Negative electrode material, secondary battery, and electric device

Abstract

The application discloses a negative electrode material, a secondary battery and an electric device. The negative electrode material comprises a core, the core comprises a first manganese oxide, and an outer surface of the core is provided with a shell layer, the shell layer comprises a conductive material and a second manganese oxide. The shell layer with the conductive material and the second manganese oxide is coated on the first manganese oxide, so that the mechanical property, the conductive property and the stability of the negative electrode material are improved, and the cycle performance and the rate performance of the battery are improved.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, specifically to a negative electrode material, a secondary battery, and an electrical device. Background Technology

[0002] With the adjustment of the world's energy structure and the increasing popularity of electric vehicles, society has higher and higher requirements for the performance of lithium-ion batteries. However, traditional graphite anode materials are limited by their theoretical capacity and cannot meet the new requirements for lithium-ion batteries. Therefore, the development of new high-performance anode materials is of great significance.

[0003] Manganese-based anode materials possess high specific capacity and superior cycle performance compared to traditional Si-based materials, indicating significant application potential. However, manganese-based anode materials are prone to volume expansion during cycling, leading to rapid capacity decay and material agglomeration, severely impacting their cycle performance. Furthermore, the conductivity of manganese-based anode materials is lower than that of traditional graphite anodes, affecting battery rate performance. Therefore, suppressing volume expansion and improving conductivity of manganese-based anode materials to enhance battery cycle and rate performance are pressing technical challenges that need to be addressed. Summary of the Invention

[0004] The purpose of this application is to provide a negative electrode material, a secondary battery, and an electrical device. This application improves the mechanical properties, conductivity, and stability of the negative electrode material by coating a first manganese oxide with a shell containing a conductive material and a second manganese oxide, thereby enhancing the battery's cycle performance and rate capability, and solving the aforementioned technical problems.

[0005] In view of this, this application provides a negative electrode material, including a core comprising a first manganese oxide, and a shell comprising a conductive material and a second manganese oxide on the surface of the core.

[0006] In some embodiments, the first manganese oxide and the second manganese oxide have oxygen vacancies.

[0007] In some embodiments, the conductive material includes a first carbon material and a second carbon material, wherein the first carbon material includes at least one of graphene and graphene oxide.

[0008] In some embodiments, the shell has an inner layer, an intermediate layer, and an outer layer, wherein the inner layer comprises the first carbon material, the intermediate layer comprises the second manganese oxide, and the outer layer comprises the second carbon material.

[0009] In some embodiments, the first manganese oxide comprises MnO x The second manganese oxide includes MnO y, where 0 < x ≤ 2, 0 < x ≤ 2, and x ≥ y.

[0010] In some embodiments, the mass ratio of the first manganese oxide, the first carbon material, the second manganese oxide, and the second carbon material is (1-2):(0.1-1):(0.2-2):(0-2).

[0011] In some embodiments, the second carbon material includes at least one of amorphous carbon, mesophase carbon microspheres, natural graphite, hard carbon, activated carbon, highly oriented graphite, carbon black, and carbon nanotubes.

[0012] In some embodiments, the thickness of the shell layer is 30–100 nm.

[0013] In some embodiments, the Dv50 of the negative electrode material is 5–20 μm.

[0014] In some embodiments, the average particle size of the first manganese oxide is larger than that of the second manganese oxide.

[0015] Accordingly, this application also provides a secondary battery, including the aforementioned negative electrode material.

[0016] Accordingly, this application also provides an electrical device, including the aforementioned secondary battery. The secondary battery serves as the power supply for the electrical device.

