Example 3, Comparative Example 4 and Comparative Example 5 at 60 °C;
[0039] Figure 4 It is the cycle diagram of Example 4 and Comparative Example 6 at 60 °C. Specific embodiments
[0040] Example 1
[0041] Step (1): Preparation of aqueous binder
[0042] Take component A (polyvinyl alcohol with a molecular weight of 5000) and dissolve it in water, then add component B (hydroxyethyl cellulose with a molecular weight of 150000). The weight ratio of component A to component B is 80:20. After stirring evenly, an aqueous binder is obtained, and the total mass concentration of component A and component B is 10%.
[0043] Step (2): Preparation of the positive electrode
[0044] Prepare a slurry with lithium manganate (LiMn 2 O 4 ): conductive additive (conductive carbon black): the binder in step 1 (calculated by the weight of the solute therein, that is, the total amount of component A and component B) = 80:10:10. Then coat it on the Al foil and dry it at 75 - 80 °C for 8 h to obtain the electrode sheet prepared in Example 1.
[0045] Step (3): Battery assembly and testing
[0046] After drying the positive electrode sheet in step (2), cut it into circular pieces with a diameter of 12 mm for standby. Battery assembly is carried out in a super purification glove box, and a button-type half-cell is assembled in the order of the positive electrode shell, positive electrode circular piece, electrolyte, separator, electrolyte, lithium metal circular piece, nickel foam mesh and negative electrode shell. After assembly, let it stand for 4 - 6 h, take the battery to a blue battery system at 60 °C for electrochemical cycling testing. After activating for 3 cycles at 0.1C, 0.2C and 0.5C, perform high-temperature cycling testing at a current density of 1C. There are no special requirements for the electrolyte used, and it is a common ester-based electrolyte in the industry with good lithium-ion transmission ability {in this case, the electrolyte is 1M LiPF 6 + ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 1:1:1, volume ratio, and add 3 wt% of fluoroethylene carbonate (FEC) by total mass}.
[0047] Its cycling performance at high temperature (60 °C) is as Figure 3 shown. The capacity retention rate reaches 96.51% at a current density of 1C for 150 cycles. Its initial efficiency is 95.28%.
[0048] Example 2
[0049] Compared with Example 1, the difference is only that component A is polyacrylic acid with a molecular weight of 3000, component B is hydroxyethyl cellulose with a molecular weight of 150000, and the ratio of component A to component B is 80:20; other operations and tests such as the total amount of component A and component B are the same as those in Example 1.
[0050] Its cycling performance at high temperature (60 °C) is as follows Figure 3 shown. The capacity retention rate reaches 97.17% at a current density of 1C for 150 cycles. Its initial efficiency is 95.36%.
[0051] Example 3
[0052] Compared with Example 1, the only difference is that Component A is polyacrylic acid with a molecular weight of 3000, Component B is sodium carboxymethyl cellulose with a molecular weight of 400000, and the ratio of Component A to Component B is 80:20; other operations and tests such as the total amount of Component A and Component B are the same as in Example 1.
[0053] Its cycling performance at high temperature (60 °C) is as follows Figure 3 shown. The capacity retention rate reaches 96.26% at a current density of 1C for 150 cycles. Its initial efficiency is 96.75%.
[0054] Example 4
[0055] Compared with Example 1, the only difference is that the active material in Step 2 is replaced with lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O 4 ), and other operations and parameters are the same as in Example 1.
[0056] Its cycling performance at high temperature (60 °C) is as follows Figure 4 shown. The capacity retention rate reaches 96.46% at a current density of 1C for 80 cycles.
[0057] Example 5
[0058] Compared with Example 1, the only difference is that the molecular weight and type of Component A are changed. The experimental groups are as follows:
[0059] A: Component A is polymethyl methacrylate with a molecular weight of 3000
[0060] B: Component A is polyvinylpyrrolidone with a molecular weight of 3000
[0061] C: Component A is sodium carboxymethyl cellulose with a molecular weight of 5000
[0062] Tested in the manner of Example 1, the results are shown in Table 1. After changing the type and molecular weight of Component A, its capacity retention rate can also reach a relatively high level, higher than that of the currently common polyvinylidene fluoride binder.
