Secondary battery, method of manufacturing, and electric device using the same

Abstract

The present application relates to a kind of secondary batteries, preparation method and its electric device. Wherein, including the negative pole sheet of negative pole active material and the positive pole sheet of including positive pole active material;The porosity of negative pole active material is 40%~60%, the porosity of positive pole active material is 50%~70%, and the ratio of negative pole sheet and positive pole sheet porosity is in the range of 1.2~1.8.The pulse release performance of the above-mentioned secondary battery is better, and better power performance and higher capacity retention rate can be obtained.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to a secondary battery, its preparation method, and its electrical equipment. Background Technology

[0002] With the development of lithium battery technology and its industrial applications, people have placed more and higher demands on battery performance. For example, they require rapid charging in the shortest possible time, high power output, and ultra-long cycle life. However, existing rechargeable batteries suffer from problems such as high DC internal resistance, poor power performance, and short lifespan, making it impossible to simultaneously meet the performance requirements of fast charging, high pulse power, and long cycle life. Summary of the Invention

[0003] This invention provides a secondary battery, a preparation method, and an electrical device thereof, to solve the technical problem in the prior art that secondary batteries are difficult to simultaneously achieve fast charging, high pulse power, and long cycle life.

[0004] The secondary battery provided by the present invention includes a negative electrode sheet containing a negative electrode active material and a positive electrode sheet containing a positive electrode active material;

[0005] The porosity of the negative electrode active material is 40% to 60%;

[0006] The porosity of the positive electrode active material is 50% to 70%;

[0007] The porosity ratio of the negative electrode to the positive electrode is 1.2 to 1.8.

[0008] Furthermore, the porosity of the negative electrode is 32% to 39%; the porosity of the positive electrode is 20% to 27%.

[0009] Furthermore, the positive electrode active material includes materials with the chemical formula Li. x Ni y Co z Mn k M p A compound of O2, wherein M contains at least one of Y, Nb, In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, Cr or Fe, and 0.8≤x≤1.2, 0<y<1, 0<z<1, 0<k<1, 0≤p≤0.1.

[0010] Furthermore, in the pores of the positive electrode active material, the sum of the volumes of pores in the 100–300 nm range is 0.0025–0.03 mL / g, and the sum of the volumes of pores in the 500–2000 nm range is 0.2–0.4 mL / g; the ratio of the sum of the volumes of pores in the 100–300 nm range to the sum of the volumes of pores in the 500–2000 nm range is 1%–10%.

[0011] Furthermore, the compaction density of the negative electrode sheet is 1.0 to 1.5 g / cc.

[0012] Furthermore, the compaction density of the positive electrode sheet is 2.5–3.3 g / cc.

[0013] Furthermore, the surface of the negative electrode active material has a coating layer, which includes a carbon material.

[0014] Another aspect of the present invention provides a method for preparing a secondary battery, the method comprising:

[0015] Preparation of negative electrode and preparation of positive electrode;

[0016] The preparation of the negative electrode sheet includes covering the surface of the negative electrode current collector with a negative electrode slurry containing a negative electrode active material with a porosity of 40% to 60%, performing a first roll pressing and a second roll pressing, and then drying.

[0017] The preparation of the positive electrode sheet includes coating the surface of the positive electrode current collector with a positive electrode slurry containing a positive electrode active material with a porosity of 50% to 70% by a single rolling process and then drying.

[0018] Furthermore, in the preparation of the negative electrode sheet:

[0019] The pressure of the first and second rolling processes is 30 to 100 Newtons;

[0020] The roll gap of the first rolling is 1.05 to 1.2 times the thickness required to achieve the compaction density of the negative electrode sheet;

[0021] The roll gap of the second rolling is 0.9 to 1.15 times the thickness required to achieve the compaction density of the negative electrode sheet;

[0022] The porosity of the dried negative electrode sheet is 32% to 39%.

[0023] Furthermore, in the preparation of the positive electrode:

[0024] The primary roller pressing pressure is 20 to 150 Newtons;

[0025] The roll gap of the first rolling process is 0.9 to 1.1 times the thickness required to achieve the compaction density of the positive electrode sheet;

[0026] The porosity of the dried positive electrode sheet is 20% to 27%.

[0027] In another aspect, the present invention provides an electrical device comprising a secondary battery as described above.

