Positive electrode additive, preparation method and positive electrode plate

Abstract

The invention discloses a positive electrode additive, a preparation method and a positive electrode plate, and belongs to the technical field of lithium ion batteries. The positive electrode additive comprises the following raw materials: lithium carbonate, carbon-coated porous ceramic powder and supporting carrier resin in a mass ratio of (1-2): (1.5-3): 100, and the supporting carrier resin is lithiated styrene-acrylic resin. According to the positive electrode additive, lithium carbonate is used as an active overcharge protection substance, carbon-coated porous ceramic powder is used as a functional filler, and supporting carrier resin is used as a continuous phase matrix, so that a stable and efficient heat conduction and electron conduction synergistic network can be formed, and the impedance problem of lithium carbonate can be solved; and the problem of protection lag of lithium carbonate can be solved, and thermal runaway caused by overcharge is prevented. The lithiated styrene-acrylic resin can cooperate with the carbon-coated porous ceramic powder to form a three-dimensional and efficient electron-ion transmission channel, so that the intelligent response characteristic of overcharge protection is improved, and the electrochemical performance of the lithium ion battery is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a positive electrode additive, a preparation method thereof, and a positive electrode sheet. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density and long cycle life. However, as battery energy density continues to increase, safety issues are becoming increasingly prominent, with overcharging being one of the main causes of battery thermal runaway, fire, and even explosion.

[0003] When lithium-ion batteries are overcharged, the positive electrode material suffers irreversible structural damage due to excessive delithiation. At the same time, the electrolyte undergoes violent oxidation and decomposition under high pressure, generating a large amount of heat and gas. Lithium dendrites form on the surface of the negative electrode due to the continuous insertion of lithium, which may puncture the separator and cause an internal short circuit, leading to phenomena such as battery bulging, leakage, combustion, or even explosion. Therefore, effective overcharge protection is crucial for obtaining highly safe lithium-ion batteries.

[0004] Currently, people are establishing electrochemical mechanisms by adding additives to the electrolyte to help absorb excessive current during overcharging, suppress voltage runaway, and achieve battery overcharge protection. However, the overcharge protection agents added to the electrolyte also have limitations. For example, electropolymer additives can affect the performance of lithium batteries, including increasing the internal resistance of the battery and causing battery swelling; redox couple additives are unstable in high-voltage lithium-ion batteries and are difficult to use widely.

[0005] To further overcome the limitations of electrolyte additives, lithium carbonate, as a positive electrode additive, can decompose when a lithium-ion battery is overcharged, the voltage continues to rise and exceeds its decomposition threshold, and gas is produced. The gas causes the internal pressure of the battery to rise, thereby activating the explosion-proof valve and pressure switch at the top of the battery. Then, the charging process is forcibly terminated by venting or mechanically cutting off the circuit, thus effectively preventing the risk of thermal runaway caused by continuous overcharging.

[0006] However, lithium carbonate, as a cathode additive, not only suffers from reduced electronic conductivity and increased internal resistance due to its insulating properties, thus impairing the battery's rate performance, but also exhibits a significant "protection lag" problem. This lag occurs between the onset of overcharging and the triggering of the protection mechanism by lithium carbonate decomposition. Because lithium carbonate decomposition requires a high voltage threshold and temperature, the cathode active material begins to show adverse changes after the voltage exceeds the normal cutoff voltage, before the lithium carbonate triggers the protection mechanism in time. This results in damage to the cathode material during the lag phase, significantly reducing its lifespan. Therefore, developing a cathode additive with faster overcharge response, effective impedance overcoming, and reduced thermal runaway is crucial for improving the safety of lithium-ion batteries. Summary of the Invention

[0007] This invention provides a positive electrode additive, a preparation method, and a positive electrode sheet, which can solve the problems of overcharge thermal runaway and impedance and protection hysteresis of lithium carbonate as a positive electrode additive in the prior art.

[0008] In a first aspect, the present invention provides a positive electrode additive, the raw materials of which include lithium carbonate, carbon-coated porous ceramic powder and support carrier resin in a mass ratio of (1-2):(1.5-3):100. The supporting carrier resin is lithium-ionized styrene-acrylic resin.

