A positive electrode sheet, a method for manufacturing the same, and use thereof

Abstract

The application belongs to the technical field of batteries, and particularly relates to a positive pole piece, a preparation method and application thereof. The positive pole piece comprises a current collector, a first positive pole slurry coating and a second positive pole slurry coating which are sequentially coated on the current collector; the second positive pole slurry coating comprises the following raw materials: an oxide solid-state electrolyte, a polyphosphazene compound, a second binder and a second solvent. The positive pole piece has the beneficial effects that the positive pole piece can effectively prevent the diffusion of heat inside the battery, can avoid thermal runaway of the battery, and effectively improves the safety performance of the battery without affecting the performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a positive electrode sheet, its preparation method, and its application. Background Technology

[0002] In recent years, the industrialization of solid-state batteries has accelerated. Solid-state battery technology routes include semi-solid-state and all-solid-state. Semi-solid-state batteries are considered a transitional approach, while all-solid-state batteries need to address issues such as interface processing, material stability, and high cost. Solid-state batteries face difficulties in large-scale replacement of liquid batteries, especially given the low-cost advantage of lithium iron phosphate batteries. However, solid-state batteries offer advantages such as high energy density and good safety performance, and their applications mainly include electric vehicles, consumer electronics, aerospace, and medical devices.

[0003] Currently, the energy density of ternary liquid batteries is nearing its limit, and their safety is also a concern. Meanwhile, the energy density of semi-solid batteries has reached 360Wh / kg, and further breakthroughs are expected, with a high probability of exceeding the 500Wh / kg mark, providing longer driving ranges for electric vehicles and other applications. At the same time, by introducing a solid electrolyte layer, semi-solid batteries can reduce side reactions between electrode materials and electrolytes, thereby improving the battery's electrical and safety performance.

[0004] To improve the energy density of semi-solid-state batteries, existing technologies often employ methods such as using high-nickel materials, increasing battery voltage, increasing the coating density of positive and negative electrodes, increasing electrode compaction, and reducing electrolyte injection. However, these methods, on the one hand, reduce the battery's electrical performance, and on the other hand, increase safety risks. Batteries assembled with high-nickel materials, once experiencing abnormalities such as short circuits, overcharging, or over-discharging, will experience a rapid rise in temperature, leading to thermal runaway, fire, and explosion, causing safety accidents. Summary of the Invention

[0005] This application provides a positive electrode sheet, its preparation method, and its application, aiming to solve the problem that existing batteries experience a rapid rise in battery temperature, leading to battery fires and explosions when faced with abnormalities such as short circuits, overcharging, and over-discharging.

[0006] The first aspect of this application provides a positive electrode sheet comprising a current collector, a first positive electrode slurry coating and a second positive electrode slurry coating sequentially coated on the current collector;

[0007] The second positive electrode slurry coating comprises the following raw materials: oxide solid electrolyte, polyphosphazene compound, second binder and second solvent.

[0008] According to some embodiments of the positive electrode sheet described in this application, the second positive electrode slurry coating comprises the following raw materials in parts by weight: 85-95 parts of oxide solid electrolyte, 1.5-5 parts of polyphosphazene compound, and 3.5-10 parts of second binder.

[0009] According to some embodiments of the positive electrode sheet described in this application, the oxide solid electrolyte includes one or more of lithium titanium aluminum phosphate, lithium lanthanum titanium oxide, and lithium lanthanum zirconium oxide.

[0010] According to some embodiments of the positive electrode sheet described in this application, the chemical formula of the polyphosphazene compound is: -[-N=P(R1R2)-]- n ,

[0011] R1 includes pyrrolidone;

[0012] R2 is selected from compounds with the following structural formulas:

[0013] M is selected from alkyl, Li, Na or K;

[0014] 500≤n≤20000.

[0015] According to some embodiments of the positive electrode sheet described in this application, the second binder comprises polyvinylidene fluoride.

[0016] According to some embodiments of the positive electrode sheet described in this application, the second solvent includes N-methylpyrrolidone.