[0028] The secondary battery and its preparation method provided by this invention have the following advantages compared with the prior art:

[0029] The secondary battery provided by this invention has a negative electrode active material with a porosity of 40%–60% and a positive electrode active material with a porosity of 50%–70%; the ratio of the porosity of the negative electrode to the positive electrode is 1.2–1.8. Under these conditions, the secondary battery exhibits good pulse discharge performance and can achieve better power performance; simultaneously, the secondary battery of this invention can also achieve a high capacity retention rate at a high number of charge-discharge cycles. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of 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 only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] In the technical solution of this invention, the secondary battery includes a positive electrode and a negative electrode. In addition to the positive and negative electrode, it also includes a separator and an electrolyte, as well as a casing, a top cover, and other structures. The separator is placed between the positive and negative electrode and wound into a battery cell. The battery cell is placed inside the casing, which contains the electrolyte. The top cover seals the casing.

[0032] In some embodiments, the porosity of the negative electrode active material is 40%–60%; the porosity of the positive electrode active material is 50%–70%; and the ratio of the porosity of the negative electrode sheet to that of the positive electrode sheet is 1.2–1.8. Preferably, the ratio of the porosity of the negative electrode sheet to that of the positive electrode sheet is 1.3–1.7. More preferably, the ratio of the porosity of the negative electrode sheet to that of the positive electrode sheet is 1.4–1.7. Negative and positive electrode active materials within this porosity range can reduce mechanical damage to the negative and positive electrode active materials during rolling and reduce the occurrence of side reactions during battery charging and discharging. Controlling the ratio of the porosity of the negative and positive electrode sheets within the above range, coordinating their porosities, and achieving a reasonable ratio of negative and positive electrode sheet porosity are essential to fully realizing the battery's superior performance.

[0033] In some embodiments, the porosity of the negative electrode is 32%–39%, and the porosity of the positive electrode is 20%–27%. Preferably, the porosity of the negative electrode is 34%–37%, and the porosity of the positive electrode is 21%–25%. Porosities within these ranges effectively shorten the transport path of the secondary battery within the negative and positive electrodes, increasing the ion diffusion rate and thus improving the power and cycle performance of the secondary battery, achieving the performance requirements of fast charging, high pulse power, and long cycle life.

[0034] In some embodiments, the sum of the volumes of pores with a diameter of 100–300 nm in the positive electrode active material is 0.0025–0.03 mL / g.

[0035] In some embodiments, the sum of the volumes of pores with a diameter of 100–300 nm in the positive electrode active material is 0.006–0.028 mL / g.

[0036] In some embodiments, the sum of the volumes of pores with a diameter of 500–2000 nm in the positive electrode active material is 0.2–0.4 mL / g.

[0037] In some embodiments, the sum of the volumes of pores with a diameter of 500–2000 nm in the positive electrode active material is 0.25–0.37 mL / g.

[0038] In some embodiments, the ratio of the sum of the volumes of pores in the 100–300 nm range to the sum of the volumes of pores in the 500–2000 nm range in the positive electrode active material is 1%–10%. Pore control is mainly influenced by the preparation process. By adjusting the ammonia concentration and pH value to regulate the precursor structure, precursors with different degrees of porosity can be formed. Subsequently, by controlling the lithium ratio, temperature, and time during sintering, products with different pore distributions can be obtained.

[0039] Controlling the pore volume of the positive electrode active material is beneficial for the electrolyte to fully wet the positive electrode active material, so that the battery capacity can be better utilized.

[0040] In some embodiments, the compaction density of the negative electrode sheet is 1.0–1.5 g / cc. Within the scope of this invention, the compaction density of the negative electrode sheet can increase the discharge capacity of the secondary battery, reduce internal resistance, reduce polarization, and extend the cycle life of the secondary battery.

[0041] In some embodiments, the compaction density of the positive electrode sheet is 2.5–3.3 g / cc. Within the scope of this invention, the compaction density of the positive electrode sheet can increase the discharge capacity of the secondary battery, reduce internal resistance, reduce polarization, and extend the cycle life of the secondary battery.

[0042] In some embodiments, the preparation method of a secondary battery includes the preparation of a negative electrode active material and the preparation of a positive electrode active material.

[0043] In some embodiments, the preparation of the negative electrode active material includes heat treatment, graphitization, and carbon coating of a graphite precursor to obtain a negative electrode active material with a porosity of 40% to 60%. In some embodiments, the graphite precursor includes at least one of needle coke, petroleum coke, pitch coke, or other types of coke.