[0017] The beneficial effects of this application are as follows: Compared with the prior art, the negative electrode material of this application includes a core comprising a first manganese oxide, and a shell layer on the outer surface of the core comprising a conductive material and a second manganese oxide. The conductive material of this application can improve the conductivity of the negative electrode material. Simultaneously, the conductive material is selected from a first carbon material and / or a second carbon material, which can effectively absorb the stress generated by the volume expansion of the manganese oxide, weakening the pulverization phenomenon of the negative electrode material. The presence of the shell layer can also prevent the first manganese oxide from agglomerating, causing material deactivation or separation from the binder, thus improving the cycle stability of the material. This application, through a multi-layered coating structure and the creation of oxygen vacancies, reduces MnO... x While agglomerating, alleviating volume expansion, and improving the conductivity of materials, the oxygen vacancies formed can also improve the electrochemical performance of the material system. This is because oxygen vacancies can provide a large number of active sites for lithium ion insertion and extraction, thereby improving the mechanical properties, conductivity, and stability of the anode material, and enhancing the cycle performance and rate performance of the battery. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 SEM images of the negative electrode material prepared in Example 1;

[0020] Figure 2 The capacity retention curve of the secondary battery in Example 1 at a temperature of 25°C and a charge / discharge rate of 1C / 1C is shown. Detailed Implementation

[0021] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In addition, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc. are used only as illustrative purposes and do not impose numerical requirements or establish an order. Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and conciseness and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. Additionally, whenever a range of numbers is specified in this document, it means including any referenced numbers (fractions or integers) within the range referred to.

[0022] Existing manganese-based anode materials have large capacity but poor conductivity and large volume expansion. In order to solve the problems existing in the prior art, an embodiment of this application provides an anode material, including a core, the core including a first manganese oxide, and a shell layer on the surface of the core, the shell layer including a conductive material and a second manganese oxide.

[0023] The conductive material in this embodiment enhances the conductivity of the negative electrode material and reduces its impedance. Furthermore, the shell layer on the core surface of the first manganese oxide improves the mechanical properties of the negative electrode material. When the first manganese oxide expands, it effectively binds it, reducing the expansion rate and mitigating pulverization. It also prevents excessive agglomeration of the first manganese oxide, which could lead to material deactivation or separation from the binder. The presence of the second manganese oxide maintains relatively abundant ion channels in the negative electrode material, improving its ion conduction performance, reducing polarization, and enhancing the rate performance of the material system. Therefore, this improves the stability and conductivity of the negative electrode material, thereby enhancing the battery's cycle stability, cycle life, and rate performance.

[0024] In some embodiments, the first manganese oxide and the second manganese oxide are manganese oxides with oxygen vacancies, that is, the first manganese oxide and the second manganese oxide have oxygen vacancies.

[0025] Specifically, in this embodiment, the oxygen vacancy is formed by the removal of some O atoms from the manganese oxide lattice, resulting in oxygen deficiency. The first and second manganese oxides with oxygen vacancies used in this application stabilize the crystal structure, regulate ion migration, and improve electronic conductivity. Introducing oxygen vacancies helps suppress irreversible oxygen release from the surface of the negative electrode material, slowing voltage decay. It also allows the negative electrode material to have higher lithium-ion storage capacity and more ion transport channels, effectively improving the battery's rate performance and cycle stability. In practical applications, manganese oxides can be obtained by high-temperature calcination in a system containing hydrogen or other reducing materials (such as carbon). In some specific embodiments, oxygen vacancies are determined by EPR or Raman spectroscopy using a Bruker EMX Plus electron paramagnetic resonance spectrometer. Oxygen vacancies can also be determined by XPS, thermogravimetric analysis, and other methods.

[0026] In some embodiments, the average particle size of the first manganese oxide is larger than that of the second manganese oxide, with the first manganese oxide having an average particle size between 0.5 and 6 μm and the second manganese oxide having a particle size between 10 nm and 500 nm. The smaller average particle size of the second manganese oxide compared to the first manganese oxide can improve the lithium-ion transport rate on the surface of the negative electrode material, thereby enhancing the battery's kinetic performance. Furthermore, using the aforementioned particle size ranges for both the first and second manganese oxides can further improve the overall performance of the negative electrode material and facilitate the formation of a shell layer on its surface, which is beneficial for the adsorption strength of the shell layer, thus enhancing the battery's electrochemical performance.

[0027] In some embodiments, the first manganese oxide includes MnO x The second manganese oxide includes MnO y, where 0 < x ≤ 2, 0 < x ≤ 2, and x ≥ y.

[0028] In some embodiments, x can take any value from 0.1, 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0 or a range between any two values.

[0029] In some embodiments, y takes the value of any value among 0.1, 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, and 2.0, or a range between any two values.

