Positive pole piece, lithium ion battery and electric device

Abstract

The invention discloses a positive pole piece, a lithium ion battery and an electric device, the positive pole piece comprises a positive active material and an additive, the positive active material comprises transition metal elements, the additive comprises silicon nitride, and the mass ratio of the silicon nitride in the additive is more than 50%. According to the invention, the additive taking silicon nitride as a main component is added into the positive electrode, and the silicon nitride can react with trace water and HF in the battery to generate a silicic acid precipitate which is weaker than carbonic acid in acidity, so that the trace water in the battery is removed, the acid environment in the battery is weakened, and the dissolution of transition metal elements in the positive electrode active material is reduced; further, deposition of transition metal elements at the negative electrode is reduced, cliff type capacity reduction in the life cycle of the battery is avoided, and the cycle performance and the service life of the battery, especially the high-temperature service life, are effectively improved.

Description

Technical Field

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

[0002] At present, with the popularization of new energy electric vehicles, people have higher requirements for electric vehicles, pursuing longer mileage and faster charging speed. Developing lithium-ion batteries with ultra-long life and super-fast charging has become a key goal.

[0003] For lithium-ion batteries, the reasons for life attenuation mainly include the loss caused by the continuous dissolution, rupture, repair, and reorganization of the negative electrode SEI film, which consumes active lithium, and the capacity and material structure loss caused by the large amount of dissolution of transition metal elements in the positive electrode active material caused by trace water and acid in the battery and the deposition on the negative electrode. Since a large amount of metal deposition will cause a cliff-like decrease in battery capacity, it is necessary to avoid metal deposition on the negative electrode as much as possible. However, the commonly used electrolyte lithium salt LiPF6 in the industry at present is unstable, easily pyrolyzed itself, and undergoes a hydrolysis reaction in the presence of trace water to generate HF. HF is likely to cause the dissolution of transition metal elements in the positive electrode active material, and then deposit on the negative electrode. After a large amount accumulates, it will lead to a cliff-like attenuation of life. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems in the related art to some extent. For this reason, an object of the present invention is to provide a positive electrode sheet, which can effectively reduce the deposition of transition metal elements on the negative electrode, and thus effectively improve the cycle performance and service life of the battery.

[0005] Specifically, in a first aspect of the present invention, a positive electrode sheet is provided, which includes a positive electrode active material and an additive. The positive electrode active material contains transition metal elements, and the component of the additive includes silicon nitride, and the mass ratio of silicon nitride in the additive is more than 50%.

[0006] The present invention adds an additive mainly composed of silicon nitride to the positive electrode. Silicon nitride can react with trace water and HF in the battery to generate silicic acid precipitate with a weaker acidity than carbonic acid, thereby removing the trace water in the battery, weakening the acid environment in the battery, reducing the dissolution of transition metal elements in the positive electrode active material, and further reducing the deposition of transition metal elements on the negative electrode, avoiding a cliff-like decrease in battery capacity during the battery life cycle, and effectively improving the cycle performance and service life of the battery, especially the high-temperature service life.

[0007] According to some embodiments of the present invention, the mass ratio of silicon nitride in the additive is more than 90%, and can be selected from 90% - 99%.

[0008] According to some embodiments of the present invention, based on the positive electrode active material, the content of the additive is 0.05 wt% - 0.3 wt%.

[0009] According to some embodiments of the present invention, the content of the additive is 0.05 wt% - 0.1 wt%.

[0010] According to some embodiments of the present invention, the additive is a particulate mesoporous material.

[0011] According to some embodiments of the present invention, the additive is an electro-inert material.

[0012] According to some embodiments of the present invention, the composition of the additive further includes at least one of titanium nitride and SiO₂.

[0013] According to some embodiments of the present invention, the transition metal element includes one or more of iron, manganese, nickel, and cobalt.

[0014] According to some embodiments of the present invention, the positive electrode active material includes one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium nickel manganate, lithium cobaltate, lithium nickel cobalt manganate, lithium nickelate, and lithium-rich manganese-based positive electrode materials.

[0015] The second aspect of the present invention provides a lithium-ion battery, including the positive electrode sheet of the first aspect of the present invention. Due to the adoption of the above positive electrode sheet, the lithium-ion battery of the present invention has all the advantages of the positive electrode sheet, which will not be elaborated herein.

