Positive pole piece, secondary battery and electric equipment

Abstract

The invention provides a positive pole piece, a secondary battery and electric equipment. The positive pole piece provided by the invention comprises a positive current collector and a positive active layer arranged on the surface of one side or two sides of the positive current collector, the positive electrode active layer comprises a positive electrode active material and a pore forming agent; the pore forming agent comprises lithium supplementing particles and a coating layer coating the surfaces of the lithium supplementing particles, the coating layer comprises a catalyst and a gas adsorbent, and the catalyst is selected from one or more of Fe, Cu, Ni and metal oxides thereof. According to the positive pole piece disclosed by the invention, the pore-forming agent with a special structure is added into the positive active layer, so that the battery has excellent energy density, initial efficiency, cycle performance and quick charge performance and relatively low gas production rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a positive electrode sheet, a secondary battery and an electrical device. Background Art

[0002] With the rapid development of the new energy field and the improvement of people's living standards, the requirements for the battery life and service life of digital devices and electric vehicles are becoming higher and higher. Therefore, improving the energy density and cycle life of lithium-ion batteries is a research hotspot in the battery field.

[0003] From the perspective of technology and R&D costs, increasing the compaction density of the electrode is one of the shortcuts to improve the energy density of lithium-ion batteries. However, electrodes with high compaction density are not conducive to the infiltration of the electrolyte and the diffusion of lithium ions, which in turn leads to the deterioration of battery cycle performance and fast charging performance.

[0004] Therefore, how to make the battery have high energy density while also having excellent cycle performance and fast charging performance is a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] The present invention provides a positive electrode plate, a secondary battery, and an electrical device. The positive electrode plate of the present invention adds a pore-forming agent with a special structure to the positive electrode active layer. After formation, the pore-forming agent can not only replenish lithium for the battery, but also absorb the gas generated in the formation stage, improving the battery and the initial efficiency and gas production. In addition, after formation, the pore-forming agent will also form a partially hollow structure in situ and the coating layer has a multi-porous structure, providing sufficient pore space for the migration and diffusion of lithium ions and the infiltration of electrolyte, so that the battery has excellent cycle performance and fast charging performance. Therefore, the secondary battery including the positive electrode plate has excellent energy density, initial efficiency, cycle performance, fast charging performance and low gas production.

[0006] A first aspect of the present invention provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode active layer disposed on one or both sides of the positive electrode current collector; the positive electrode active layer comprises a positive electrode active material and a pore-forming agent;

[0007] The pore-forming agent includes lithium-supplementing particles and a coating layer coated on the surface of the lithium-supplementing particles. The coating layer includes a catalyst and a gas adsorbent. The catalyst is selected from one or more of Fe, Cu, Ni and metal oxides thereof.

[0008] The positive electrode sheet as described above, wherein the gas adsorbent includes one or more of sulfites, ferrous salts, and aluminum oxide.

[0009] The positive electrode sheet as described above, wherein the lithium supplement particles include one or more of Li2O, Li2O2, Li2NiO2, Li5FeO4 and Li2CO3.

[0010] The positive electrode sheet as described above, wherein the D50 particle size of the lithium supplement particles is 5 to 20 μm, preferably 10 to 15 μm;

[0011] And / or, the coating layer has a thickness of 100 to 300 nm, preferably 150 to 250 nm.

[0012] In the positive electrode sheet as described above, the mass ratio of the gas adsorbent to the catalyst is (10-30):1, preferably (15-25):1.

[0013] In the positive electrode sheet as described above, the mass content of the pore former is 1% to 3%, preferably 1.5% to 2.5%, based on the total mass of the positive electrode active layer.

[0014] The positive electrode sheet as described above, wherein the positive electrode active material includes lithium manganese iron phosphate.

[0015] The positive electrode sheet as described above, wherein the pore-forming agent is prepared by a method comprising the following steps:

[0016] A catalyst and a gas adsorbent are added to a dispersion of lithium supplement particles, and the mixture is heat treated at 50-80° C. for 10-15 hours to obtain a pore-forming agent precursor; and the pore-forming agent precursor is calcined at 600-800° C. for 10-16 hours to obtain the pore-forming agent.

[0017] A second aspect of the present invention provides a secondary battery comprising the positive electrode sheet described above.

[0018] A third aspect of the present invention provides an electrical device comprising the secondary battery described above.