[0063] Example 6
[0064] Compared with Example 1, the only difference is that the molecular weight and type of Component B are changed. The experimental groups are as follows:
[0065] A: Component B is polyacrylic acid with a molecular weight of 450,000;
[0066] B: Component B is starch with a molecular weight of 300,000;
[0067] C: Component B is guar gum with a molecular weight of 350,000;
[0068] The test was carried out in the same manner as in Example 1, and the results are shown in Table 1. After changing the type and molecular weight of Component B, its capacity retention rate can also reach a relatively high level, higher than that of the currently common polyvinylidene fluoride binder.
[0069] Example 7
[0070] Compared with Example 1, the difference is only that, with the total amount of Component A and Component B remaining unchanged, the ratio of Component A to Component B is changed, and the experimental groups are as follows:
[0071] A: The ratio of Component A to Component B is 90:10;
[0072] B: The ratio of Component A to Component B is 75:25;
[0073] The test was carried out in the same manner as in Example 1, and the results are shown in Table 1. By only changing the ratio of Component A to Component B, its capacity retention rate can also reach a relatively high level.
[0074] Example 8
[0075] Compared with Example 1, the difference is only that in step (2), the weight ratio of lithium manganate (LiMn 2 O 4 ) : conductive additive (conductive carbon black) : binder in step 1 (calculated by the weight of the solute therein, that is, the total amount of Component A and Component B therein) is 80:5:15.
[0076] The test was carried out according to the method of Example 1, and the results are as follows: The cycling performance at high temperature (60 °C) is shown in Table 1, and the capacity retention rate at a current density of 1C for 150 cycles reached 92.29%. Its initial efficiency is 94.52%.
[0077] Example 9
[0078] Compared with Example 1, the difference is only that in step (2), the weight ratio of lithium manganate (LiMn 2 O 4 ) : conductive additive (conductive carbon black) : binder in step 1 (calculated by the weight of the solute therein, that is, the total amount of Component A and Component B therein) is 80:15:5.
[0079] The test was carried out according to the method of Example 1. The results were as follows: The cycling performance at high temperature (60 °C) is shown in Table 1. The capacity retention rate reached 92.25% at a 1C current density after 150 cycles. Its initial efficiency was 94.78%.
[0080] Comparative Example 1
[0081] Compared with Example 1, the difference is only that in the aqueous binder, component A is missing, and the missing weight is supplemented by an equal weight of component B therein. Other operations and parameters are the same as those in Example 1.
[0082] Figure 1 The SEM image of the electrode sheet prepared in Comparative Example 1 shows that although the conductive additive uniformly coats the surface of the positive electrode particles, the contact between the positive electrode particles is not tight, which affects the electrochemical performance.
[0083] The test was carried out in the same manner as in Example 1. The results are shown in Table 1. Its retention rate is lower than that of Example 1.
[0084] Comparative Example 2
[0085] Compared with Example 1, the difference is only that in the aqueous binder, component B is missing, and the missing weight is supplemented by an equal weight of component A therein. Other operations and parameters are the same as those in Example 1.
[0086] Figure 2 The SEM image of the electrode sheet prepared in Comparative Example 2 shows that the conductive additive cannot uniformly coat the surface of the positive electrode particles, and obvious agglomeration will occur, which affects the electrochemical performance.
[0087] The test was carried out in the same manner as in Example 1. The results are shown in Table 1. Its retention rate is lower than that of Example 1.
[0088] Comparative Example 3
[0089] Compared with Example 1, the difference is only that component A is polyvinyl alcohol with a molecular weight of 100,000, and other operations and parameters are the same as those in Example 1
[0090] The test was carried out in the same manner as in Example 1. The results are as Figure 3 shown. The capacity retention rate reached 81.87% at a 1C current density after 150 cycles, and a large decrease occurred around 100 cycles.
[0091] Comparative Example 4
[0092] Compared with Example 1, the difference is only that component B is hydroxyethyl cellulose with a molecular weight of 10,000, and other operations and parameters are the same as those in Example 1
[0093] The test was carried out in the same manner as in Example 1. The results are as Figure 3As shown, the capacity retention rate reached 84.29% at a 1C current density for 150 cycles, and there was a significant decline around 100 cycles.
[0094] Comparative Example 5
[0095] Compared with Example 1, the only difference is that the most commonly used polyvinylidene fluoride is used as the binder, and N-methylpyrrolidone is used as the solvent, and other operations and parameters are the same as those in Example 1.
[0096] There are no special requirements for the molecular weight of the polyvinylidene fluoride and N-methylpyrrolidone.
[0097] Its cycling performance at high temperature (60 °C) is as Figure 3 shown. The capacity retention rate reached 86.91% at a 1C current density for 150 cycles. Its initial efficiency was 93.25%.