[0030] In some embodiments, the conductive material includes a first carbon material and a second carbon material, wherein the first carbon material includes at least one of graphene and graphene oxide (RGO). In some embodiments, the second carbon material includes at least one of amorphous carbon, mesophase carbon microspheres, natural graphite, hard carbon, activated carbon, highly oriented graphite, carbon black, and carbon nanotubes.

[0031] In some embodiments, the carbon material is amorphous carbon. Compared to graphitic carbon, due to the isotropy of amorphous carbon, lithium ions can enter the material simultaneously from all directions, thus amorphous carbon has higher ionic conductivity. Furthermore, it forms a conductive network together with graphene oxide and also acts as a buffer layer.

[0032] The first and second carbon materials mentioned above are ductile conductive materials. Due to their ductility, they can effectively absorb the stress generated by the volume expansion of manganese oxide, further reducing the expansion rate of the negative electrode material, further weakening the pulverization phenomenon of the negative electrode material, improving the stability of the negative electrode material, and further improving the cycle life of the battery.

[0033] In another embodiment, the shell has an inner layer, a middle layer, and an outer layer. The inner layer comprises a first carbon material, the middle layer comprises a second manganese oxide, and the outer layer comprises a second carbon material.

[0034] This application uses first carbon material and second carbon material as the inner and outer coating layers of the active material, which can further enhance the absorption of stress, while also constructing a stable conductive network between the negative electrode materials and preventing the materials from losing contact, thereby ensuring the stability of the overall electrochemical performance of the material.

[0035] In some embodiments, the components of the inner layer, intermediate layer, and outer layer are intermixed. Specifically, the first carbon material forms the inner layer, the second manganese oxide forms the intermediate layer on the surface of the first carbon material layer, and at least a portion of the second manganese oxide is distributed in the first carbon material layer. The second carbon material forms the outer layer on the surface of the intermediate layer, and at least a portion of the second carbon material is distributed in both the intermediate and inner layers. The negative electrode material of this application employs a multilayer structure, which can further improve the mechanical properties of the negative electrode material.

[0036] To further optimize the conductivity of the negative electrode material and reduce the expansion rate, in some embodiments, the mass ratio of the first manganese oxide, the first carbon material, the second manganese oxide, and the second carbon material is (1-2):(0.1-1):(0.2-2):(0-2).

[0037] In some embodiments, the shell thickness is 30–100 nm. A shell thickness within this range allows the negative electrode material to possess mechanical stability while ensuring that the impedance value of the negative electrode material is within a reasonable range, thereby improving the cycle performance and rate performance of the battery.

[0038] In some embodiments, the thickness of the inner layer is 5–10 nm, the thickness of the middle layer is 20–30 nm, and the thickness of the outer layer is 15–30 nm. With each layer's thickness within the above range, the conductivity and mechanical properties of the negative electrode material are reasonably balanced, thus improving the stability of the negative electrode material.

[0039] In some embodiments, the Dv50 of the negative electrode material is 5 μm to 20 μm. For example, the Dv50 of the negative electrode material can be any value from 5 μm, 8 μm, 12 μm, 15 μm, and 20 μm, or a range between any two values. Setting the Dv50 of the negative electrode material within the above range allows the negative electrode material to have a reasonable specific surface area and a shorter lithium-ion transport channel, ensuring the cycle performance and rate performance of the battery.

[0040] To further improve the electrochemical performance of the battery, in some embodiments, the particle size of the negative electrode material is as follows: Dv10 is 3-7 μm; Dv90 is 15-23 μm; Dv99 is 20-30 μm; Dv100 is 25-35 μm; and the particle size of the negative electrode material is as follows: Dn50 is 4-10 μm, Dn90 is 9-14 μm, Dn99 is 11-16 μm, and Dn100 is 15-25 μm.

[0041] This application also provides a method for preparing the above-mentioned negative electrode material, including the following steps:

[0042] S1. Disperse the first manganese oxide and the conductive agent evenly in the first solvent, and obtain a mixed solution A after filtration;

[0043] S2. Add manganese salt to solution A, and after dissolving the manganese salt, obtain mixture B;

[0044] S3. Add oxidant to mixture B. After the reaction is complete, filter to obtain solid substance.