[0017] According to some embodiments of the positive electrode sheet described in this application, the chemical formula of the polyphosphazene compound is: -[-N=P(R1R2)-]- n ,

[0018] R1 is selected from compounds with the following structural formulas:

[0019]

[0020] The structure of R2 is shown in the following equation:

[0021] M is selected from CH3, C2H5, C3H7, and C4H9.

[0022] According to some embodiments of the positive electrode sheet described in this application, the particle size of the oxide solid electrolyte is 100-1000 nm.

[0023] According to some embodiments of the positive electrode sheet described in this application, the thickness of the second positive electrode slurry coating is 2-8 μm.

[0024] According to some embodiments of the positive electrode sheet described in this application, the current collector includes an aluminum foil current collector.

[0025] According to some embodiments of the positive electrode sheet described in this application, the first positive electrode slurry coating includes a positive electrode active material, a conductive agent, a first binder, and a first solvent;

[0026] According to some embodiments of the positive electrode sheet described in this application, the positive electrode active material includes lithium nickel cobalt manganese oxide.

[0027] According to some embodiments of the positive electrode sheet described in this application, the conductive agent includes conductive carbon black.

[0028] According to some embodiments of the positive electrode sheet described in this application, the first binder includes polyvinylidene fluoride.

[0029] According to some embodiments of the positive electrode sheet described in this application, the first solvent includes N-methylpyrrolidone.

[0030] A second aspect of this application provides a method for preparing the positive electrode sheet described in the first aspect of this application, comprising the following steps:

[0031] (1) The first positive electrode slurry is coated onto the current collector and dried to obtain the first positive electrode slurry coating;

[0032] (2) The second positive electrode slurry is coated on the surface of the first positive electrode slurry coating, dried, and rolled to obtain the positive electrode sheet.

[0033] The third aspect of this application provides the application of the positive electrode sheet described in the first aspect of this application or the positive electrode sheet obtained by the preparation method described in the second aspect of this application in a semi-solid-state battery.

[0034] The beneficial effects of this application include: the positive electrode sheet described in this application can effectively prevent heat dissipation inside the battery, avoid thermal runaway of the battery, and effectively improve the safety performance of the battery without affecting the battery performance. Detailed Implementation

[0035] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0036] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0037] This application provides a positive electrode sheet, including a current collector, a first positive electrode slurry coating and a second positive electrode slurry coating sequentially coated on the current collector;

[0038] The second positive electrode slurry coating comprises the following raw materials: oxide solid electrolyte, polyphosphazene compound, second binder and second solvent.

[0039] The positive electrode sheet described in this application further increases the electrode contact resistance by coating a layer containing polyphosphazene compound and solid electrolyte on the coated ternary positive electrode sheet, thereby reducing the risk of thermal runaway and improving the safety performance of the battery in the event of internal short circuit or other thermal abuse of the lithium-ion battery.

[0040] In some embodiments of this application, the second positive electrode slurry coating comprises the following raw materials in parts by weight: 85-95 parts of oxide solid electrolyte, 1.5-5 parts of polyphosphazene compound, and 3.5-10 parts of second binder.

[0041] In some embodiments of this application, the oxide solid electrolyte includes one or more of lithium titanium aluminum phosphate, lithium lanthanum titanium oxide, and lithium lanthanum zirconium oxide.

[0042] Oxide solid electrolytes possess high thermal stability and non-flammability, effectively addressing the safety issues of ternary lithium-ion batteries. Coating electrode surfaces with oxide solid electrolyte layers leverages their high thermal stability and ionic conductivity, effectively enhancing cell safety without compromising electrical performance. During nail penetration testing, the electronic insulation and high thermal stability of the oxide solid electrolyte layer hinder internal short circuits, effectively preventing heat dissipation within the battery and thus avoiding safety issues such as thermal runaway, combustion, or explosion.