[0016] The third aspect of the present invention provides an electrical device, including the lithium-ion battery of the second aspect of the present invention. Due to the adoption of the above positive electrode sheet, the electrical device of the present invention has all the advantages of the positive electrode sheet, which will not be elaborated herein.

[0017] The additional aspects and advantages of the present invention will be partly given in the following description, partly will become obvious from the following description, or will be understood through the practice of the present invention. Description of the Drawings

[0018] Figure 1 It is a scanning electron microscope image of the additive prepared in Preparation Example 1 of the present invention. Detailed Embodiments

[0019] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0020] In the description of the present invention, unless otherwise specified, "a plurality of" means two or more. "A variety of" means two or more. In this text, the term "comprising" or "including" is an open expression, that is, it includes the content specified in the present invention, but does not exclude other aspects.

[0021] In the ranges disclosed herein, the endpoints and any values of the ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0022] At the present stage, with the popularization of new energy electric vehicles, people have higher requirements for electric vehicles, pursuing longer mileage and faster charging speed. Developing lithium-ion batteries with ultra-long life and super-fast charging has become a key goal.

[0023] For lithium-ion batteries, the main reasons for life attenuation mainly include the loss caused by the continuous dissolution, rupture, repair, and reorganization of the negative electrode SEI film, which consumes active lithium, and the capacity and material structure loss caused by the large amount of dissolution of transition metal elements in the positive electrode active material caused by trace water and acid in the battery and the deposition on the negative electrode. Since a large amount of metal deposition will cause a cliff-like decrease in battery capacity, it is necessary to avoid metal deposition on the negative electrode as much as possible. However, the commonly used electrolyte lithium salt LiPF6 in the current industry is unstable, easily thermally decomposed itself, and undergoes a hydrolysis reaction in the presence of trace water to generate HF. HF is likely to cause the dissolution of transition metal elements in the positive electrode active material, and then deposit on the negative electrode. After a large amount accumulates, it leads to a cliff-like attenuation of life.

[0024] To solve the above problems, the present invention adds an additive mainly composed of silicon nitride to the positive electrode. Silicon nitride can react with trace water and HF in the battery to generate silicic acid precipitate with a weaker acidity than carbonic acid, thereby removing the trace water in the battery, weakening the acid environment in the battery, reducing the dissolution of transition metal elements in the positive electrode active material, and further reducing the deposition of transition metal elements on the negative electrode, avoiding a cliff-like decrease in battery capacity during the battery life cycle, and effectively improving the cycle performance and service life of the battery, especially the high-temperature service life.

[0025] Specifically, in the first aspect of the present invention, a positive electrode tab is provided, which includes a positive electrode active material and an additive. The positive electrode active material contains transition metal elements, and the component of the additive includes silicon nitride, and the mass ratio of silicon nitride in the additive is more than 50%.

[0026] The reaction equation of silicon nitride with trace water and HF in the battery is as follows:

[0027] Si3N4 + 4HF + 9H2O === 3H2SiO3↓ + 4NH4F

[0028] Related technical research has found that the electrolyte additive vinylene carbonate (VC) can reduce the deposition of transition metals on the negative electrode. However, during the battery aging process, due to the destruction and reorganization of the negative electrode SEI film, the electrolyte is continuously involved in the reaction, and VC with a high film-forming potential will react preferentially. To meet the pursuit of long life, a large amount of VC needs to be added. However, the film impedance formed by VC is too large, resulting in too large battery impedance, which is contrary to the pursued fast charging performance. And because the additive of the present invention has the functions of removing water and suppressing acid and reducing the deposition of transition metal elements on the negative electrode, the amount of VC in the electrolyte can be reduced, thereby reducing the impedance of the battery negative electrode. Therefore, the present invention can not only improve the cycle performance and service life of the battery, but also improve the kinetic performance and power performance of the battery by using as little VC as possible.

[0029] In addition, reducing the dissolution of the positive electrode metal is beneficial to improving the chemical stability of the positive electrode active material, truncating the damage of metal deposition to the negative electrode, blocking the possibility of battery diving, and thus is beneficial to improving the storage performance and high-temperature performance of the battery.

[0030] In some embodiments, the mass ratio of silicon nitride in the additive may be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99% or 100%. At the same addition amount, when the mass ratio of silicon nitride is too small, the effects of inhibiting metal dissolution, improving cycle performance and service life become weak. The mass ratio of silicon nitride is preferably within the scope of the present invention.