[0009] Preferably, the particle size of lithium carbonate is 20–100 nm.

[0010] By adopting the above technical solution, the positive electrode additive of the present invention uses lithium carbonate as an active overcharge protection material, carbon-coated porous ceramic powder as a functional filler, and support carrier resin as a continuous phase matrix to obtain a stable and efficient thermal and electronic conduction synergistic network. This not only solves the impedance problem of lithium carbonate, but also better protects the lithium battery and prevents thermal runaway caused by overcharging.

[0011] Specifically, overcharging causes localized hot spots that accelerate electrolyte decomposition, while the reaction of lithium carbonate in other areas is delayed, resulting in scattered gas production and slow pressure accumulation, leading to protection lag. Carbon-coated porous ceramic powder can be uniformly dispersed in the supporting resin, forming a highly efficient heat conduction path that runs through the cathode additive particles. When the overcharge reaction begins, the heat generated by lithium carbonate decomposition can be rapidly conducted from the reaction site and dispersed to other locations by the heat-conducting network. Furthermore, by suppressing the sharp rise in local temperature, it ensures that the lithium carbonate decomposition reaction is not randomly triggered by uncontrollable thermal runaway, resulting in a more synchronous and concentrated decomposition reaction. This significantly shortens the effective gas production time, allowing for the generation of large quantities of gas in a shorter time, making the protection response more timely and reliable.

[0012] Moreover, due to the insulating properties of lithium carbonate, it affects the electronic conduction path of the positive electrode active material. Carbon-coated porous ceramic powder and lithium carbonate are uniformly dispersed in the resin at the same time. The carbon coating layer can form a three-dimensional electron transport network in the resin matrix, providing a good electronic contact interface. Electrons can directly reach the reaction sites on the surface of the positive electrode active material, thereby greatly reducing the charge transfer impedance and reducing the internal resistance of the lithium battery.

[0013] The supporting resin, as a continuous phase, firmly binds the carbon-coated porous ceramic powder and lithium carbonate together. This not only improves the uniformity and stability of ion distribution, forming a continuous network, but also significantly enhances the overall thermal stability and maintains the structural integrity of the cathode additive.

[0014] Meanwhile, the supporting resin of this application is lithium styrene-acrylic resin, which can form a strong interfacial interaction with carbon-coated porous ceramic powder and lithium carbonate, so that the particles are anchored and uniformly dispersed in the resin matrix, increasing the reaction interface of lithium carbonate, preventing the formation of agglomeration, and enabling the decomposition reaction to occur synchronously and rapidly during overcharging, thus shortening the voltage trigger delay time.

[0015] On the other hand, the lithiated resin also provides lithium-ion transport channels. Together with the electron transport channels provided by the carbon coating layer of the carbon-coated porous ceramic powder, an electron-ion conductive network can be constructed around lithium carbonate. When overcharging occurs, electrons and lithium ions can be efficiently and with low resistance transported to each active site of lithium carbonate through the carbon network and the resin network, respectively, ensuring that it undergoes rapid electrochemical decomposition. This solves the high impedance problem caused by poor charge transport and does not affect the rate performance of the lithium-ion battery itself.

[0016] Preferably, the raw materials for carbon-coated porous ceramic powder include porous ceramic powder and carbon source in a mass ratio of 1:(0.4 to 0.6).

[0017] Preferably, the porous ceramic powder includes one or more of porous alumina, porous boron nitride, and porous aluminum nitride; the particle size of the porous ceramic powder is 200-500 nm.

[0018] Preferably, the carbon source includes one or more combinations of glucose, sucrose, fructose, citric acid, and sodium citrate.

[0019] Preferably, the carbon-coated porous ceramic powder is prepared by the following method: Weigh the porous ceramic powder and carbon source according to the mass ratio and mix them evenly. Raise the temperature to 180-185℃ to carry out a hydrothermal reaction. After reacting for 20-24 hours, carbon-coated porous ceramic powder is obtained.