[0019] The implementation of the present invention has at least the following beneficial effects:

[0020] 1) The active layer of the positive electrode plate of the present invention includes a pore-forming agent, which includes lithium-supplementing particles and a coating layer coated on the surface of the lithium-supplementing particles. The coating layer includes a catalyst and a gas adsorbent. During the battery formation stage, the catalyst can be free in the core and fully contact the lithium-supplementing particles, thereby reducing the decomposition voltage of the lithium-supplementing particles and causing the lithium-supplementing particles to decompose at a lower voltage. This can avoid oxidation and gas production of the electrolyte under high voltage, and the lithium-supplementing particles produce irreversible active lithium after in-situ decomposition to play a lithium-supplementing role, thereby increasing the initial efficiency of the battery. At the same time, after the decomposition of the lithium-supplementing particles, no residue or only some inactive substances will remain, which reduces the volume and forms pores in situ. In addition, the catalyst is freed from the coating layer during the catalytic decomposition of the lithium-supplementing particles, so that the decomposed pore-forming agent has a partially hollow structure with multiple pores, which can provide sufficient lithium ion migration and diffusion channels and electrolyte infiltration space, thereby improving the battery's cycle performance and fast charging performance. In addition, the gas adsorbent in the coating layer can adsorb the gases produced by the oxidation and decomposition of lithium-supplemented particles and the electrolyte, preventing the battery from producing gas and expanding, and further improving the battery's cycle performance.

[0021] 2) The secondary battery provided by the present invention, because it includes the above-mentioned positive electrode plate, can have excellent energy density, first efficiency, cycle performance, fast charging performance and low gas production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet after formation according to one embodiment of the present invention;

[0023] Figure 2 Schematic diagram of the structure of the pore-forming agent after formation according to one embodiment of the present invention.

[0024] Description of reference numerals:

[0025] 1-positive electrode current collector; 2-positive electrode active layer; 3-pore-forming agent after formation; 31-coating layer; 32-core. DETAILED DESCRIPTION

[0026] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0027] A first aspect of the present invention provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode active layer disposed on one or both sides of the positive electrode current collector; the positive electrode active layer comprises a positive electrode active material and a pore-forming agent;

[0028] The pore-forming agent includes lithium-supplementing particles and a coating layer coated on the surface of the lithium-supplementing particles. The coating layer includes a catalyst and a gas adsorbent. The catalyst is selected from one or more of Fe, Cu, Ni and metal oxides thereof.

[0029] Among them, Fe, Cu, Ni and their metal oxides refer to that the type of catalyst can be selected from one or more of Fe, Cu, Ni and metal oxides of Fe, Cu and Ni.

[0030] The present invention adds the above-mentioned pore-forming agent to the positive electrode sheet. During the battery formation stage, the Fe, Cu, Ni and their metal oxides and other catalysts located in the coating layer are freed in the core of the pore-forming agent under the infiltration of the electrolyte and fully contact the lithium-replenishing particles. This can reduce the decomposition voltage of the lithium-replenishing particles, allowing the lithium-replenishing particles to decompose at a lower voltage, and can avoid the oxidation and gas production of the electrolyte under high voltage. After the lithium-replenishing particles decompose in situ, they produce irreversible active lithium to replenish lithium, thereby increasing the initial efficiency of the battery. At the same time, after the lithium-replenishing particles decompose, there will be no residue or only some inactive substances remaining, which reduces the volume. At the same time, gases such as oxygen, nitrogen or carbon dioxide will be generated, which can form pores in situ. In addition, the catalyst is freed from the coating layer during the catalytic decomposition of the lithium-replenishing particles, so that the decomposed pore-forming agent has a partially hollow structure with multiple pores, which can provide a migration channel for lithium ions and an infiltration space for the electrolyte, thereby improving the battery's cycle performance and fast charging performance.

[0031] Figure 1 FIG. 1 is a schematic diagram of the structure of the positive electrode sheet after formation according to an embodiment of the present invention. Figure 1 As shown, the formed positive electrode sheet includes a positive electrode current collector 1 and a positive electrode active layer 2 disposed on one side of the positive electrode current collector, and the positive electrode active layer 2 includes a formed pore-forming agent 3. Figure 2 FIG. 1 is a schematic diagram of the structure of the pore-forming agent after chemical formation according to an embodiment of the present invention. Figure 2 As shown, the pore-forming agent after formation includes a core 32 and a coating layer 31, wherein the core 32 is a partially hollow structure, and its core part is the inactive substance produced after the decomposition of the lithium-supplementing particles. The coating layer 31 is a multi-porous discontinuous coating layer, and lithium ions can migrate and diffuse along the path of the blue line, thereby improving the fast charging performance of the battery.