[0031] In some embodiments, the mass ratio of silicon nitride in the additive may be more than 90%, and may be selected from 90% - 99%, for example, may be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%. The increase in the mass ratio of silicon nitride can reduce the usage amount of the additive and improve the energy density of the battery.

[0032] In some embodiments, based on the positive electrode active material, the content of the additive may be 0.05 wt% - 0.3 wt%. In other words, the mass ratio of the additive to the positive electrode active material is (0.05 - 0.3):100. Due to the strong stoichiometric relationship between silicon nitride and water and acid, the amount of the additive required is only at the ppm level, and the trace amount of the additive has little impact on the battery capacity and cost. If the usage amount of the additive is less than 0.05 wt%, the water and HF in the battery cannot be completely removed; if the usage amount of the additive is greater than 0.3%, which exceeds the amount required for reacting with the water and acid in the battery, the energy density of the battery will be reduced and the cost will be increased.

[0033] In some specific embodiments, the content of the additive may be 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt% or 0.3 wt%.

[0034] In some embodiments, the content of the additive may be 0.05 wt% - 0.1 wt%, such as 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt% or 0.1 wt%.

[0035] In some embodiments, the additive is a granular mesoporous material. The mesoporous material has a mesoporous structure inside, making its liquid retention performance good. At the same time, lithium ions can easily pass through, reducing the impedance of the battery positive electrode and improving the kinetic performance and power performance of the battery.

[0036] In some embodiments, the pore diameter of the mesoporous material may be 5 nm - 10 nm. Optimizing the pore diameter of the mesoporous material is beneficial to balancing the structural stability of the additive and the continuity of the conductive network, thereby being beneficial to improving the cycle performance and service life of the battery. A smaller pore diameter increases the specific surface area and provides more reaction sites, but may agglomerate and is not easy to disperse; a larger pore diameter may promote the transmission of lithium ions, but affects the conductivity of the additive. If the pore diameter is too large, TiN may not form a continuous conductive network, resulting in hindered electron transmission. In some specific embodiments, the pore diameter of the mesoporous material may be 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm. The additive may include mesopores with different pore sizes.

[0037] In some embodiments, the particle size of the additive may be 1 μm - 2 μm. In some specific embodiments, the particle size of the additive may be 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm. The additive may include particles with different particle sizes.

[0038] The additive of the present invention has strong rigidity and is difficult to press during rolling. It plays a role in supporting the lithium ion channels, which is beneficial to forming a transmission path with low tortuosity in the positive electrode sheet, making lithium ions easier to pass through, reducing the impedance of the battery positive electrode, and improving the kinetic performance and power performance of the battery.

[0039] In some embodiments, the additive is an electro-inert material. The electro-inert material does not participate in oxidation and reduction reactions during charge and discharge, does not participate in the film formation of the positive and negative electrodes, and has no influence on the amount of lithium ions in the entire battery system and the electrochemical reaction of the electrolyte. Since the additive is an electro-inert material, the dosage of the additive cannot be too much, otherwise it will lead to poor conductivity, increase the internal resistance of the battery, and reduce the kinetic performance of the battery.

[0040] In some embodiments, the composition of the additive further includes at least one of titanium nitride and SiO2. Titanium nitride (TiN) can enhance conductivity.

[0041] In some embodiments, the transition metal element includes one or more of iron, manganese, nickel, and cobalt. In the presence of water and HF, these transition metal elements in the positive electrode active material may all dissolve out. By adding the additive to the positive electrode in the present invention, the dissolution amount of these transition metal elements can be reduced, and the cycle performance and lifespan of the battery can be improved.

[0042] In some embodiments, the positive electrode active material includes one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium nickel manganate, lithium cobaltate, lithium nickel cobalt manganate, lithium nickelate, and lithium-rich manganese-based positive electrode materials. These positive electrode active materials are commonly used positive electrode materials. Of course, the positive electrode active material of the present invention is not limited to these.

[0043] The second aspect of the present invention provides a lithium-ion battery, including the positive electrode sheet of the first aspect of the present invention. Due to the adoption of the above positive electrode sheet, the lithium-ion battery of the present invention has all the advantages of the positive electrode sheet, which will not be elaborated here.

[0044] The third aspect of the present invention provides an electrical device, including the lithium-ion battery of the second aspect of the present invention. Due to the adoption of the above positive electrode sheet, the electrical device of the present invention has all the advantages of the positive electrode sheet, which will not be elaborated here.