[0043] In some embodiments of this application, the chemical formula of the polyphosphazene compound is: -[-N=P(R1R2)-]- n ,

[0044] R1 includes pyrrolidone;

[0045] R2 is selected from compounds with the following structural formulas:

[0046] M is selected from alkyl, Li, Na or K;

[0047] 500≤n≤20000;

[0048] Polyphosphazene polymers are polymers with phosphorus and nitrogen atoms linked by alternating single and double bonds to form their basic backbone. Each phosphorus atom is attached to two side groups, R1 and R2, with the structural formula -[-N=P(R1R2)-]-n. ​​By selecting appropriate side groups, the material can be endowed with excellent light and heat stability, high and low temperature resistance, biocompatibility, oxidation resistance, solvent resistance, and flame retardancy, among other unique chemical properties. Simultaneously, introducing functional groups onto the two side groups R1 and R2 can achieve functions such as electronic insulation, ion conduction, and flame retardancy, thereby improving the electrical performance and safety performance of batteries.

[0049] In some embodiments of this application, the second adhesive comprises polyvinylidene fluoride.

[0050] In some embodiments of this application, the second solvent includes N-methylpyrrolidone.

[0051] In some embodiments of this application, the chemical formula of the polyphosphazene compound is: -[-N=P(R1R2)-]- n ,

[0052] R1 is selected from compounds with the following structural formulas:

[0053]

[0054] The structure of R2 is shown in the following equation:

[0055] M is selected from CH3, C2H5, C3H7, and C4H9.

[0056] The R1 and R2 groups of the polyphosphazene compound are connected to pyrrolidone and ethyl para-carbamate functional groups. The pyrrolidone functional group has good dispersibility and can improve the dispersion performance of solid electrolytes. The ethyl para-carbamate functional group is similar to the electrolyte and is miscible, which can improve the wetting performance of the positive electrode.

[0057] In some embodiments of this application, the particle size of the oxide solid electrolyte is 100-1000 nm, such as 100 nm, 300 nm, 350 nm, 430 nm, 490 nm, 530 nm, 580 nm, 630 nm, 720 nm, 800 nm, 1000 nm, etc. If the particle size of the oxide solid electrolyte is too small, the slurry will not be easily dispersed and agglomeration will occur; if the particle size of the oxide solid electrolyte is too large, the ion diffusion path will increase, affecting the battery rate and cycle performance.

[0058] In some embodiments of this application, the thickness of the second positive electrode slurry coating is 2-8 μm, such as 2 μm, 5 μm, 7 μm, 8 μm, etc. If the thickness of the second positive electrode slurry coating is too thin, it will not achieve the effect of improving safety; if the thickness of the second positive electrode slurry coating is too thick, it will affect the electrical performance of the battery, such as rate performance, low temperature performance, cycle performance, etc.

[0059] In some embodiments of this application, the current collector includes an aluminum foil current collector.

[0060] In some embodiments of this application, the first positive electrode slurry coating includes a positive electrode active material, a conductive agent, a first binder, and a first solvent.

[0061] In some embodiments of this application, the positive electrode active material includes lithium nickel cobalt manganese oxide.

[0062] In some embodiments of this application, the conductive agent includes conductive carbon black.

[0063] In some embodiments of this application, the first adhesive comprises polyvinylidene fluoride.

[0064] In some embodiments of this application, the first solvent includes N-methylpyrrolidone.

[0065] This application also provides a method for preparing the positive electrode sheet described in the first aspect of this application, comprising the following steps:

[0066] (1) The first positive electrode slurry is coated onto the current collector and dried to obtain the first positive electrode slurry coating;

[0067] (2) The second positive electrode slurry is coated on the surface of the first positive electrode slurry coating, dried, and rolled to obtain the positive electrode sheet.

[0068] In some embodiments of this application, the drying temperature in steps (1) and (2) is independently 80-100°C, such as 80°C, 85°C, 88°C, 90°C, 93°C, 95°C, 100°C, etc., and the drying time is independently 8-12h, such as 8h, 9h, 10h, 12h, etc.

[0069] This application also provides an application of the positive electrode sheet described in the first aspect of this application or the positive electrode sheet obtained by the preparation method described in the second aspect of this application in a semi-solid-state battery.

[0070] The technical solution of this application will be further described below with reference to specific embodiments.