[0032] In addition, the gas adsorbent in the coating layer can adsorb the gases produced by the oxidation and decomposition of lithium-supplemented particles and the electrolyte, preventing the battery from producing gas and expanding, and further improving the battery's cycle performance.

[0033] In summary, the positive electrode plate of the present invention, by adding a pore-forming agent with a specific composition and structure, can have a high compaction density so that the battery has a high energy density, while also having a high first efficiency and excellent cycle performance and fast charging performance.

[0034] In a preferred embodiment, the gas adsorbent includes one or more of sulfites, ferrous salts, and aluminum oxide. Sulfites and ferrous salts have a reducing function, fully reducing the oxidizing gases generated by the decomposition of the lithium-supplementing particles and the electrolyte, preventing these gases from oxidizing and decomposing the positive electrode material, further improving the battery's cycle performance. Aluminum oxide has an adsorption function, adsorbing gases such as carbon dioxide and oxygen generated by the decomposition of the lithium-supplementing particles and the electrolyte, thereby preventing these gases from adversely affecting the battery.

[0035] The present invention does not particularly limit the type of lithium-supplementing particles, which can be selected from conventional positive electrode lithium-supplementing materials in the art, including but not limited to one or more of Li2O, Li2O2, Li2NiO2, Li5FeO4 and Li2CO3, preferably Li2O, which has high irreversible capacity, good lithium-supplementing effect, and less inactive substances produced after complete decomposition.

[0036] In a preferred embodiment, the D50 particle size of the lithium-supplementing particles is 5 to 20 μm, preferably 10 to 15 μm. Exemplarily, the D50 particle size of the lithium-supplementing particles is 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, or a range consisting of any two of the above values. When the D50 particle size of the lithium-supplementing particles is less than 5 μm, its specific surface area is too large, making it difficult for the pore-forming agent to be evenly dispersed, and the pore-forming particle size is reduced, which is not conducive to the mass transfer of lithium-ion batteries; when the D50 particle size of the lithium-supplementing particles is greater than 20 μm, it is difficult for the catalyst to approach the center of the lithium-supplementing particles within the limited formation time, resulting in incomplete decomposition and poor lithium-supplementing effect.

[0037] In a preferred embodiment, the thickness of the coating layer is 100 to 300 nm, preferably 150 to 250 nm. Exemplarily, the thickness of the coating layer can be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, or a range consisting of any two of the above values. If the thickness of the coating layer is too large, it is not conducive to improving the energy density of the battery. If the thickness of the coating layer is too small, it will lead to uneven coating, making it difficult to fully isolate the lithium-supplementing particles from moisture and air, resulting in poor air stability and easy reaction to generate lithium hydroxide, lithium carbonate, etc., resulting in an increase in the residual alkali content on the surface and increased difficulty in slurry coating.

[0038] In a preferred embodiment, the mass ratio of the gas adsorbent to the catalyst is (10-30):1, preferably (15-25):1. For example, it can be 10:1, 15:1, 20:1, 25:1, 30:1, or a range consisting of any two of the above ratios.

[0039] In a preferred embodiment, based on the total mass of the positive electrode active layer, the mass content of the pore former is 1% to 3%, preferably 1.5% to 2.5%. Exemplarily, the mass content of the pore former can be 1%, 1.5%, 2.0%, 2.5%, 3% or a range consisting of any two ratios of the above. It can be understood that the higher the content of the pore former, the more conducive it is to produce more pores after the battery is formed, which helps the migration and transmission of lithium ions, but the higher the content of the pore former, the more it will inevitably affect the energy density of the battery. Controlling the mass content of the pore former within the above range can enable the battery to have more balanced energy density, cycle performance and fast charging performance.

[0040] The present invention does not specifically limit the type of positive electrode active material, which can be selected from the positive electrode active materials commonly used in the art, including but not limited to lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, lithium iron phosphate, lithium nickel manganese oxide, lithium iron manganese phosphate, lithium rich manganese based material one or more. The positive electrode plate of the present invention is more suitable for a positive electrode material system including lithium iron manganese phosphate. Lithium iron manganese phosphate positive electrode material has improved energy density on the basis of lithium iron phosphate material and has received widespread attention. It has higher safety than ternary materials, but its energy density is still lower than that of ternary materials. It is necessary to increase the coating area density, increase the compaction density of the positive electrode active layer and the thickness of the plate to increase the energy density. However, the high compaction density and large thickness lead to further increase in the migration path and migration resistance of lithium ions. At this time, matching with a pore-forming agent can generate more pores in the plate during the formation stage, improve the wettability of the electrolyte, reduce the migration resistance of lithium ions, and make the battery of lithium iron manganese phosphate system have high energy density, excellent cycle performance and fast charging performance.