[0020] By adopting the above technical solution, under high temperature conditions, the carbon source undergoes hydrolysis, dehydration, polymerization and carbonization, and is adsorbed on the surface of porous ceramic powder. The carbon-coated porous ceramic powder obtained through hydrothermal reaction can avoid the collapse of the pores of the porous ceramic powder caused by high-temperature calcination. Moreover, the generated carbon layer is dense and uniform, and the surface contains abundant oxygen-containing functional groups, thereby enhancing the interfacial bonding force between the carbon layer and the supporting resin.

[0021] Introducing carbon-coated porous ceramic powder into the cathode additive has several advantages. First, the carbon layer generated in situ on the surface establishes a continuous electronic conduction network inside the additive particles. When overcharging occurs, electrons can be transferred from the cathode current collector through the conductive agent and via the carbon layer to the reaction sites on the surface of the cathode active material with low resistance, reducing charge transfer impedance. This not only solves the problem of high internal resistance caused by lithium carbonate, but also ensures that lithium carbonate can decompose rapidly and synchronously when overcharging occurs.

[0022] On the other hand, porous ceramic powder itself has good thermal conductivity, and the carbon layer coating can further improve thermal conductivity. It can not only quickly dissipate the heat of reaction generated by the decomposition of lithium carbonate, but also prevent local overheating caused by overcharging, thereby inhibiting the violent decomposition reaction of the electrolyte, ensuring that the decomposition process of lithium carbonate is controllable and concentrated, shortening the time to trigger overcharge protection, and also improving the stability of the battery before the overcharge protection is triggered.

[0023] Furthermore, the carbon-coated porous ceramic powder of this invention has a porous structure, and its large specific surface area can improve reactivity, providing reaction sites and space for subsequent resin-based composite filling, thus helping to form a more structurally stable system. Its interconnected channels can also provide an escape path for gases generated by the decomposition of lithium carbonate; the gases can collect along the channels, accelerating the accumulation of internal pressure and reducing trigger time.

[0024] Preferably, the raw materials for lithium-ionized styrene-acrylic resin include styrene-acrylic resin and a lithium source in a mass ratio of 100:(0.03-0.04); the lithium source includes one or a combination of lithium hydroxide and lithium acetate.

[0025] Preferably, the lithium-ionized styrene-acrylic resin is prepared according to the following method: Styrene-acrylic resin is added to a solvent and stirred to dissolve, resulting in a resin solution. A lithium source is dissolved in deionized water to obtain a lithium ion aqueous solution with a concentration of 2-5%. The resin solution is added to the lithium ion aqueous solution, the temperature is raised to 70-80℃, and the reaction is stirred for 1-2 hours. Finally, the solvent is removed by rotary evaporation to obtain lithium-ionized styrene-acrylic resin.

[0026] More preferably, the solvent includes N-methylpyrrolidone.

[0027] By adopting the above technical solution, the molecular chain of styrene-acrylic resin contains a large number of carboxyl groups, which can undergo a neutralization reaction with the lithium source, thereby realizing the lithiation of styrene-acrylic resin.

[0028] This invention selects lithium-ion styrene-acrylic resin as the support carrier resin for the cathode additive. Its styrene segments can provide a rigid hydrophobic framework, form physical cross-linking points, and improve the mechanical strength and dimensional stability of the cathode additive. The polar groups in the contained acrylic segments can provide reactive active sites, improve the interfacial strength with carbon-coated porous ceramic powder and lithium carbonate, and thus obtain a cathode additive with good continuity.

[0029] After lithiation, the resin can synergistically form a three-dimensional, highly efficient electron-ion transport channel with the electronic conductivity network provided by the carbon-coated porous ceramic powder, which can also improve the electron and ion conduction rate of the cathode material. Moreover, in the early stage of overcharging, it can temporarily release and provide some lithium ions to maintain the balance of charge at the cathode interface and prevent local structural collapse and strong oxidation reactions.

[0030] Secondly, the present invention provides a method for preparing a positive electrode additive, which includes the following process steps: S1. Lithium carbonate and carbon-coated porous ceramic powder are ultrasonically dispersed in an alcohol solvent to obtain a suspension; S2. Lithium-ionized styrene-acrylic resin is added to an alcohol solvent and stirred to dissolve. Then it is added to a suspension, the temperature is raised to 45-50°C, and the mixture is stirred for 1-2 hours. Then a film-forming aid is added, and the mixture is stirred for another 0.5-1 hour. Finally, the mixture is dried and ground to obtain the final product.