[0045] The solution of the present invention will be explained below in conjunction with embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0046] Preparation of the additive

[0047] Preparation Example 1: Mesoporous Additive 1

[0048] 17.5 g of tetraethyl orthosilicate (TEOS) and 3.5 g of tetrabutyl titanate (TBOT) were dissolved in 80 g of absolute ethanol, and 0.1 mol of nitric acid was added to adjust the pH to 4. Stir to form a homogeneous sol. The activated SBA-15 (purchased from Merck) was immersed in the above precursor, evacuated 5 times to ensure that the precursor completely filled the pores, left standing for 12 h to gel, calcined at 500 °C in air to be converted into SiO2-TiO2 composite oxide. The sample was placed in a tube furnace, high-purity N2 was introduced, and the temperature was programmed (0 °C - 800 °C - 1200 °C), and then naturally cooled to room temperature to obtain the mesoporous additive Si3N-TiN. The mass ratio of silicon nitride in mesoporous additive 1 was 95%. The scanning electron microscope image of mesoporous additive 1 is as shown in Figure 1 shown.

[0049] Preparation Example 2: Mesoporous additive 2

[0050] 8.3 g of tetraethyl orthosilicate (TEOS) and 3.5 g of tetrabutyl titanate (TBOT) were dissolved in 80 g of absolute ethanol, and 0.1 mol of nitric acid was added to adjust the pH to 4. Stir to form a homogeneous sol. The activated SBA-15 was immersed in the above precursor, evacuated 5 times to ensure that the precursor completely filled the pores, left standing for 12 h to gel, calcined at 500 °C in air to be converted into SiO2-TiO2 composite oxide. The sample was placed in a tube furnace, high-purity N2 was introduced, and the temperature was programmed (0 °C - 800 °C - 1200 °C), and then naturally cooled to room temperature to obtain the mesoporous additive Si3N-TiN. The mass ratio of silicon nitride in mesoporous additive 2 was 90%.

[0051] Preparation Example 3: Mesoporous additive 3

[0052] 0.92 g of tetraethyl orthosilicate (TEOS) and 3.5 g of tetrabutyl titanate (TBOT) were dissolved in 80 g of absolute ethanol, and 0.1 mol of nitric acid was added to adjust the pH to 4. Stir to form a homogeneous sol. The activated SBA-15 was immersed in the above precursor, evacuated 5 times to ensure that the precursor completely filled the pores, left standing for 12 h to gel, calcined at 500 °C in air to be converted into SiO2-TiO2 composite oxide. The sample was placed in a tube furnace, high-purity N2 was introduced, and the temperature was programmed (0 °C - 800 °C - 1200 °C), and then naturally cooled to room temperature to obtain the mesoporous additive Si3N-TiN. The mass ratio of silicon nitride in mesoporous additive 3 was 50%.

[0053] Preparation Comparative Example 1: Mesoporous additive 4

[0054] Dissolve 0.65 g of tetraethyl orthosilicate (TEOS) and 3.5 g of tetrabutyl titanate (TBOT) in 80 g of absolute ethanol, add 0.1 mol of nitric acid to adjust the pH to 4, and stir to form a homogeneous sol. Immerse the activated SBA-15 into the above precursor, evacuate 5 times to ensure that the precursor completely fills the pores, let it stand for 12 h to gel, and calcine at 500 °C in air to convert it into SiO2-TiO2 composite oxide. Place the sample in a tube furnace, introduce high-purity N2, and perform programmed heating (0 °C - 800 °C - 1200 °C), and then naturally cool to room temperature to obtain mesoporous additive Si3N-TiN. The mass ratio of silicon nitride in mesoporous additive 4 is 40%.

[0055] Prepare a lithium-ion battery

[0056] Application Example 1

[0057] (1) Preparation of the positive electrode sheet

[0058] Mix the positive electrode active material lithium iron phosphate LFP, the conductive agent acetylene black and carbon nanotubes CNT (mass ratio 2:3), and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 97.5:0.5:2, add 0.05 wt% of mesoporous additive 1 (based on LFP), add the solvent N-methylpyrrolidone (NMP), stir to form a uniform slurry, uniformly coat the positive electrode slurry on the positive electrode current collector aluminum foil, and after drying, roll, cut, and die-cut it into a positive electrode sheet.