[0041] In a specific embodiment, the composition of the lithium manganese iron phosphate positive electrode material is LiMn x Fe 1-x PO4, wherein 0.5≤x≤0.9. For example, x can be 0.5, 0.6, 0.7, 0.8, 0.9, or a range consisting of any two of the above values.

[0042] Furthermore, in order to improve the structural stability of the lithium manganese iron phosphate positive electrode material, other elements may be doped therein, including but not limited to one or more of vanadium, magnesium, and titanium.

[0043] In a specific embodiment, the pore-forming agent is prepared by a method comprising the following steps:

[0044] A catalyst and a gas adsorbent are added to a dispersion of lithium supplement particles, and the mixture is heat treated at 50-80° C. for 10-15 hours to obtain a pore-forming agent precursor; and the pore-forming agent precursor is calcined at 600-800° C. for 10-16 hours to obtain a pore-forming agent.

[0045] The catalyst and the gas adsorbent can form a coating layer on the surface of the lithium supplement particles through heat treatment to obtain a precursor, and the precursor can be fully dried through calcination treatment to obtain a pore-forming agent.

[0046] More preferably, the temperature of the heat treatment is 60-70° C., and the time is 12-14 h; the temperature of the calcination treatment is 650-750° C., and the time is 12-14 h.

[0047] In some specific embodiments, the dispersion of lithium-supplementing particles can be obtained by adding the lithium-supplementing particles into a solvent and dispersing the particles, wherein the solvent can be one or more of ethanol, methanol, acetone, and diethyl ether.

[0048] In order to avoid interference from impurities and moisture in the air, the calcination treatment is carried out under an inert gas atmosphere. Specifically, the inert gas may be one or more of nitrogen and argon.

[0049] The present invention does not specifically limit the type of the positive electrode current collector, which may be a positive electrode current collector commonly used in the art, such as aluminum foil.

[0050] The positive electrode active layer of the present invention includes conventional components such as a conductive agent, a binder and a dispersant in addition to the positive electrode active material and the pore former.

[0051] The conductive agent includes, but is not limited to, one or more of conductive carbon black, Super-C, acetylene black, Ketjen black, and carbon nanofiber.

[0052] The binder includes, but is not limited to, one or more of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC-Na), polyvinyl pyrrolidone, polytetrafluoroethylene, and styrene-butadiene rubber (SBR).

[0053] The dispersant includes, but is not limited to, one or more of polyvinyl pyrrolidone, polyethylene glycol, and TC130.

[0054] In a specific embodiment, the positive electrode active layer includes, by mass percentage, 90% to 97% of a positive electrode active material, 1% to 3% of a pore former, 1% to 3.5% of a binder, 0.8% to 3% of a conductive agent, and 0.2% to 0.5% of a dispersant.

[0055] In a specific embodiment, the positive electrode sheet can be prepared by the following method: the positive electrode active material, pore-forming agent, conductive agent and binder are dispersed in a solvent in proportion to obtain a slurry, and the slurry is then coated on one or both sides of the positive electrode collector. The positive electrode sheet can be obtained after drying, slitting and rolling.

[0056] A second aspect of the present invention provides a secondary battery comprising the positive electrode sheet provided in the first aspect. Because the battery includes the aforementioned pore-forming agent having a specific composition and structure, the battery has excellent initial efficiency, energy density, cycle performance, and fast charging performance, as well as low gas production.

[0057] The battery of the present invention includes, in addition to the above-mentioned positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.

[0058] Among them, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. Among them, the negative electrode current collector can be selected from the negative electrode current collectors conventionally used in the art, such as copper foil. The negative electrode active material layer can also refer to the conventional composition in the art, for example, the negative electrode active material layer includes a negative electrode active substance, a conductive agent and a binder. The negative electrode active substance can be selected from the negative electrode active substances conventionally used in the art, including but not limited to one or more of natural graphite, artificial graphite, silicon-carbon material, silicon-oxygen material, and hard carbon. The composition of the conductive agent and the binder can refer to the types of conductive agent and binder in the positive electrode sheet, which will not be repeated here.

[0059] The function of the separator is to separate the positive electrode and the negative electrode, preventing contact and short circuit between the two, and allowing lithium ions to pass freely. The present invention does not specifically limit the type of separator. It can be selected from porous separators commonly used in the art with good chemical and mechanical stability, including but not limited to one or more of polypropylene, polyethylene, glass fiber, and non-woven fabrics.