[0045] S4. Sinter the solid material to obtain the negative electrode material.

[0046] Through the above steps, a negative electrode material with a shell coating a first manganese oxide surface can be obtained, wherein the shell includes a conductive agent and a second manganese oxide to improve the mechanical and electrical properties of the negative electrode material. In step S3, the addition of an oxidant oxidizes the manganese salt, converting it into a second manganese oxide, which is then adsorbed onto the surface of the first manganese oxide. The oxidant includes hydrogen peroxide. In some embodiments, the conductive agent includes one or more of graphene and graphene oxide. The manganese salt includes at least one of potassium permanganate (KMnO4), manganese oxalate, and manganese acetate.

[0047] In some embodiments, in step S3, an oxidant is added to the mixture B. After the reaction is complete, the method further includes adding a carbon source to the reaction solution. In this embodiment, the carbon source includes at least one of glucose, phenolic resin, epoxy resin, CTAB, phthalimide, aniline, cellulose, polyethylene glycol, organic biomass materials, and polyvinylidene fluoride. The addition of the carbon source results in a second carbon material layer coating the surface of the negative electrode material obtained after sintering. This second carbon material layer not only has electrical conductivity but also alleviates the expansion of the negative electrode material. During the sintering process, the formed carbon material can also in situ abstract oxygen atoms from the first manganese oxide and the second manganese oxide, thereby creating first and second manganese oxides with oxygen vacancies, further improving the performance of the negative electrode material.

[0048] In some embodiments, step S4 includes:

[0049] S41. After freeze-drying the solid material, perform the first high-temperature sintering under a protective atmosphere. The temperature of the first high-temperature sintering is 200-700℃, and the time of the first high-temperature sintering is 2-8 hours.

[0050] S42. Perform a second high-temperature sintering on the material sintered in the first sintering. The temperature of the second high-temperature sintering is 500-1000℃, and the time of the second high-temperature sintering is 4-12 hours.

[0051] In some embodiments, the heating rate for the first and second high-temperature sintering is 5–20 °C / min, and the pressure is 90 Pa–121 KPa. After the reaction is completed, the material is naturally cooled to room temperature to obtain the negative electrode material.

[0052] In some embodiments, the high-temperature sintering equipment can be a vacuum tube furnace, a vacuum resistance furnace, a vacuum muffle furnace, a hot-wire CVD, or similar equipment.

[0053] In some embodiments, the protective atmosphere during the high-temperature sintering process is one or more of nitrogen, argon, and helium.

[0054] The anode material preparation method of this application uses readily available raw materials and does not involve the large-scale use of strong acids and alkalis, resulting in minimal environmental pollution, simple process, and low cost.

[0055] This application also provides a secondary battery, which includes a negative electrode comprising the aforementioned negative electrode material. Because the secondary battery includes the aforementioned negative electrode material, and because the negative electrode material has excellent conductivity and stability, it can affect the performance of the secondary battery, particularly improving the cycle performance and rate capability, thus giving the secondary battery superior cycle life and safety.

[0056] In some embodiments, the preparation of a secondary battery includes: assembling a positive electrode, a negative electrode, a separator, and other battery components, and then performing processes such as shaping, baking, packaging, liquid injection, formation, and capacity testing to obtain a secondary battery. The battery types include pouch, cylindrical, and aluminum-cased batteries.

[0057] This application provides an electrical device that includes the aforementioned secondary battery. The electrical device can be used in, but is not limited to, backup power supplies, motors, electric vehicles, electric motorcycles, electric bicycles, bicycles, power tools, and large household storage batteries.

[0058] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0059] Example 1

[0060] Preparation of negative electrode materials

[0061] 1) 1g of MnO2 powder (average particle size of 2μm) and 0.15g of graphene (GR) were placed in deionized water and ultrasonically dispersed to obtain mixed solution A;

[0062] 2) Add 1.5g of potassium permanganate powder to mixed solution A and stir until the potassium permanganate is completely dissolved to obtain solution B;

[0063] 3) Add 20 mL of 2% hydrogen peroxide solution to solution B while stirring. After reacting for 6 hours, add 0.8 g of phenolic resin, mix and stir for 1 hour, sonicate for 20 minutes, repeat twice, and then filter to obtain filter residue C.