[0059] (2) Preparation of the negative electrode sheet

[0060] Mix the negative electrode active material graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) in a mass ratio of 95.5:1:1.5:2, add deionized water and stir to form a uniform slurry; uniformly coat the negative electrode slurry on the negative electrode current collector copper foil, and after drying in an oven, roll, cut, and die-cut it into a negative electrode sheet.

[0061] (3) Preparation of the electrolyte

[0062] Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 and add 2% (based on the total mass of the electrolyte) of vinylene carbonate (VC) to obtain a mixed organic solvent. Then dissolve the fully dried lithium salt LiPF6 in the mixed organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L.

[0063] (4) Preparation of the separator

[0064] Use 15 μm thick polypropylene as the separator.

[0065] (5) Preparation of the lithium-ion battery

[0066] Stack the above-mentioned positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive and negative electrode sheets to isolate the positive and negative electrodes. Then, obtain the electrode core through stacking. Place the electrode core in the outer packaging case, inject the electrolyte, and after processes such as encapsulation, standing, formation, and grading, obtain the lithium-ion battery.

[0067] Application Example 2

[0068] Prepare the lithium-ion battery according to the method of Application Example 1, except that 0.1 wt% of mesoporous additive 1 (based on LFP) is added.

[0069] Application Example 3

[0070] Prepare the lithium-ion battery according to the method of Application Example 1, except that 0.3 wt% of mesoporous additive 1 (based on LFP) is added.

[0071] Application Example 4

[0072] Prepare the lithium-ion battery according to the method of Application Example 1, except that 0.4 wt% of mesoporous additive 1 (based on LFP) is added.

[0073] Application Example 5

[0074] Prepare the lithium-ion battery according to the method of Application Example 1, except that 0.03 wt% of mesoporous additive 1 (based on LFP) is added.

[0075] Application Example 6

[0076] Prepare the lithium-ion battery according to the method of Application Example 1, except that mesoporous additive 2 is used to replace mesoporous additive 1.

[0077] Application Example 7

[0078] Prepare the lithium-ion battery according to the method of Application Example 1, except that mesoporous additive 3 is used to replace mesoporous additive 1.

[0079] Application Example 8

[0080] Prepare the lithium-ion battery according to the method of Application Example 1, except that NCM811 is used as the positive active material to replace LFP.

[0081] Application Comparative Example 1

[0082] Prepare the lithium-ion battery according to the method of Application Example 1, except that mesoporous additive 1 is not used.

[0083] Application Comparative Example 2

[0084] The lithium-ion battery was prepared according to the method of Application Example 1, except that mesoporous additive 1 was not used and the addition amount of VC was increased to 3%.

[0085] Application Comparative Example 3

[0086] The lithium-ion battery was prepared according to the method of Application Example 1, except that mesoporous additive 4 was used to replace mesoporous additive 1.

[0087] Performance Test of Lithium-Ion Battery

[0088] (1) High-Temperature Cycling Performance Test

[0089] Two batteries prepared from the same example or the same comparative example were respectively placed in an environmental chamber at 60 °C. After standing for 4 h, they were charged at a constant current of 1C to 3.8V, then stood for 10 min, and discharged at a constant current of 1C to 2.0V. The obtained capacity was recorded as the initial capacity C0. After standing for 10 min, the two batteries were cycled 500 times and 1000 times respectively according to the above steps, and the discharge capacity C of the battery after cycling the corresponding number of times was recorded. n , the capacity retention rate P of the battery n = C n / C0 * 100%. The test results are shown in Table 1.

[0090] (2) Fast Charging Performance Test

[0091] After the battery was left standing for 10 min, it was charged at a constant current of 1 / 3C to 3.8V, then left standing for 10 min, and discharged at a constant current of 1 / 3C to 2.0V. After standing for 10 min, this was repeated 3 times, and the discharge capacity of the third time was recorded as C0.

[0092] The battery was successively charged at constant currents of 0.33C0, 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3.0C0, 3.5C0, 4.0C0, 4.5C0, 5.0C0, 5.5C0, 6C0 to the full battery charging cut-off voltage of 3.8V or the 0V negative electrode cut-off potential (whichever is reached first). After each charge was completed, it was discharged at 0.33C0 to 2V, and the negative electrode potential corresponding to when charging reached 10% SOC, 20% SOC, 30% SOC,..., 80% SOC (State of Charge) at different charging rates was recorded. A charging rate-negative electrode potential curve at different SOC states was plotted, and after linear fitting, the charging rate corresponding to when the negative electrode potential was 0V at different SOC states was obtained. This charging rate was the charging window at that SOC state, and was respectively denoted as C 10％SOC , C 20％SOC , C 30％SOC , C 40％SOC , C 50％SOC , C 60％SOC, C 70％SOC , C 80％SOC , the charging time t for the battery to be charged from 0% SOC to 80% SOC is calculated according to the following formula: (60 / C 10％SOC + 60 / C 20％SOC + 60 / C 30％SOC + 60 / C 40％SOC + 60 / C 50％SOC + 60 / C 60％SOC + 60 / C 70％SOC + 60 / C 80％SOC ) × 10%. The test results are shown in Table 1.