[0044] In some embodiments, the heat treatment temperature in the preparation of the negative electrode active material is 300–800°C, and the time is 4–12 hours. After high-temperature heat treatment, the graphite precursor can be transformed into a three-dimensional ordered graphite structure, which is beneficial to improving the stability of the material.

[0045] In some embodiments, the graphitization temperature during the preparation of the negative electrode active material is 2400–3000°C, and the time is 20–60 h. Graphitization can promote the transformation of irregular layers of graphite precursor into ordered layers and reduce defects, which is beneficial to improving the electronic conductivity of the material.

[0046] In some embodiments, the surface coating of the negative electrode active material comprises a carbon material.

[0047] In some embodiments, the carbon coating layer is carbonized at a temperature of 800–1800°C for a time of 12–30 hours. Forming a uniform carbon coating layer on the surface of the negative electrode active material can improve the compatibility between the negative electrode material and the electrolyte, prevent the co-intercalation and decomposition of organic solvents, and avoid the peeling off of the graphite structure during cyclic charging and discharging.

[0048] In some embodiments, the coating raw materials used in the preparation of the negative electrode active material include at least one of phenolic resin, furfuryl alcohol resin, epoxy resin, polyurethane, and saccharide organic compounds.

[0049] In some embodiments, the positive electrode active material comprises a ternary material.

[0050] In some embodiments, the positive electrode active material comprises lithium nickel cobalt manganese oxide. In some embodiments, the positive electrode active material comprises a material with the chemical formula Li x Ni y Co z Mn k M p A compound of O2, wherein M contains at least one of Y, Nb, In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, Cr or Fe, and 0.8≤x≤1.2, 0<y<1, 0<z<1, 0<k<1, 0≤p≤0.1.

[0051] In some embodiments, the preparation of the positive electrode active material includes a first sintering of a ternary precursor material, a doped raw material and a lithium source to obtain an intermediate product, and a second sintering of the intermediate product with a coating raw material to obtain a positive electrode active material with a porosity of 50% to 70%.

[0052] In some embodiments, in the preparation of the positive electrode active material, the ternary material precursor includes nickel cobalt manganese oxide, and the doping raw material and coating raw material include at least one of zinc oxide, zirconium oxide, aluminum oxide, molybdenum oxide, niobium oxide, and tungsten oxide.

[0053] In some embodiments, the first sintering temperature in the preparation of the positive electrode active material is 600–1000°C, and the time is 4–24 h. The second sintering temperature is 400–600°C, and the time is 2–12 h. The first sintering temperature is higher than the second sintering temperature. The higher temperature is conducive to the opening of grain boundaries in the crystal structure of the ternary material, promoting the incorporation of dopant elements. At a lower temperature, it is conducive to the tight coating of the coating material on the surface of the ternary material, reducing the structural collapse and dissolution of the ternary material.

[0054] In some embodiments, the method for preparing a secondary battery further includes the preparation of a negative electrode and a positive electrode.

[0055] The preparation of the negative electrode sheet includes covering the negative electrode slurry of the negative electrode active material onto the surface of the negative electrode current collector, performing a first rolling and a second rolling, and then drying;

[0056] The porosity of the dried negative electrode sheet is 32% to 39%.

[0057] The preparation of the positive electrode sheet includes coating the positive electrode slurry of the positive electrode active material onto the surface of the positive electrode current collector with a single rolling press and then drying. In this invention, the compaction density of the negative electrode sheet is less than that of the positive electrode sheet. If the negative electrode sheet is only rolled once, the degree of breakage of the negative electrode particles will be increased, which is not conducive to improving the performance of the material.

[0058] In some embodiments, during the step of forming the negative electrode sheet, the pressure of the first rolling and the second rolling is 30 to 100 Newtons, specifically, it can be 30, 40, 50, 60, 70, 80, 90, 100 Newtons or any combination thereof.

[0059] In some embodiments, during the preparation of the negative electrode sheet, the roll gap in the first rolling process is 1.05 to 1.2 times the thickness required to achieve the compaction density of the negative electrode sheet. The roll gap in the second rolling process is 0.9 to 1.15 times the thickness required to achieve the compaction density of the negative electrode sheet. During rolling, the size of the roll gap is adjusted according to the thickness of the negative electrode sheet when the set compaction density is achieved. This ensures that the electrode sheet compaction density is maintained while obtaining an electrode sheet of suitable thickness, which is beneficial to the interaction between the electrode sheet and the electrolyte, thus ensuring the power and cycle performance of the secondary battery.