[0098] Comparative Example 6
[0099] Compared with Comparative Example 5, the only difference is that the cathode material used is lithium nickel manganate (LiNi 0.5 Mn 1.5 O 4 ), and other operations and parameters are the same as those in Comparative Example 5;
[0100] Its cycling performance at high temperature (60 °C) is as Figure 4 shown. It experienced a significant capacity decay at the beginning of the high-temperature cycle.
[0101] Table 1 shows the specific cycling data of Example 5, Example 6, Example 7, Example 8, Example 9 and Comparative Example 1, Comparative Example 2 at a high temperature of 60 °C.
[0102] Table 1 Cycling performance data of specific cases
[0103]
[0104]
[0105] It can be seen from Table 1 that by using the composite aqueous binder described in the present invention, under a variety of different binder combinations, it is unexpectedly possible to achieve synergy and obtain better high-temperature cycling stability.
Claims
1. A composite aqueous binder, characterized in that, it comprises component A and component B with a weight ratio of 70 - 95:30 - 5; wherein, component A is at least one of sodium alginate, polymethyl methacrylate, sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, and polyvinylpyrrolidone with a molecular weight less than 10,000; the said component B is at least one of gelatin, sodium carboxymethyl cellulose, guar gum, polyacrylic acid, styrene - butadiene rubber, hydroxyethyl cellulose, and starch with a molecular weight in the range of 100,000 - 5,000,000.
2. The composite aqueous binder according to claim 1, characterized in that, in the said component A and component B, the said molecular weight is the number - average molecular weight.
3. The composite aqueous binder according to claim 1 or 2, characterized in that, the molecular weight of the said component A is 2,000 - 8,000, preferably 2,500 - 5,500; preferably, the said component A is at least one of polymethyl methacrylate, sodium carboxymethyl cellulose, polyacrylic acid, and polyvinyl alcohol.
4. The composite aqueous binder according to claim 3, characterized in that, the molecular weight of the said component B is 100,000 - 550,000; preferably, the said component B is at least one of sodium carboxymethyl cellulose, guar gum, polyacrylic acid, and hydroxyethyl cellulose.
5. The composite aqueous binder according to claim 4, characterized in that, the weight ratio of component A and component B is: 90 - 75:10 - 25; preferably, there is no chemical cross - linking between the said component A and component B.
6. An application of the composite aqueous binder according to any one of claims 1 - 5, characterized in that, using it as a binder for preparing an electrode; preferably, the said electrode is an electrode of a lithium secondary battery, preferably a positive electrode; preferably, forming a positive electrode paste by compounding and slurrying the said composite aqueous binder, a positive electrode active material, and a conductive agent, and then coating it on a positive electrode current collector and drying to obtain; preferably, the said drying method is negative - pressure drying; preferably, the temperature in the said drying stage is below 80 °C.
7. A positive electrode of a lithium secondary battery, comprising a positive electrode current collector and a positive electrode material composite on its surface, and the said positive electrode material comprises a positive electrode active material, a conductive agent, and a binder, characterized in that, the said binder contains the composite aqueous binder according to any one of claims 1 - 5.
8. The positive electrode of a lithium secondary battery according to claim 7, characterized in that, in the said binder, the content of the said composite aqueous binder is above 10 wt.%, preferably above 50 wt.%, further preferably above 90 wt.%; even more preferably, it is the said composite aqueous binder; Preferably, the expression of the positive electrode active material is LiXO 2 , LiYnO 4 , LiZPO 4 or at least one of them; preferably, the said X is at least one of Ni, Mn, and Co; the said Y is at least one of Ni and Mn, and the said n is 1 or 2; the said Z is at least one of Fe and Mn; preferably, the said positive electrode active material includes but is not limited to one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium nickel manganate, and lithium cobaltate. Preferably, the conductive agent is one or more of acetylene black, conductive carbon black, carbon nanotubes, and graphene.
9. The positive electrode of the lithium secondary battery according to claim 7 or 8, characterized in that in the positive electrode material, the mass ratio of the positive electrode active material, the conductive agent, and the composite aqueous binder is (60-90):(5-20):(5-20).
10. A lithium secondary battery, comprising an electric core and an electrolyte for soaking the electric core, and the electric core comprises a positive electrode, a separator, and a negative electrode which are sequentially laminated, characterized in that the positive electrode is the positive electrode according to any one of claims 7 to 9.