[0093] (3) Negative electrode iron content test

[0094] Disassemble the battery after the high-temperature cycle test above (i.e., the batteries with 500 cycles and 1000 cycles) in the glove box, clean the negative electrode plate with dimethyl carbonate DMC. After baking the negative electrode plate, scrape off the negative electrode material with a ceramic knife, grind it, and test the iron content in the electrode plate powder with an inductively coupled plasma optical emission spectrometer (ICP). The test results are shown in Table 1.

[0095] Table 1

[0096]

[0097]

[0098] Results and discussion

[0099] By comparing Application Examples 1-7 and Application Comparative Example 1, it can be seen that in Application Comparative Example 1, no additive was used, the Fe deposited on the negative electrode increased significantly, the cycle performance deteriorated significantly, and from the perspective of the capacity retention rate after 1000 cycles, the service life of Application Comparative Example 1 was significantly shorter and the fast charging performance decreased.

[0100] By comparing Application Example 1 and Application Comparative Example 2, it can be seen that in Application Comparative Example 2, no additive was used. After significantly increasing the VC addition amount in the electrolyte, the Fe content deposited on the negative electrode, the cycle performance, and the service life were only comparable to those of Application Example 1. However, due to the relatively large impedance of the negative electrode film formed by VC participation, the fast charging ability was significantly reduced and the fast charging time was significantly prolonged.

[0101] By comparing Application Example 1, Application Examples 6-7 and Application Comparative Example 3, it can be seen that in Application Comparative Example 3, the mass ratio of silicon nitride in the additive became smaller, which led to an increase in the Fe content deposited on the negative electrode and a weakening of the improvement effect on the cycle performance, service life, and fast charging performance.

[0102] By comparing Application Examples 1-5, it can be seen that when the dosage of the additive is in the range of 0.05 wt% - 0.1 wt%, the improvement of battery performance is the most obvious. As the dosage of the additive increases, the Fe content deposited on the negative electrode gradually decreases, the cycle performance and service life are gradually improved, and the fast charging performance gradually deteriorates, which is caused by the electro-inertness of the additive.

[0103] By comparing Application Example 1 and Application Example 8, it can be seen that the additive of the present invention is applicable to different cathode active material systems and can reduce the Fe content deposited on the negative electrode.

[0104] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0105] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A positive electrode sheet, characterized in that, It includes a positive electrode active material and an additive. The positive electrode active material contains a transition metal element. The composition of the additive includes silicon nitride, and the mass ratio of silicon nitride in the additive is more than 50%.

2. The positive electrode sheet according to claim 1, characterized in that, The mass ratio of silicon nitride in the additive is more than 90%, and can be optionally 90%-99%.

3. The positive electrode sheet according to claim 1, characterized in that, Based on the positive electrode active material, the content of the additive is 0.05wt%-0.3wt%.

4. The positive electrode sheet according to claim 3, wherein, The content of the additive is 0.05wt%-0.1wt%.

5. The positive electrode sheet according to claim 1, wherein, The additive is a granular mesoporous material.

6. The positive electrode sheet according to claim 1, characterized in that, The additive is an electro-inert material.

7. The positive electrode sheet according to claim 1, characterized in that The composition of the additive further includes at least one of titanium nitride and SiO2.

8. The positive electrode sheet according to claim 1, characterized in that, The transition metal element includes one or more of iron, manganese, nickel, and cobalt.

9. The positive electrode sheet according to claim 1, wherein, The positive electrode active material includes one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium nickel manganate, lithium cobaltate, lithium nickel cobalt manganate, lithium nickelate, and lithium-rich manganese-based positive electrode materials.

10. A lithium-ion battery, characterized in that, It includes the positive electrode sheet according to any one of claims 1-9.

11. An electrical device, characterized in that, It includes the lithium-ion battery according to claim 10.

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