[0060] The electrolyte is a medium between the positive and negative electrodes that conducts lithium ions. It can be a gel, solid, or liquid electrolyte. This application does not specifically limit the type of electrolyte; it can be selected from gel, solid, or liquid electrolytes commonly used in the art.

[0061] In a specific embodiment, the secondary battery of the present invention can be prepared by the following method: stacking the positive electrode sheet, the separator and the negative electrode sheet in sequence, obtaining a battery cell through a lamination or winding process, and then baking, injecting, forming, packaging and other processes to obtain the secondary battery of the present invention.

[0062] A third aspect of the present invention provides an electrical device comprising the aforementioned secondary battery. The present invention does not particularly limit the type of electrical device; the device may be any electrical device comprising the aforementioned secondary battery, including but not limited to mobile phones, portable devices, laptop computers, electric bicycles, electric vehicles, electric toys, and energy storage devices.

[0063] The following will introduce the positive electrode plate and its preparation method and the secondary battery including the positive electrode plate provided by the present invention in detail through specific embodiments.

[0064] Unless otherwise specified, the reagents, materials, and instruments used in the following examples are conventional reagents, conventional materials, and conventional instruments in the art and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0065] In the following examples and comparative examples, the D50 particle size of the lithium supplement particles was measured using a laser particle size analyzer, and the thickness of the coating layer was measured using FIB-SEM analysis.

[0066] Example 1

[0067] 1. Preparation of positive electrode sheet

[0068] 1) dispersing lithium-supplementing particles Li2O having a particle size D50 of 10 μm in ethanol to obtain a dispersion, then adding ferrous sulfate and Cu powder to the dispersion in a mass ratio of 20:1, such that the mass ratio of the lithium-supplementing particles Li2O, ferrous sulfate, and Cu powder in the dispersion is 2000:20:1; and heat treating the mixture in a reactor at 65° C. for 12 hours to obtain a pore-forming agent precursor having a coating layer thickness of 200 nm;

[0069] The pore-forming agent precursor was calcined in an argon atmosphere at a temperature of 700° C. for 12 h. After the calcination was completed, the precursor was cooled to room temperature and ground to obtain a pore-forming agent.

[0070] 2) LiMn iron manganese phosphate cathode material 0.6 Fe 0.4 PO4, conductive agent carbon nanotubes, binder polyvinylidene fluoride, dispersant polyvinyl pyrrolidone, and pore-forming agent are dispersed in NMP in a mass ratio of 93:2:3:0.5:1.5 to obtain a positive electrode slurry. The positive electrode slurry is prepared at a surface density of 440 g / m 2 , coated on both sides of an aluminum foil with a thickness of 17 μm, baked, rolled and cut to obtain a positive electrode sheet with a thickness of 200 μm.

[0071] 2. Preparation of negative electrode sheet

[0072] The negative electrode active material graphite, conductive agent carbon black, binder styrene butadiene latex SBR, and thickener carboxymethyl cellulose CMC were dispersed in solvent water at a mass ratio of 96:1:1.4:1.6 to obtain a negative electrode slurry. The negative electrode slurry was prepared at a surface density of 194 g / m 2 , coated on both sides of a copper foil with a thickness of 8 μm, baked, rolled and cut to obtain a negative electrode sheet with a thickness of 130 μm.

[0073] 3. Assembly of secondary batteries

[0074] The positive electrode sheet, negative electrode sheet and polypropylene separator prepared above are stacked in the order of positive electrode sheet, separator and negative electrode sheet, and then wound to obtain a battery cell; the battery cell is placed in an aluminum-plastic film, and an electrolyte (the solvent is ethylene carbonate and ethyl methyl carbonate, and the solute is lithium salt lithium hexafluorophosphate LiPF6) is injected. After vacuum packaging, standing, formation, shaping, sorting and other processes, a lithium secondary battery is obtained.

[0075] Examples 2 to 20

[0076] The preparation methods of the positive electrode sheets and secondary batteries of Examples 2 to 20 refer to Example 1, and the specific differences are listed in Table 1.

[0077] Table 1

[0078]

[0079] Comparative Example 1

[0080] This comparative example provides a positive electrode sheet and a lithium secondary battery, the preparation method of which is basically the same as that of Example 1, except that no pore-forming agent is added to the positive electrode active layer, and the positive electrode is LiMn 0.6 Fe 0.4 PO4, conductive agent carbon nanotubes, binder polyvinylidene fluoride, and dispersant polyvinyl pyrrolidone are dispersed in NMP in a mass ratio of 94:2:3:1 to obtain a positive electrode slurry. The other steps are consistent with Example 1 and are not repeated here.