[0060] In some embodiments, the porosity of the dried negative electrode sheet is 32% to 39%.

[0061] In some embodiments, during the preparation of the positive electrode sheet, the primary rolling pressure is 20 to 150 Newtons. Specifically, the rolling pressure can be 20, 50, 70, 90, 120, 150 Newtons, or any combination thereof. In some embodiments, during the preparation of the positive electrode sheet, the roll gap during the primary rolling is 0.9 to 1.1 times the thickness required to achieve the compaction density of the positive electrode sheet.

[0062] In some embodiments, the porosity of the dried positive electrode sheet is 20% to 27%.

[0063] In some embodiments, the viscosity of the negative electrode slurry is 2000–4000 mPa·s, and the solid content is 40–50%.

[0064] In some embodiments, the viscosity of the positive electrode slurry is 3000–6000 mPa·s, and the solid content is 50–65%.

[0065] The solid content of the positive and negative electrode slurries is closely related to their stability. Within the range specified in this invention, a higher solid content in the slurry is beneficial for reducing stirring time and improving coating and drying efficiency. Within the range specified in this invention, the viscosity and solid content of the slurry are conducive to slurry stability, improving production efficiency and reducing equipment wear and tear.

[0066] In some embodiments, the negative electrode slurry further comprises a negative electrode conductive agent, a negative electrode binder, and a thickener; the positive electrode slurry further comprises a positive electrode conductive agent and a positive electrode binder.

[0067] In some embodiments, the negative electrode conductive agent may specifically include at least one of conductive carbon black, carbon fiber, acetylene black, Ketjen black, graphene, or carbon nanotubes; the negative electrode binder may specifically include at least one of sodium carboxymethyl cellulose, polypropylene, polyethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, or polyhexafluoropropylene; and the thickener may include at least one of styrene-butadiene rubber latex, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, or casein.

[0068] In some embodiments, the negative electrode conductive agent is selected from conductive carbon black, the negative electrode binder is selected from sodium carboxymethyl cellulose, and the thickener is selected from styrene-butadiene rubber emulsion; and by mass, the negative electrode active material layer includes 92-97 parts of graphite, 1-2.5 parts of conductive carbon black, 1-1.5 parts of sodium carboxymethyl cellulose, and 1-3 parts of styrene-butadiene rubber emulsion.

[0069] In some embodiments, the positive electrode active material may include lithium nickel cobalt manganese oxide, the positive electrode conductive agent may include at least one of conductive carbon black, carbon fiber, acetylene black, Ketjen black, graphene or carbon nanotubes, and the positive electrode binder may include at least one of polypropylene, polyethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene or polyhexafluoropropylene.

[0070] Specifically, in some embodiments, the positive electrode active material is specifically selected as lithium nickel cobalt manganese oxide, the positive electrode conductive agent is selected as conductive carbon black, and the positive electrode binder is selected as polyvinylidene fluoride; and by mass, the positive electrode active material layer includes 90-95 parts of lithium nickel cobalt manganese oxide, 4-6 parts of conductive carbon black, and 2-6 parts of polyvinylidene fluoride.

[0071] In some embodiments of the present invention, an electrical device is also provided, comprising the aforementioned secondary battery.

[0072] The following description is based on specific embodiments.

[0073] Example 1:

[0074] (1) Preparation of the first negative electrode active material (-Ⅰ):

[0075] Under inert gas protection, needle coke was heat-treated at 600℃ for 8 hours, and then graphitized at 2500℃ for 30 hours. The resulting intermediate product was then carbonized with phenolic resin under inert gas protection at 1000℃ for 15 hours to obtain the negative electrode active material.

[0076] (2) Preparation of the first positive electrode active material (+Ⅰ):

[0077] Ni 0.5 Co 0.2 Mn 0.3 (OH)₂, lithium hydroxide, and zinc oxide were sintered for the first time at a molar ratio of 1:1.09:0.0055 at 800℃ for 12 hours to obtain an intermediate product. The intermediate product was then sintered with zirconium oxide at a molar ratio of 1:0.0055 for the second time at 450℃ for 8 hours to obtain the positive electrode active material.