[0071] Example 1

[0072] A method for preparing a semi-solid-state battery includes the following steps:

[0073] S1. Preparation of the first positive electrode slurry coating: Weigh 96 parts by weight of lithium nickel cobalt manganese oxide, 2 parts by weight of polyvinylidene fluoride (PVDF) as the positive electrode binder, and 2 parts by weight of conductive carbon black as the positive electrode conductive agent. First, add PVDF to N-methylpyrrolidone solvent to prepare a slurry. Then, add conductive carbon black to the slurry and stir until uniform. Next, add lithium nickel cobalt manganese oxide to the slurry and stir until uniform. Finally, coat the slurry onto an aluminum foil current collector and dry it at 80°C for 12 hours to prepare a positive electrode sheet with a first positive electrode slurry coating thickness of 144 μm.

[0074] S2. Preparation of the second positive electrode slurry coating: Weigh 90 parts by weight of lithium aluminum titanium phosphate with a particle size of 400 nm, 3.5 parts by weight of polyphosphazene compound and 6.5 parts by weight of binder PVDF. First, add PVDF to N-methylpyrrolidone solvent to make a glue solution. Then add polyphosphazene compound and LATP to the above slurry and stir until uniform. Finally, coat the slurry on the first positive electrode slurry coating prepared in S1 and dry it at 80℃ for 12 h. After rolling and slitting, obtain positive electrode small sheets to obtain a positive electrode sheet with a second positive electrode slurry coating thickness of 5 μm (10 μm on both sides).

[0075] The structural formula of the polyphosphazene compound is shown below:

[0076]

[0077] S3. Preparation of negative electrode sheet: Weigh 85.5 parts graphite negative electrode material, 9.5 parts silicon-carbon negative electrode material, 2.5 parts negative electrode binder polyacrylic acid and 2.5 parts negative electrode conductive agent conductive carbon black according to the mass ratio. First, mix and disperse the conductive carbon black, graphite and silicon-carbon evenly. Then, add polyacrylic acid and deionized water to the above mixture and disperse evenly. Finally, add styrene-butadiene rubber and stir until uniform. After mixing, coat the above slurry on the copper current collector and dry it to prepare the negative electrode sheet. After rolling and slitting, obtain small negative electrode sheets.

[0078] S4. Cell preparation: The positive and negative electrode small pieces are vacuum baked, stacked to form a cell, and then packaged in an aluminum-plastic film.

[0079] S5. Battery preparation: After baking, the battery cells are injected with electrolyte, formed, aged, and tested for capacity to obtain a semi-solid battery.

[0080] Example 2

[0081] The only difference between the preparation method of the semi-solid battery in Example 2 and that in Example 1 is that the particle size of lithium titanium aluminum phosphate used in the preparation process of the semi-solid battery in Example 2 is 100 nm.

[0082] Example 3

[0083] The only difference between the preparation method of the semi-solid battery in Example 3 and that in Example 1 is that the particle size of lithium titanium aluminum phosphate used in the preparation process of the semi-solid battery in Example 3 is 600 nm.

[0084] Example 4

[0085] The only difference between the preparation method of the semi-solid battery in Example 4 and that in Example 1 is that the particle size of lithium titanium aluminum phosphate used in the preparation process of the semi-solid battery in Example 4 is 1000 nm.

[0086] Example 5

[0087] The only difference between the preparation method of the semi-solid battery in Example 5 and that in Example 1 is that the mass ratio of oxide solid electrolyte, polyphosphazene compound and second binder in the preparation process of the semi-solid battery in Example 5 is 85:5:10.

[0088] Example 6

[0089] The only difference between the preparation method of the semi-solid battery in Example 6 and that in Example 1 is that the mass ratio of oxide solid electrolyte, polyphosphazene compound, second binder and second solvent in the preparation process of the semi-solid battery in Example 6 is 95:1.5:3.5.