[0081] Comparative Example 2

[0082] This comparative example provides a positive electrode sheet and a lithium secondary battery, the preparation method of which is basically the same as that of Example 1, except that Li2O is directly used as a pore-forming agent without coating ferrous sulfate and Cu powder.

[0083] Comparative Example 3

[0084] This comparative example provides a positive electrode sheet and a lithium secondary battery, the preparation method of which is basically the same as that of Example 1, except that the preparation of the pore-forming agent includes the following steps:

[0085] Lithium-replenishing particles Li2O with a particle size D50 of 10 μm were dispersed in ethanol to obtain a dispersion. Ferrous sulfate and silicon powder were then added to the dispersion in a mass ratio of 20:1, such that the mass ratio of the lithium-replenishing particles Li2O, ferrous sulfate, and silicon powder in the dispersion was 2000:20:1. The mixture was heat treated in a reactor at 65°C for 12 hours to obtain a pore-forming agent precursor with a coating layer thickness of 200 nm.

[0086] The pore-forming agent precursor was washed with alkaline solution and then calcined in an argon atmosphere at a temperature of 700° C. for 12 hours. After the calcination was completed, the pore-forming agent was cooled to room temperature and ground to obtain the pore-forming agent.

[0087] Comparative Example 4

[0088] This comparative example provides a positive electrode sheet and a lithium secondary battery, the preparation method of which is basically the same as that of Example 1, except that the preparation of the pore-forming agent includes the following steps:

[0089] 1) Li2O particles with a particle size D50 of 10 μm were dispersed in ethanol to obtain a dispersion, and Cu powder was added to the dispersion, with a mass ratio of Li2O particles to Cu powder of 2000:21. The dispersion was heat treated in a reactor at 65°C for 12 hours to obtain a pore-forming agent precursor with a coating layer thickness of 200 nm.

[0090] The pore-forming agent precursor was calcined in an argon atmosphere at a temperature of 700° C. for 12 h. After the calcination was completed, the precursor was cooled to room temperature and ground to obtain a pore-forming agent.

[0091] Comparative Example 5

[0092] This comparative example provides a positive electrode sheet and a lithium secondary battery, the preparation method of which is basically the same as that of Example 1, except that the preparation of the pore-forming agent includes the following steps:

[0093] 1) dispersing lithium-ion supplementary particles (Li2O) having a particle size (D50) of 10 μm in ethanol to obtain a dispersion, and then adding ferrous sulfate to the dispersion, wherein the mass ratio of the lithium-ion supplementary particles (Li2O) to the ferrous sulfate in the dispersion is 2000:21; and heat treating the dispersion in a reactor at 65° C. for 12 hours to obtain a pore-forming agent precursor having a coating layer thickness of 200 nm;

[0094] The pore-forming agent precursor was calcined in an argon atmosphere at a temperature of 700° C. for 12 h. After the calcination was completed, the precursor was cooled to room temperature and ground to obtain a pore-forming agent.

[0095] Comparative Example 6

[0096] This comparative example provides a positive electrode sheet and a lithium secondary battery, the preparation method of which is basically the same as that of Example 1, except that amorphous carbon is used instead of Cu powder.

[0097] Test Case

[0098] 1. Porosity

[0099] The porosity of the positive electrode sheets of the above embodiments and comparative examples was tested using a FIB-SEM dual-beam electron microscope. The test results are shown in Table 2.

[0100] 2. Viscosity of positive electrode slurry

[0101] The positive electrode slurries prepared in the above examples and comparative examples were allowed to stand for 12 hours, then subjected to viscosity testing within 10 minutes using a ViscQC 300(L) rotational rheometer. If the viscosity exceeded 3500 mPa·s, the slurry was considered to have formed a gel; if it did not exceed 3500 mPa·s, the slurry was considered to be in good condition. The viscosity test results are shown in Table 2.

[0102] 3. Gas production in the formation stage

[0103] Test method: At 25°C, the Archimedes displacement method is used to measure the volume change of the battery cell before and after formation. The volume change value is the gas production.

[0104] 4. The first effect of volume separation

[0105] Test method: At 25°C, the secondary batteries of the above examples and comparative examples were charged at 1 / 3C constant current and constant voltage to 4.3V, with a cutoff current of 0.05C, and discharged at 1 / 3C constant current to 2.5V. The first effect of the capacity distribution = discharge capacity / charge capacity*100%.