[0031] More preferably, the alcohol solvent includes any one of methanol, ethanol, and isopropanol.

[0032] More preferably, the film-forming aid includes any one of alcohol ester dodecyl, propylene glycol phenyl ether, ethylene glycol butyl ether, and diethylene glycol butyl ether; the amount of film-forming aid added is 5 to 10% of the mass of the support carrier resin.

[0033] By adopting the above technical solution, carbon-coated porous ceramic powder and lithium carbonate are first dispersed in an alcohol solvent to reduce agglomeration. Then, lithium-coated styrene-acrylic resin is added and adsorbed on the surface of the suspended particles. The particles are bound together through hydrogen bonds and intermolecular forces. Finally, the particles are coated, forming a continuous phase around the particles. This improves the continuity between the carbon-coated porous ceramic powder and lithium carbonate, thereby improving the overall performance.

[0034] The cathode additive prepared by the above method constructs an electron-ion dual-channel transport network. The carbon coating layer provides the electron transport path, and the lithium-ion transport path is provided by the lithium-ion styrene-acrylic resin, thereby reducing impedance and preventing the problem of increased internal resistance caused by lithium carbonate affecting battery performance.

[0035] Furthermore, the cathode additive can achieve uniform distribution of lithium carbonate through resin and uniform heat conduction through carbon-coated porous ceramic powder, thus ensuring the synchronous and rapid decomposition reaction. Its porous structure also helps the generated gas to accumulate quickly, accelerating the triggering of overcharge protection. On the other hand, it can form a good thermal buffer, suppressing local hot spots, improving the stability of the material, and reducing the potential problems of thermal runaway or unstable active material structure during overcharging.

[0036] By adding positive electrode additives, the intelligent response characteristics of lithium batteries to overcharge protection can be improved. This allows for rapid, concentrated, and precise triggering of the safety device's protective behavior, thereby enhancing the overcharge safety of lithium-ion batteries without affecting the performance of the positive electrode material. It can also improve the electrochemical performance of lithium-ion batteries.

[0037] Thirdly, the present invention provides a positive electrode sheet, comprising a positive current collector and a positive active material layer, wherein the positive active material layer comprises a positive active material, the aforementioned positive electrode additive, a conductive agent and a binder; The amount of positive electrode additive added is 4 to 8% of the mass of the positive electrode active material.

[0038] More preferably, the positive electrode active material includes any one of lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium cobalt oxide, lithium cobalt phosphate, lithium manganese oxide, lithium nickel vanadium oxide, and lithium cobalt sulfate fluoride.

[0039] More preferably, the conductive agent includes any one of graphite, carbon black, carbon nanotubes, graphene, and acetylene black.

[0040] More preferably, the adhesive includes any one of polytetrafluoroethylene, polyvinyl alcohol, polyvinylidene fluoride, polyimide, polyacrylic acid, polyacrylonitrile, and sodium carboxymethyl cellulose.

[0041] More preferably, the mass ratio of the positive electrode active material, the positive electrode additive, the conductive agent and the binder is 100:(4-8):(1-10):(2-5).

[0042] The beneficial effects of this invention are: 1. The positive electrode additive obtained by the present invention uses lithium carbonate as an active overcharge protection material, carbon-coated porous ceramic powder as a functional filler, and support carrier resin as a continuous phase matrix, which can form a stable and efficient thermal and electronic conduction synergistic network. It can not only solve the impedance problem of lithium carbonate, but also better protect the lithium battery and prevent thermal runaway caused by overcharging.

[0043] 2. The carbon-coated porous ceramic powder in the cathode additive of this invention establishes a continuous electron conduction network within its carbon coating layer, reducing charge transfer impedance. This not only solves the problem of high internal resistance caused by lithium carbonate but also ensures rapid and synchronous decomposition of lithium carbonate during overcharging. Furthermore, the porous ceramic powder itself has good thermal conductivity, enabling rapid dissipation of the reaction heat generated by lithium carbonate decomposition and preventing localized overheating caused by overcharging. Its porous structure provides an escape path for the gas generated by lithium carbonate decomposition, reducing the trigger time of overcharge protection.