[0064] 4) After drying the filter residue C, place it in a vacuum tube furnace and carbonize it at 400℃ for 4 hours under a nitrogen atmosphere. Then, raise the temperature to 650℃ and sinter for 8 hours. The heating rate is 5℃ / min and the pressure is 101KPa. After the reaction is completed, allow it to cool naturally to room temperature.

[0065] 5) The cooled sintered product was pulverized by a pulverizer and then sieved to obtain a negative electrode material with a Dv50 of 12μm and a core-shell structure. The negative electrode material has oxygen vacancies. The core layer of the negative electrode material is MnO2 with an average particle size of 2μm. The shell layer includes graphene, amorphous carbon, and MnO2 with an average particle size of 200nm. Graphene is attached to the surface of the core layer as the inner layer of the shell. MnO2 with an average particle size of 200nm is attached to the surface of the graphene as the middle layer of the shell. Amorphous carbon is attached to the surface of the middle layer as the outer layer of the shell. The thickness of the shell layer is 50nm. The mass ratio of the first manganese oxide MnO2, graphene oxide (graphene RG is oxidized to graphene oxide RGO after high-temperature sintering), the second manganese oxide MnO2 (the second manganese oxide MnO2 is generated after hydrogen peroxide reacts with potassium permanganate) and amorphous carbon in the negative electrode material is 1:0.1:0.8:0.8.

[0066] Example 2

[0067] The preparation method of the negative electrode material is the same as that in Example 1. The difference is that the power of the pulverizer is changed in step 5 to obtain a Dv50 of 5μm for the negative electrode material.

[0068] Example 3

[0069] The preparation method of the negative electrode material is the same as that in Example 1. The difference is that the power of the pulverizer is changed in step 5 to obtain a Dv50 of 8μm for the negative electrode material.

[0070] Example 4

[0071] The preparation method of the negative electrode material is the same as that in Example 1. The difference is that the power of the pulverizer is changed in step 5 to obtain a Dv50 of 15μm for the negative electrode material.

[0072] Example 5

[0073] The preparation method of the negative electrode material is the same as that in Example 1. The difference is that the power of the pulverizer is changed in step 5 to obtain a Dv50 of 20μm for the negative electrode material.

[0074] Example 6

[0075] The method for preparing the negative electrode material is the same as in Example 1. The difference is that the pressure of the vacuum tube furnace is changed in step 4, and the shell thickness of the obtained negative electrode material is 30 nm.

[0076] Example 7

[0077] The method for preparing the negative electrode material is the same as in Example 1. The difference is that the pressure of the vacuum tube furnace is changed in step 4, and the shell thickness of the obtained negative electrode material is 70 nm.

[0078] Example 8

[0079] The method for preparing the negative electrode material is the same as in Example 1. The difference is that the pressure of the vacuum tube furnace is changed in step 4, and the shell thickness of the obtained negative electrode material is 90 nm.

[0080] Example 9

[0081] The method for preparing the negative electrode material is the same as in Example 1. The difference is that the pressure of the vacuum tube furnace is changed in step 4, and the shell thickness of the obtained negative electrode material is 100 nm.

[0082] Example 10

[0083] The preparation method of the negative electrode material is the same as that in Example 1. The difference is that the amount of MnO2 powder, graphene, potassium permanganate powder and phenolic resin added in steps 1 to 3 is adjusted so that the ratio of the first manganese oxide MnO2, graphene oxide, the second manganese oxide and amorphous carbon in the obtained negative electrode material is 1:0.5:0.2:2.

[0084] Example 11

[0085] The preparation method of the negative electrode material is the same as that in Example 1. The difference is that the amount of MnO2 powder, graphene, potassium permanganate powder and phenolic resin added in steps 1 to 3 is adjusted so that the ratio of the first manganese oxide MnO2, graphene oxide, the second manganese oxide and amorphous carbon in the obtained negative electrode material is 1.5:0.8:2:0.17.