[0106] 5. Fast charging performance

[0107] Test method: At 25°C, the secondary batteries of the above embodiments and comparative examples were charged at a constant current and constant voltage of 0.5C to a cut-off voltage of 4.3V, with a cut-off current of 0.05C, and then discharged at a constant current of 0.5C to a lower limit voltage of 2.5V, and the discharge capacity was recorded as Q0. Then, they were charged at 3C to an upper limit voltage of 4.3V, and the battery capacity Q1 after charging for 20 minutes was recorded. The fast charging capability of the battery was evaluated by the value of Q1 / Q0×100%. The larger the value, the better the fast charging performance.

[0108] 6. Cycle performance

[0109] Test method: At 45°C, the secondary batteries of the above embodiments and comparative examples were charged at 0.5C constant current and constant voltage to 4.3V, with a cutoff current of 0.05C, and discharged at 0.5C constant current to 2.5V for 500 cycles. The capacity retention rate after 500 cycles = discharge capacity at the 500th cycle / discharge capacity at the first cycle * 100%.

[0110] The test results of the above performance are shown in Table 2.

[0111] Table 2

[0112]

[0113]

[0114] The following conclusions can be drawn from Table 2:

[0115] 1) Comparing the test results of Examples 1 to 20 and Comparative Example 1, it can be confirmed that the pore-forming agent with lithium-supplementing particles as the core and catalyst and gas adsorbent as the coating layer can not only make up for the irreversible capacity loss during the first charge and discharge and improve the first efficiency, but its multi-porous coating layer can also meet the optimization of ion transport and significantly improve the fast charging performance of the battery.

[0116] 2) According to the comparison between Example 1 and Comparative Example 2, when there is no gas adsorbent in the coating layer, the oxidizing gas generated by the decomposition of the lithium-replenishing particles will deteriorate the electrode interface, resulting in the failure to achieve the lithium-replenishing effect, and the gas production will increase significantly, further affecting the fast charging performance of the battery.

[0117] 3) By comparing the results of Example 1 and Comparative Example 3, it can be seen that the pore-forming agent coating effect of Example 1 is better, ensuring the air stability of the lithium replenisher, preventing the reaction with H2O and CO2 to generate residual alkali, cross-linking with the binder in the slurry, resulting in gelation and affecting the electrode yield, and avoiding particle agglomeration leading to uneven current density distribution, so the rate performance is better, and the catalyst can enable the lithium replenisher to completely decompose and release lithium at a conventional formation voltage, so the lithium replenishment effect is better.

[0118] 4) By comparing the results of Example 1 and Comparative Example 4, it can be seen that Comparative Example 4 only coated the catalyst. Although it accelerated the decomposition and pore formation of the lithium replenishing agent, it produced severe gas that damaged the electrode interface, causing the SEI film to be continuously damaged and repaired, consuming the electrolyte and active lithium, resulting in a lithium replenishment effect worse than that of Example 1. In addition, the electrolyte had residual active oxygen, which subsequently oxidized the electrolyte to produce gas, greatly affecting the capacity.

[0119] 5) By comparing the results of Example 1 and Comparative Example 5, it can be seen that Comparative Example 5 only coats the gas adsorbent on the surface of the lithium-supplementing particles. Although this reduces the risk of gas production, similar to Comparative Examples 2-3, due to the lack of a catalyst, the lithium-supplementing agent is not completely decomposed at the formation voltage, resulting in insufficient pore formation and lithium replenishment, resulting in a lower porosity of the positive electrode sheet, poor fast charging performance, cycle performance, and initial efficiency.

[0120] 6) By comparing the results of Example 1 and Comparative Example 6, it can be seen that when the copper powder coating the surface of the lithium-supplementing particles is replaced with carbon material, compared with metallic copper, which has a large number of free electrons that can conduct electricity, carbon has stable chemical bonds, a small number of free electrons, and a poor catalytic effect, resulting in insufficient lithium release and thus poor performance.

[0121] 7) Compared with Example 1, Example 2, and Examples 14 and 15, the particle size of the lithium supplement particles in Examples 14 and 15 is larger, which is beneficial to the increase in pore size and lithium ion transmission. However, the particle size of the lithium supplement agent in Example 15 is too large. Although the porosity of the electrode is further increased, the increase rate is reduced. This is because it is difficult for the catalyst to approach the center of the lithium supplement particle within the same formation time, resulting in insufficient lithium release and affecting the pore formation effect.

[0122] 8) Compared with Examples 1, 3, 16, and 17, reducing the gas adsorbent ratio improved the catalytic decomposition effect, but also increased gas production. In particular, in Example 16, the gas adsorbent ratio was too low, and gas production separated the electrode, hindering ion transport, affecting capacity utilization, and affecting rate and cycle performance. In Example 3, the gas adsorbent ratio was relatively high, resulting in a low catalyst dosage, which led to incomplete decomposition of some lithium-supplementing particles, reduced initial efficiency, and undecomposed lithium-supplementing particles occupying channels, resulting in a lower rate charge capacity ratio than in Example 1.