[0044] 3. The supporting resin in the cathode additive of this invention is lithium-modified styrene-acrylic resin, which can improve the continuity of the additive. After lithiation, it can synergistically coat porous ceramic powder with carbon to form a three-dimensional and efficient electron-ion transport channel. The final composite cathode additive, with its continuous phase support, can improve the overall integrity, enhance the intelligent response characteristics of lithium batteries to overcharge protection, improve the overcharge safety of lithium-ion batteries, and also improve the electrochemical performance of lithium-ion batteries. Detailed Implementation

[0045] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0046] Preparation Example 1

[0047] Preparation Example 1-1: A carbon-coated porous ceramic powder was prepared according to the following method: Weigh out porous ceramic powder (porous alumina with an average particle size of 200 nm) and carbon source (glucose) at a mass ratio of 1:0.5 and mix them evenly. Raise the temperature to 180℃ for hydrothermal reaction. After 24 hours of reaction, carbon-coated porous ceramic powder is obtained.

[0048] Preparation Examples 1-2: A carbon-coated porous ceramic powder was prepared according to the following method: Weigh out porous ceramic powder (boron nitride with an average particle size of 320 nm) and carbon source (sucrose) at a mass ratio of 1:0.4 and mix them evenly. Raise the temperature to 185℃ for hydrothermal reaction. After 24 hours of reaction, carbon-coated porous ceramic powder is obtained.

[0049] Preparation Examples 1-3: A carbon-coated porous ceramic powder, which differs from Preparation Example 1-1 only in that an equal amount of nano-alumina powder is used to replace the porous alumina.

[0050] Preparation Example 2

[0051] Preparation Example 2-1: A lithium-ionized styrene-acrylic resin was prepared according to the following method: 100 parts of styrene-acrylic resin (average molecular weight 7000) were added to N-methylpyrrolidone and stirred to dissolve to obtain a resin solution; 0.04 parts of lithium hydroxide were dissolved in deionized water to obtain a 3% lithium ion aqueous solution; the resin solution was added to the lithium ion aqueous solution, the temperature was raised to 70°C, and the reaction was stirred for 1 hour. Finally, the solvent was removed by rotary evaporation to obtain lithium styrene-acrylic resin.

[0052] Preparation Example 2-2 is a lithium-ionized styrene-acrylic resin, which differs from Preparation Example 2-1 only in that the amount of lithium hydroxide added is 0.1 parts.

[0053] Example

[0054] Example 1: A positive electrode additive was prepared according to the following method: S1. 1g of lithium carbonate (average particle size of 50nm) and 3g of carbon-coated porous ceramic powder prepared in Preparation Example 1-1 were ultrasonically dispersed in 100mL of ethanol to obtain a suspension. S2. Add 100g of lithium styrene-acrylic resin to 500mL of ethanol and stir to dissolve. Then add the solution to the suspension, raise the temperature to 45℃, stir and react for 2h. Then add 6g of film-forming aid alcohol ester dodecyl and continue stirring and reacting for 1h. Finally, dry and grind to obtain the final product.

[0055] A positive electrode sheet is prepared according to the following method: Lithium iron phosphate, a positive electrode active material with a particle size of 5 μm, the positive electrode additive prepared above, the conductive agent acetylene black, and the binder polyvinylidene fluoride are mixed evenly in the solvent N-methylpyrrolidone to obtain a positive electrode slurry, wherein the mass ratio of lithium iron phosphate, positive electrode additive, conductive agent and binder is 100:6:1.5:2. The positive electrode slurry is coated onto an aluminum foil current collector, vacuum dried at 120°C for 24 hours, and finally pressed and rolled to obtain the positive electrode sheet.

[0056] Example 2, a positive electrode additive, differs from Example 1 only in that the amount of lithium carbonate added is 2g, and the amount of carbon-coated porous ceramic powder prepared in Example 1-1 is 1.5g.