[0086] Example 12

[0087] The preparation method of the negative electrode material is the same as that in Example 1. The difference is that the amount of MnO2 powder, graphene, potassium permanganate powder and phenolic resin added in steps 1 to 3 is adjusted so that the ratio of the first manganese oxide MnO2, graphene oxide, the second manganese oxide and amorphous carbon in the obtained negative electrode material is 1.8:1:1.5:0.1.

[0088] Example 13

[0089] The preparation method of the negative electrode material is the same as that in Example 1. The difference is that the amount of MnO2 powder, graphene, potassium permanganate powder and phenolic resin added in steps 1 to 3 is adjusted so that the ratio of the first manganese oxide MnO2, graphene oxide, the second manganese oxide and amorphous carbon in the obtained negative electrode material is 2:0.3:0.5:0.6.

[0090] Example 14

[0091] The preparation method of the negative electrode material is the same as that in Example 1, except that the particle size of the added manganese dioxide in step 1 is 0.5 μm.

[0092] Example 15

[0093] The preparation method of the negative electrode material is the same as that in Example 1, except that the particle size of the added manganese dioxide in step 1 is 3 μm.

[0094] Example 16

[0095] The preparation method of the negative electrode material is the same as that in Example 1, except that the particle size of the added manganese dioxide in step 1 is 5 μm.

[0096] Example 17

[0097] The preparation method of the negative electrode material is the same as that in Example 1, except that the particle size of the added manganese dioxide in step 1 is 6 μm.

[0098] Examples 18-23

[0099] The preparation method of the negative electrode material is the same as that in Example 1. The difference is that in step 3, the stirring speed is adjusted to obtain MnO2 with different average particle sizes in the shell layer.

[0100] Comparative Example 1

[0101] Uncoated manganese dioxide (particle size 2μm) was used directly as the negative electrode material.

[0102] Comparative Example 2

[0103] The preparation method of the negative electrode material is the same as that in Example 1. The difference is that graphene is not added in step 1 and phenolic resin is not added in step 3. That is, the negative electrode material does not have conductive material.

[0104] The negative electrode materials prepared in Examples 1-20 and the negative electrode materials prepared in Comparative Examples 1-2 were used to prepare secondary batteries using the following method:

[0105] Method for preparing positive electrode sheet: Lithium iron phosphate, conductive carbon black and PVDF are mixed in a weight ratio of 95:1.5:3.5, dissolved in NMP, and after being mixed evenly, they are coated on both sides of carbon-coated aluminum foil. Then the electrode sheet is dried, rolled, slit and cut to obtain positive electrode sheet; the thickness of positive electrode sheet is 115±3μm.

[0106] Preparation method of negative electrode sheet: Add negative electrode material, conductive carbon black, CMC and SBR in water at a weight ratio of 94:1:1:3 and mix thoroughly. After mixing evenly, coat both sides of the mixture onto copper foil. Then dry, roll, slit and cut the electrode sheet to obtain the negative electrode sheet.

[0107] Diaphragm: Polyethylene membrane;

[0108] Electrolyte: Ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were mixed in a 1:1:1 volume ratio. In an argon-atmosphere glove box with a water content of <10 ppm, thoroughly dried lithium hexafluorophosphate was dissolved in the above organic solvent to prepare a 1 mol / L lithium hexafluorophosphate solution. The solution was mixed thoroughly to obtain the electrolyte.

[0109] The positive electrode, negative electrode, separator and other battery components prepared in this application are assembled and subjected to processes such as shaping, baking, packaging, liquid injection, formation and capacity testing to obtain a lithium iron phosphate soft-pack lithium-ion battery.

[0110] Performance testing

[0111] 1) Capacity retention rate and battery rate performance test: The nominal capacity of the secondary battery is C1. At 25±5℃, the battery is subjected to charge and discharge cycles at 1C / 1C, 3C / 3C, and 5C / 5C currents respectively. The charging cut-off voltage is 4.35V and the discharging cut-off voltage is 2.75V. After 200 cycles, the discharge capacity C2 is recorded. Capacity retention rate = C2 / C1×100%.