[0078] (3) Preparation of negative electrode:

[0079] Using the first negative electrode active material (-Ⅰ) as the negative electrode active material, conductive carbon black as the negative electrode conductive agent, sodium carboxymethyl cellulose as the negative electrode binder, and styrene-butadiene rubber latex as the thickener, 95 parts by weight of the negative electrode active material, 1.5 parts by weight of conductive carbon black, 1.5 parts by weight of sodium carboxymethyl cellulose, and 2 parts by weight of styrene-butadiene rubber latex were pre-mixed at low speed, and water was added to prepare a mixture with a solid content of 60%. The mixture was then dispersed at high speed for 4 hours, and water was added to adjust the viscosity, resulting in a negative electrode slurry with a viscosity of 2890 mPa·s and a solid content of 43.5%. Copper foil was then selected as the negative electrode current collector. The negative electrode slurry was coated onto the surface of the negative electrode current collector and dried. After drying, a first rolling press was performed at a pressure of 50 Newtons, with the roll gap being 1.1 times the thickness required to achieve the compaction density of the negative electrode sheet. A second rolling process is then performed with a pressure of 70 Newtons, and the roll gap is 1 times the thickness required to achieve the compaction density of the negative electrode sheet.

[0080] (4) Preparation of the positive electrode:

[0081] The first positive electrode active material (+Ⅰ) was selected as the positive electrode active material. 92 parts by weight of the positive electrode active material, 5 parts by weight of conductive carbon black, and 3 parts by weight of polyvinylidene fluoride were pre-mixed at low speed, and N-methylpyrrolidone was added to prepare a mixture with a solid content of 70%. Then, the mixture was dispersed at high speed for 4 hours, and N-methylpyrrolidone was added to adjust the viscosity, resulting in a positive electrode slurry with a viscosity of 4180 mPa·s and a solid content of 56.5%. Subsequently, aluminum foil was selected as the positive electrode current collector. The positive electrode slurry was coated onto the surface of the positive electrode current collector and dried. After drying, it underwent a single rolling press at a pressure of 100 Newtons, with the roll gap being 0.95 times the thickness required to achieve the compacted density of the positive electrode sheet.

[0082] After obtaining the above-mentioned positive and negative electrode sheets, a secondary battery is prepared based on the above-mentioned positive and negative electrode sheets.

[0083] Specifically, firstly, the positive and negative electrode plates are cut and shaped.

[0084] Subsequently, the separator is placed between the cut positive and negative electrode sheets and wound to obtain the battery cell. At the same time, the separator can be a PE base film with a thickness of 12μm, and a ceramic with a thickness of 4μm is coated on one side of the PE base film. The porosity of the separator is 42.36%, and the air permeability of the separator is 126s / 100mL.

[0085] Finally, the battery cell is placed into the casing, and electrolyte is injected. The casing is then sealed with a top cover, thus obtaining the secondary battery of this embodiment. The electrolyte in this step includes lithium salt, organic solvent, and electrolyte additives. The lithium salt is a mixture of 1.2 mol LiPF6 and LiFSI; the organic solvent can be a mixture of EC:DMC:EMC = 1:1:1 (volume ratio).

[0086] The preparation methods for the remaining embodiments and comparative examples are the same as those in Example 1, and the specific proportions are shown in Tables 1 to 3.

[0087] Table 1 Parameters of the negative electrode active material

[0088]

[0089]

[0090] Table 2 Parameters of the positive electrode active material

[0091]

[0092]

[0093] Table 3. Parameters of the Examples and Comparative Examples and the Performance of Their Secondary Batteries

[0094]

[0095]

[0096]

[0097]

[0098]

[0099] As shown in Table 3, comparing Examples 1-9 with Comparative Example 1, it is evident that when the porosity of the negative electrode active material is 40%-60% and the porosity of the positive electrode active material is 50%-70%, the porosity of the negative electrode sheet can be well maintained at 32%-39%, and the porosity of the positive electrode sheet at 20%-27%, thus ensuring a porosity ratio of 1.2-1.8 between the negative and positive electrode sheets. Maintaining the porosity of both the positive and negative electrode active materials at suitable levels is beneficial for improving the discharge and cycle performance of the secondary battery.