[0090] Example 7

[0091] The only difference between the preparation method of the semi-solid-state battery in Example 7 and that in Example 1 is that the structural formula of the polyphosphazene compound used in the preparation of the semi-solid-state battery in Example 7 is as follows:

[0092]

[0093] Example 8

[0094] The only difference between the preparation method of the semi-solid-state battery in Example 8 and that in Example 1 is that the structural formula of the polyphosphazene compound used in the preparation of the semi-solid-state battery in Example 8 is as follows:

[0095]

[0096] Example 9

[0097] The only difference between the preparation method of the semi-solid-state battery in Example 9 and that in Example 1 is that the structural formula of the polyphosphazene compound used in the preparation of the semi-solid-state battery in Example 9 is as follows:

[0098]

[0099] Example 10

[0100] The only difference between the preparation method of the semi-solid-state battery in Example 10 and that in Example 1 is that the structural formula of the polyphosphazene compound used in the preparation of the semi-solid-state battery in Example 10 is as follows:

[0101]

[0102] Example 11

[0103] The only difference between the preparation method of the semi-solid battery in Example 11 and that in Example 1 is that the thickness of the second positive electrode slurry coating in the preparation process of the semi-solid battery in Example 11 is 2 μm.

[0104] Example 12

[0105] The only difference between the preparation method of the semi-solid battery in Example 12 and that in Example 1 is that the thickness of the second positive electrode slurry coating in the preparation process of the semi-solid battery in Example 12 is 8 μm.

[0106] Comparative Example 1

[0107] The difference between the preparation method of the semi-solid battery in Comparative Example 1 and Example 1 is that the first positive electrode slurry and the second positive electrode slurry are mixed and coated during the preparation process of the semi-solid battery in Comparative Example 1.

[0108] The specific operating steps include:

[0109] S1. Preparation of the positive electrode sheet: Weigh 2764.8 parts by weight of lithium nickel cobalt manganese oxide, 90 parts of lithium titanium aluminum phosphate with a particle size of 500 nm, 3.5 parts of polyphosphazene compound, 64.1 parts of positive electrode binder polyvinylidene fluoride, and 57.6 parts of positive electrode conductive agent conductive carbon black. First, add polyvinylidene fluoride to N-methylpyrrolidone solvent to prepare a slurry. Then, add the polyphosphazene compound and conductive carbon black to the above slurry and stir until uniform. Then, add lithium nickel cobalt manganese oxide and lithium titanium aluminum phosphate to the above slurry and stir until uniform. Finally, coat the slurry onto an aluminum foil current collector, dry it at 80°C for 12 h, roll it, and prepare a positive electrode sheet with a positive electrode slurry coating thickness of 154 μm.

[0110] The preparation of the negative electrode sheet, the cell, and the battery is the same as in Example 1.

[0111] Comparative Example 2

[0112] The difference between the preparation method of the semi-solid battery in Comparative Example 2 and Example 1 is that the second positive electrode slurry is not coated during the preparation process of the semi-solid battery in Comparative Example 2.

[0113] The specific operating steps include:

[0114] Preparation of the positive electrode sheet: Weigh 96 parts by weight of lithium nickel cobalt manganese oxide, 2 parts by weight of polyvinylidene fluoride (PVDF) as the positive electrode binder, and 2 parts by weight of conductive carbon black as the positive electrode conductive agent. First, add PVDF to N-methylpyrrolidone solvent to prepare a slurry. Then, add conductive carbon black to the slurry and stir until uniform. Next, add lithium nickel cobalt manganese oxide to the slurry and stir until uniform. Finally, coat the slurry onto an aluminum foil current collector and dry it at 80°C for 12 hours to prepare a positive electrode sheet with a coating thickness of 154 μm.

[0115] The preparation of the negative electrode sheet, the cell, and the battery is the same as in Example 1.

[0116] Performance study of the positive electrode sheets described in Examples 1-11 and Comparative Examples 1-2 of this application:

[0117] (1) Capacitive internal resistance: Tested using an AC internal resistance tester;

[0118] (2) Capacity retention rate: Charge at 1C constant current and constant voltage to 4.2V, discharge at 1C constant current to 2.5V, cycle 600 times, and calculate the discharge capacity retention rate. (Equals the discharge capacity of 600 cycles divided by the initial discharge capacity of the 3rd cycle)

[0119] (3) Needle penetration: in accordance with GB31485-2020 Safety requirements and test methods for power batteries for electric vehicles.