[0112] 2) Negative electrode expansion rate test method:

[0113] First, take the negative electrode sheet after rolling and measure its thickness, and take the average value d1. Then, disassemble the battery after cycling (at a temperature of 25±5℃, after 200 cycles of 1C / 1C charge and discharge) and measure the thickness of the negative electrode sheet, and take the average value d2. The copper foil thickness is d0, and the expansion rate is 100%*(d2-d1) / (d1-d0).

[0114] Table 1. Parameters and performance test results of the anode materials prepared in Examples 1-23 and Comparative Examples 1-2.

[0115]

[0116]

[0117]

[0118] Results analysis:

[0119] Compared with Comparative Examples 1 and 2, the cycle performance and rate performance of Examples 1 to 23 are significantly improved, indicating that the negative electrode material can greatly improve the electrochemical performance of the battery. This is because the negative electrode material of this application has a coating setting, and the coating layer has a conductive material and a second manganese oxide, which are all beneficial to the improvement of the battery's electrochemical performance. By comparing the data of Examples 1 with Examples 2 to 5, it was found that under the condition of fixed proportions of each component in the material system, the battery with a negative electrode material Dv50 in the range of 5 to 20 μm has better cycle performance and rate performance.

[0120] As can be seen from the test data of Examples 1 and 23, introducing oxygen vacancies into the negative electrode material can improve the cycle stability and rate performance of the battery.

[0121] This application provides a negative electrode material, a secondary battery, and an electrical device. The negative electrode material includes a core comprising a first manganese oxide, and an outer shell comprising a conductive material and a second manganese oxide. The conductive material improves the conductivity of the negative electrode material. Furthermore, the conductive material, selected from a first carbon material and / or a second carbon material, effectively absorbs the stress generated by the volume expansion of the manganese oxide, reducing the pulverization of the negative electrode material. The presence of the shell also prevents the first manganese oxide from agglomerating, causing material deactivation or separation from the binder, thus improving the cycle stability of the material. This application, through a multi-layered coating structure and the creation of oxygen vacancies, reduces MnO... x While agglomerating, alleviating volume expansion, and improving the conductivity of materials, the oxygen vacancies formed can also improve the electrochemical performance of the material system. This is because oxygen vacancies can provide a large number of active sites for lithium ion insertion and extraction, thereby improving the mechanical properties, conductivity, and stability of the anode material, and enhancing the cycle performance and rate performance of the battery.

[0122] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0123] The above provides a detailed description of a negative electrode material, a secondary battery, and an electrical device provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A negative electrode material, characterized in that, The device includes a core comprising a first manganese oxide, and a shell comprising a conductive material and a second manganese oxide on its surface; the conductive material comprises a first carbon material and a second carbon material. The first manganese oxide includes MnO x The second manganese oxide includes MnO y Where 0 < x ≤ 2, 0 < y ≤ 2, x ≥ y; the first manganese oxide and the second manganese oxide have oxygen vacancies; The shell has an inner layer and an outer layer, the inner layer comprising the first carbon material and the outer layer comprising a second carbon material; The first carbon material includes at least one of graphene and graphene oxide; The second carbon material includes at least one of amorphous carbon, mesophase carbon microspheres, natural graphite, hard carbon, highly oriented graphite, and carbon nanotubes.

2. The negative electrode material according to claim 1, characterized in that, The shell also has an intermediate layer, which includes the second manganese oxide.

3. The negative electrode material according to claim 1, characterized in that, The mass ratio of the first manganese oxide, the first carbon material, the second manganese oxide, and the second carbon material is (1~2): (0.1~1): (0.2~2): (0~2).

4. The negative electrode material according to claim 1, characterized in that, The thickness of the shell layer is 30-100 nm; the thickness of the inner layer is 5-10 nm; and the thickness of the outer layer is 15-30 nm.

5. The negative electrode material according to claim 1, characterized in that, The Dv50 of the negative electrode material is 5~20μm.

6. The negative electrode material according to any one of claims 1 to 5, characterized in that, The average particle size of the first manganese oxide is larger than that of the second manganese oxide.

7. A secondary battery, characterized in that, Includes the negative electrode material as described in any one of claims 1 to 6.

8. An electrical device, characterized in that, Includes the secondary battery as described in claim 7.

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