[0057] Example 3, a positive electrode additive, differs from Example 1 only in that an equal amount of carbon-coated porous ceramic powder prepared in Preparation Examples 1-2 is used to replace the carbon-coated porous ceramic powder prepared in Preparation Example 1-1.

[0058] Comparative Example

[0059] Comparative Example 1, a positive electrode additive, differs from Example 1 only in that the amount of lithium carbonate added is 2g.

[0060] Comparative Example 2, a positive electrode additive, differs from Example 1 only in that an equal amount of the lithium styrene-acrylic resin prepared in Preparation Example 2-2 is used instead of the lithium styrene-acrylic resin prepared in Preparation Example 2-1.

[0061] Comparative Example 3, a positive electrode additive, differs from Example 1 only in that an equal amount of porous alumina (average particle size of 200 nm) is used to replace the carbon-coated porous ceramic powder prepared in Preparation Example 1-1.

[0062] Comparative Example 4, a positive electrode additive, differs from Example 1 only in that an equal amount of styrene-acrylic resin is used to replace the lithium-ionized styrene-acrylic resin prepared in Preparation Example 2-1.

[0063] Comparative Example 5, a positive electrode additive, differs from Example 1 only in that an equal amount of carbon-coated porous ceramic powder prepared in Preparation Examples 1-3 is used instead of carbon-coated porous ceramic powder prepared in Preparation Examples 1-1.

[0064] Comparative Example 6 is a positive electrode additive, which differs from Example 1 only in that the carbon-coated porous ceramic powder prepared in Preparation Example 1-1 is not added.

[0065] Comparative Example 7, a positive electrode additive, was prepared according to the following method: The mixture is prepared by uniformly mixing 1g of lithium carbonate (average particle size of 50nm) and 3g of carbon-coated porous ceramic powder prepared in Example 1-1.

[0066] Performance testing

[0067] Sample preparation: Using lithium metal sheet as negative electrode, polypropylene porous membrane as separator, positive electrode sheet obtained in the examples and comparative examples as positive electrode, and a mixed solution of ethylene carbonate and dimethyl carbonate with a volume ratio of 1 mol / L LiPF6 as electrolyte, the battery was assembled under an argon atmosphere to obtain the battery sample.

[0068] Performance testing: 1. Electrochemical performance test: Set the charging current density to 0.1C, charge to the cutoff voltage of 4.6V, and test the first charge specific capacity of the battery sample.

[0069] 2. Safety performance test: Charge at 1C rate until the current blocking device of the battery sample takes effect, and obtain the battery overcharge failure voltage and overcharge failure SOC when the overcharge is terminated.

[0070] The results of the above experiments are shown in Table 1.

[0071] Table 1 Performance test results

[0072] Note: In Table 1, " / " indicates that the battery is damaged and specific data cannot be tested.

[0073] According to Table 1, combined with Example 1 and Comparative Example 1, it can be seen that the specific capacity of the first charge of Comparative Example 1 decreased. The reason may be that the excessive active material caused the decomposition reaction to occur prematurely during the lithium battery charging process, and the protection was too sensitive, thus sacrificing the normal usable capacity of the battery.

[0074] Combining Example 1 and Comparative Example 2, it can be seen that the performance of Comparative Example 2 is lower than that of Example 1. The reason may be that the lithium styrene-acrylic resin in Comparative Example 2 contains an excessive amount of lithium source, which will lead to a decrease in the number of active groups in the resin and damage to the structure. This will not only affect the interfacial bonding force between the resin and lithium carbonate and carbon-coated porous ceramic powder, but also affect the ion conduction function, resulting in a slower response.

[0075] Combining Example 1 and Comparative Example 3, it can be seen that the performance of Comparative Example 3 is lower than that of Example 1. The reason may be that the porous ceramic powder in Comparative Example 3 has not undergone carbon coating treatment, which leads to an increase in charge transfer resistance and a decrease in safety after the protection reaction.

[0076] Combining Example 1 and Comparative Example 4, it can be seen that the performance of Comparative Example 4 is lower than that of Example 1. The reason may be that the styrene-acrylic resin in Comparative Example 4 has not undergone lithium treatment, which will lead to ion conduction blockage and reaction lag.