[0123] 9) Compared with Example 1, Example 4 has a thicker coating layer. Although the gas production is further controlled, the contact path between the free catalyst and the lithium-supplementing particles is extended. Under the same formation time, the lithium release is insufficient. Similarly, the subsequent lithium ion mass transfer rate is also affected, resulting in a decrease in fast charging performance.

[0124] 10) Comparing Example 5 with Example 1, it can be seen that the calcination conditions of Example 1 allow the pore-forming agent to be formed earlier and more completely without particle agglomeration, so the slurry is in good condition and the battery rate performance is better.

[0125] 11) Comparison of Examples 1, 6, and 7 reveals that, under the same conditions, using Cu, Fe, and Ni as catalysts, respectively, results in no significant difference in lithium replenishment and rate performance. However, both Fe and Ni are ferromagnetic, leading to current hotspots and impacting cycling performance. Furthermore, the electrical conductivity of CuO in Example 8 is only 10% to 50% of that of metallic Cu, significantly impacting the decomposition of the lithium replenisher, resulting in decreased positive electrode porosity, and reduced initial efficiency, fast charge, and cycling performance.

[0126] 12) Comparison of Examples 3, 9, and 10 shows that when ferrous sulfate, sodium sulfite, and aluminum oxide are used as gas adsorbents, all battery performance is superior. Compared to ferrous sulfate and sulfite, aluminum oxide can also adsorb other gases besides oxygen, alleviating gas production during film formation and optimizing the electrode interface. Consequently, it produces lower gas production and slightly better cycle performance.

[0127] 13) By comparing Examples 10 to 13, it can be seen that under the same conditions, the decomposition and delithiation capacity of the lithium-supplementing particles Li2NiO2, Li5FeO4, and Li2CO3 used in Examples 11 to 13 are lower than that of Li2O in Example 10, resulting in a reduction in the irreversible capacity loss that can be supplemented, while affecting the subsequent cycle capacity retention rate.

[0128] 14) Comparison of Examples 1, 18, 19, and 20 shows that as the proportion of pore-forming agent added increases, the porosity of the positive electrode plate gradually increases, significantly improving rate performance. While Example 19, with the highest proportion of pore-forming agent added, exhibits the highest rate performance and plate porosity, at the same plate surface density, the positive electrode has limited vacancies, leaving more active lithium at the negative electrode as pre-stored lithium. This results in a low negative electrode potential and the risk of lithium plating during cycling, impacting cycle capacity retention.

[0129] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode plate, characterized in that: It includes a positive electrode current collector and a positive electrode active layer arranged on one side or both sides of the positive electrode current collector; the positive electrode active layer includes a positive electrode active material and a pore-forming agent; The pore-forming agent includes lithium-supplementing particles and a coating layer coated on the surface of the lithium-supplementing particles. The coating layer includes a catalyst and a gas adsorbent. The catalyst is selected from one or more of Fe, Cu, Ni and metal oxides thereof.

2. The positive electrode sheet according to claim 1, characterized in that: The gas adsorbent includes one or more of sulfite, ferrous salt, and aluminum oxide.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: The lithium supplement particles include one or more of Li2O, Li2O2, Li2NiO2, Li5FeO4 and Li2CO3.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The D50 particle size of the lithium supplement particles is 5 to 20 μm, preferably 10 to 15 μm; And / or, the coating layer has a thickness of 100 to 300 nm, preferably 150 to 250 nm.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The mass ratio of the gas adsorbent to the catalyst is (10-30):1, preferably (15-25):

1.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: Based on the total mass of the positive electrode active layer, the mass content of the pore former is 1% to 3%, preferably 1.5% to 2.5%.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: The positive electrode active material includes lithium manganese iron phosphate.

8. The positive electrode sheet according to any one of claims 1 to 7, characterized in that: The pore-forming agent is prepared by a method comprising the following steps: A catalyst and a gas adsorbent are added to a dispersion of lithium supplement particles, and the mixture is heat treated at 50-80° C. for 10-15 hours to obtain a pore-forming agent precursor; and the pore-forming agent precursor is calcined at 600-800° C. for 10-16 hours to obtain the pore-forming agent.

9. A secondary battery, characterized in that: The positive electrode sheet comprises the positive electrode sheet according to any one of claims 1 to 8.

10. An electrical device, characterized in that: The secondary battery according to claim 9 is included.

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