[0100] As can be seen from the comparison between Examples 1 and Examples 2-3, the porosity of the negative electrode sheet first increases and then decreases with the increase of the first and second rolling pressure. Specifically, the secondary battery performance is better when the first rolling pressure is set to 50 Newtons and the second rolling pressure is set to 70 Newtons. This is because rolling pressures exceeding the range of this invention can easily cause large-area breakage of the negative electrode particles, while rolling pressures below the range of this invention result in a loose connection between the negative electrode sheet and materials such as binders and conductive agents. During long-term cyclic charging and discharging, this can easily cause the negative electrode active material to detach.

[0101] In summary, the secondary battery provided by this invention, and the secondary battery prepared according to the method of this invention, has a negative electrode active material with a porosity of 40%–60%, a positive electrode active material with a porosity of 50%–70%, a negative electrode sheet with a porosity of 32%–39%, a positive electrode sheet with a porosity of 20%–27%, and a porosity ratio of the negative electrode sheet to the positive electrode sheet of 1.2–1.8. Under these conditions, the secondary battery exhibits better pulse release performance at low temperatures, resulting in better power performance. Furthermore, the secondary battery of this invention can achieve a high capacity retention rate at a high number of charge-discharge cycles, thereby achieving a longer service life.

[0102] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0103] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A secondary battery, characterized in that, It includes negative electrode sheets containing negative electrode active materials and positive electrode sheets containing positive electrode active materials; The porosity of the negative electrode active material is 43%–56%; The porosity of the positive electrode active material is 53%–65%; The porosity ratio of the negative electrode to the positive electrode is 1.4 to 1.

7.

2. The secondary battery according to claim 1, characterized in that, The porosity of the negative electrode is 32% to 39%; the porosity of the positive electrode is 20% to 27%.

3. The secondary battery according to claim 1, characterized in that, The positive electrode active material includes Li x Ni y Co z Mn k M p A compound of O2, wherein M contains at least one of Y, Nb, In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, Cr or Fe, and 0.8≤x≤1.2, 0<y<1, 0<z<1, 0<k<1, 0≤p≤0.

1.

4. The secondary battery according to claim 1, characterized in that, The porosity of the positive electrode active material satisfies at least one of the following characteristics: (a) The sum of the volumes of pores of 100–300 nm in the positive electrode active material is 0.0025–0.03 mL / g; (b) The sum of the volumes of pores of 500–2000 nm in the positive electrode active material is 0.2–0.4 mL / g; (c) The ratio of the sum of the volumes of pores of 100–300 nm to the sum of the volumes of pores of 500–2000 nm in the positive electrode active material is 1%–10%.

5. The secondary battery according to claim 1, characterized in that, The compaction density of the negative electrode sheet is 1.0 to 1.5 g / cc.

6. The secondary battery according to claim 1, characterized in that, The compaction density of the positive electrode is 2.5–3.3 g / cc.

7. The secondary battery according to claim 1, characterized in that, The surface of the negative electrode active material has a coating layer, which includes a carbon material.

8. A method for preparing a secondary battery as described in claim 1, characterized in that, The method for preparing the secondary battery further includes: Preparation of negative electrode and preparation of positive electrode; The preparation of the negative electrode sheet includes covering the surface of the negative electrode current collector with a negative electrode slurry of negative electrode active material with a porosity of 43% to 56%, performing a first roll pressing and a second roll pressing, and then drying; The preparation of the positive electrode sheet includes coating the surface of the positive electrode current collector with a positive electrode slurry containing a positive electrode active material with a porosity of 53% to 65% by a single rolling process and drying. After drying, the porosity ratio of the negative electrode sheet to the positive electrode sheet is 1.4 to 1.

7.

9. The method for preparing a secondary battery according to claim 8, characterized in that, In the preparation of the negative electrode sheet: The pressure of the first and second rolling processes is 30 to 100 Newtons; The roll gap of the first rolling is 1.05 to 1.2 times the thickness required to achieve the compaction density of the negative electrode sheet; The roll gap of the second rolling is 0.9 to 1.15 times the thickness required to achieve the compaction density of the negative electrode sheet; The porosity of the dried negative electrode sheet is 32% to 39%.

10. The method for preparing a secondary battery according to claim 8, characterized in that, In the preparation of the positive electrode: The primary rolling pressure is 20 to 150 Newtons; the roll gap of the primary rolling is 0.9 to 1.1 times the thickness required to achieve the compaction density of the positive electrode sheet; The porosity of the dried positive electrode sheet is 20% to 27%.

11. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1 to 7.

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