[0077] Combining Example 1 and Comparative Example 5, it can be seen that the performance of Comparative Example 5 is lower than that of Example 1. The reason may be that the carbon-coated ceramic powder in Comparative Example 5 does not have a porous structure, which will cause the gas to be unable to accumulate quickly, the pressure to accumulate slowly, and the protection to be triggered slowly.

[0078] Based on Examples 1, 6, and 7, it can be seen that the performance of Comparative Examples 6 and 7 is lower than that of Example 1. This may be because Comparative Example 6 did not include carbon-coated porous ceramic powder, which significantly reduces thermal conductivity and electron transport, resulting in a substantial performance decrease. Comparative Example 7, lacking a supporting resin, suffers from difficulty in dispersing active particles such as lithium carbonate, leading to agglomeration, localized thermal runaway, and protection failure.

[0079] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A positive electrode additive, characterized in that, The raw materials for the positive electrode additive include lithium carbonate, carbon-coated porous ceramic powder, and support carrier resin in a mass ratio of (1-2):(1.5-3):

100. The supporting carrier resin is lithium styrene-acrylic resin.

2. The positive electrode additive according to claim 1, characterized in that, The raw materials for the carbon-coated porous ceramic powder include porous ceramic powder and carbon source in a mass ratio of 1:(0.4 to 0.6).

3. The positive electrode additive according to claim 2, characterized in that, The porous ceramic powder includes one or more of porous alumina, porous boron nitride, and porous aluminum nitride; the particle size of the porous ceramic powder is 200-500 nm.

4. The positive electrode additive according to claim 2, characterized in that, The carbon source includes one or more combinations of glucose, sucrose, fructose, citric acid, and sodium citrate.

5. The positive electrode additive according to claim 2, characterized in that, The carbon-coated porous ceramic powder was prepared by the following method: Weigh the porous ceramic powder and carbon source according to the mass ratio and mix them evenly. Raise the temperature to 180-185℃ to carry out a hydrothermal reaction. After reacting for 20-24 hours, carbon-coated porous ceramic powder is obtained.

6. The positive electrode additive according to claim 1, characterized in that, The raw materials for the lithium-ionized styrene-acrylic resin include styrene-acrylic resin and a lithium source in a mass ratio of 100:(0.03-0.04); the lithium source includes one or a combination of lithium hydroxide and lithium acetate.

7. The positive electrode additive according to claim 6, characterized in that, The lithium-ionized styrene-acrylic resin was prepared according to the following method: Styrene-acrylic resin is added to a solvent and stirred to dissolve, resulting in a resin solution. A lithium source is dissolved in deionized water to obtain a lithium ion aqueous solution with a concentration of 2-5%. The resin solution is added to the lithium ion aqueous solution, the temperature is raised to 70-80℃, and the reaction is stirred for 1-2 hours. Finally, the solvent is removed by rotary evaporation to obtain lithium-ionized styrene-acrylic resin.

8. The positive electrode additive according to claim 1, characterized in that, The lithium carbonate has a particle size of 20–100 nm.

9. A method for preparing a positive electrode additive, used to prepare the positive electrode additive according to any one of claims 1 to 8, characterized in that, The process includes the following steps: S1. Lithium carbonate and carbon-coated porous ceramic powder are ultrasonically dispersed in an alcohol solvent to obtain a suspension; S2. Lithium-ionized styrene-acrylic resin is added to an alcohol solvent and stirred to dissolve. Then it is added to a suspension, the temperature is raised to 45-50°C, and the mixture is stirred for 1-2 hours. Then a film-forming aid is added, and the mixture is stirred for another 0.5-1 hour. Finally, the mixture is dried and ground to obtain the final product.

10. A positive electrode sheet, comprising a positive current collector and a positive active material layer, characterized in that, The positive electrode active material layer includes a positive electrode active material, a positive electrode additive according to any one of claims 1 to 8, a conductive agent, and a binder; The amount of the positive electrode additive added is 4 to 8% of the mass of the positive electrode active material.

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