[0120] The results are shown in Table 1:

[0121] Table 1

[0122]

[0123]

[0124] As can be seen from Table 1, the semi-solid-state battery described in this application can effectively prevent heat diffusion inside the battery and avoid thermal runaway.

[0125] Comparing Examples 1-4, it can be seen that when the particle size of lithium titanium aluminum phosphate is small, the particles are prone to agglomeration, which deteriorates the processing performance. However, the diffusion distance of lithium ions inside the active material particles is shortened, and the battery performance is improved. In addition, the coating layer with a small particle size is more dense and relatively safer. Conversely, when the particle size of LATP is large, the diffusion path of lithium ions becomes longer, and the battery performance deteriorates. In addition, the coating layer with a large particle size becomes uneven, which is relatively less safe.

[0126] Comparing Examples 1 and 5-6, it can be seen that when the proportion of polyphosphazene compound and binder added is high, the electrical performance will decrease; when the proportion of polyphosphazene compound and binder added is low, the electrical performance will increase, but the safety performance will decrease.

[0127] Comparing Examples 1 and 7-10, it can be seen that when the molecular weight of the M group is small, the material has poor stability and more side reactions, which affects battery performance; when the molecular weight of the M group is large, the material has poor compatibility with the electrolyte, which also affects battery performance.

[0128] Comparing Example 1 and Examples 11-12, it can be seen that when the thickness of the second positive electrode slurry coating increases during the preparation of the semi-solid battery, the safety of the battery will improve, but the electrical performance of the battery will decrease. Taking all factors into consideration, the battery with the thickness of the second positive electrode slurry coating being 5 μm has better performance.

[0129] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A positive electrode plate, characterized in that, It includes a current collector, a first positive electrode slurry coating and a second positive electrode slurry coating sequentially coated on the current collector; The second positive electrode slurry coating comprises the following raw materials in parts by weight: 85-95 parts of oxide solid electrolyte, 1.5-5 parts of polyphosphazene compound, 3.5-10 parts of second binder, and second solvent; The chemical formula of the polyphosphazene compound is: -[-N=P(R1R2)-]- n , R1 includes pyrrolidone; R2 is selected from compounds with the following structural formulas: and M is selected from alkyl, Li, Na or K; 500≤n≤20000； The second adhesive includes polyvinylidene fluoride; The second solvent includes N-methylpyrrolidone.

2. The positive electrode sheet according to claim 1, characterized in that, The oxide solid electrolyte includes one or more of lithium titanium aluminum phosphate, lithium lanthanum titanium oxide, and lithium lanthanum zirconium oxide.

3. The positive electrode sheet according to claim 1, characterized in that, The chemical formula of the polyphosphazene compound is: -[-N=P(R1R2)-]- n , R1 is selected from compounds with the following structural formulas: and ; The structure of R2 is shown in the following equation: M is selected from CH3, C2H5, C3H7, and C4H9.

4. The positive electrode sheet according to claim 1, characterized in that, The particle size of the oxide solid electrolyte is 100-1000 nm.

5. The positive electrode sheet according to claim 1, characterized in that, The thickness of the second positive electrode slurry coating is 2-8 μm.

6. The positive electrode sheet according to claim 1, characterized in that, The current collector includes an aluminum foil current collector; And / or, the first positive electrode slurry coating includes a positive electrode active material, a conductive agent, a first binder, and a first solvent.

7. The positive electrode sheet according to claim 6, characterized in that, The positive electrode active material includes lithium nickel cobalt manganese oxide; And / or, the conductive agent includes conductive carbon black; And / or, the first adhesive comprises polyvinylidene fluoride; And / or, the first solvent includes N-methylpyrrolidone.

8. The method for preparing the positive electrode sheet according to any one of claims 1-7, characterized in that, Includes the following steps: (1) The first positive electrode slurry is coated onto the current collector and dried to obtain the first positive electrode slurry coating; (2) The second positive electrode slurry is coated on the surface of the first positive electrode slurry coating, dried, and rolled to obtain the positive electrode sheet.

9. The application of the positive electrode sheet according to any one of claims 1-7 or the positive electrode sheet obtained by the preparation method according to claim 8 in a semi-solid-state battery.

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