Positive electrode material and preparation method therefor, and secondary battery and electric apparatus

Abstract

Provided in the present disclosure are a positive electrode material and a preparation method therefor, and a secondary battery and an electric apparatus. The positive electrode material comprises a lithium manganese oxide, wherein an X-ray diffraction analysis pattern of the lithium manganese oxide comprises a first diffraction peak with a 2θ diffraction angle between 18.2° and 18.6° and a second diffraction peak with a 2θ diffraction angle between 18.6° and 19.0°.

Description

Cathode material, preparation method thereof, secondary battery, and electric device

[0001] Cross-reference to related applications

[0002] The present disclosure is based on and claims priority to Chinese Patent Application No. 202411035277.8, filed on July 30, 2024, entitled “Cathode material, preparation method thereof, secondary battery, and electric device”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of batteries, and in particular to a cathode material, a preparation method thereof, a secondary battery, and an electric device. BACKGROUND

[0004] In recent years, with the application range of batteries becoming more and more extensive, batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, etc. Since batteries have made great progress, higher requirements have been placed on the service life of batteries. How to prolong the service life of batteries has become a research hotspot in the field of batteries. SUMMARY

[0005] The present disclosure is made in view of the above-mentioned problems, and aims to provide a cathode material, a preparation method thereof, a secondary battery, and an electric device. The secondary battery using the cathode material has improved cycle performance and storage performance, thereby having a prolonged service life.

[0006] To achieve the above-mentioned purpose, the present disclosure provides, in a first aspect, a cathode material, the cathode material comprising a lithium manganese oxide, and an X-ray diffraction analysis spectrum of the lithium manganese oxide comprising a first diffraction peak at a 2θ diffraction angle of 18.2° to 18.6° and a second diffraction peak at a 2θ diffraction angle of 18.6° to 19.0°.

[0007] The spinel lithium manganese oxide is a cubic crystal with Fd3m symmetry. In the related art, the 8a position of the tetrahedron in the cubic crystal structure is occupied by lithium ions, and the 16c position of the octahedron is all vacant. The lithium ions at the 8a position are relatively stable and are not easy to release, and the release potential needs to be at 4V vs. Li / Li + Above. In the cathode material of the present disclosure, the presence of the first diffraction peak indicates that lithium is embedded in the 16c position of the octahedron, corresponding to the lithium-embedded phase of the lithium manganese oxide, and the second diffraction peak corresponds to the non-lithium-embedded phase of the lithium manganese oxide. The lithium embedded in the 16c position is active and easy to release, and the release potential is at 3V vs. Li / Li +Approximately. Therefore, during the first charge, the over-intercalated lithium in the lithium manganese oxide is released, while Mn... 3+ Transform into Mn 4+ The released lithium can be transferred to the negative electrode and stored in the negative electrode material to compensate for the loss of active lithium during battery cycling. This helps to improve the battery's cycle performance and storage performance, thereby extending the battery's lifespan.

[0008] In some embodiments, the molar ratio M1 of lithium to manganese in lithium manganese oxide is 0.51 ≤ M1 < 1.33. By controlling M1 within the above range, it is beneficial to have an appropriate amount of lithium intercalation in the cathode material, while also helping to maintain the structural stability of the cathode material. This is beneficial to improving the cycle performance and storage performance of the battery, thereby extending the battery's lifespan.

[0009] In some embodiments, the chemical formula of lithium manganese oxide includes: Li 1+x Mn 2-y M y O 4-k-z X z Wherein, 0.02≤x<1, 0≤y≤0.5, 0≤z≤1, 0≤k≤0.5; M includes one or more of Cu, Ni, Co, Mg, Ca, Ba, Zn, Fe, Ti, Zr, W, Nb, Al, B, P, Mo, V, Cr, and Si; X includes one or more of S, F, and Cl.

[0010] In some embodiments, the ratio R of the peak intensity of the first diffraction peak to the peak intensity of the second diffraction peak is 0 < R ≤ 10. By controlling R within the above range, it is beneficial to have an appropriate amount of lithium intercalation in the cathode material, while also helping to maintain the structural stability of the cathode material.

[0011] In some implementations, 0 < R ≤ 2. By controlling R within the above range, it is beneficial to have an appropriate amount of lithium intercalation in the cathode material, while also helping to further maintain the structural stability of the cathode material.

[0012] In some embodiments, during the process of heating the cathode material from 25°C to 400°C in an oxygen-containing atmosphere, the weight gain rate of the cathode material is less than 0.7%. The weight gain rate is calculated using the following formula: (m1-m0) / m0×100%, where m0 represents the mass of the cathode material at 25°C during the heating process, and m1 represents the mass of the cathode material at 400°C during the heating process. A weight gain rate within the above range indicates that the material exhibits good stability below 400°C, which is beneficial for extending the battery's lifespan.

[0013] In some embodiments, the volume average particle size Dv50 of the cathode material is between 3 μm and 30 μm. By controlling the volume average particle size Dv50 of the cathode material within the above range, it is beneficial to ensure that the over-intercalated lithium is uniformly distributed inside and on the surface of the cathode material particles, reducing the stress and strain inside and on the surface of the cathode material; on the other hand, it ensures that the specific surface area of ​​the cathode material is moderate, reducing the side reactions between the cathode material and the electrolyte in the battery, thereby helping to reduce the internal resistance of the battery and thus extend the battery's service life.

[0014] In some implementations, the BET specific surface area of ​​the cathode material is 0.2 m². 2 / g to 5.0m 2 / g. By controlling the BET specific surface area of ​​the cathode material within the above range, it is beneficial to reduce the side reactions between the cathode material and the electrolyte in the battery, thereby reducing the internal resistance of the battery and extending its service life.

[0015] In some embodiments, the pH value of the cathode material is between 7 and 13. By controlling the pH value of the cathode material within the above range, it is beneficial to suppress gelation of the cathode slurry prepared based on the cathode material, and also to reduce the dissolution of transition metals (e.g., Mn) in the cathode material.

[0016] A second aspect of this disclosure provides a method for preparing a cathode material, the method comprising:

[0017] S1: Mix the cathode material precursor, lithium salt and optional reducing agent in a solvent to obtain a mixture;

[0018] S2: React the mixture to obtain a cathode material, wherein the cathode material includes lithium manganese oxide, and the X-ray diffraction analysis pattern of the lithium manganese oxide includes a first diffraction peak with a 2θ diffraction angle between 18.2° and 18.6° and a second diffraction peak with a 2θ diffraction angle between 18.6° and 19.0°.

[0019] The cathode material prepared by the above method includes a first diffraction peak corresponding to the lithium-intercalated phase and a second diffraction peak corresponding to the non-lithium-intercalated phase, indicating that the cathode material is a spinel lithium manganese oxide cathode material with over-lithiation. During the first charge process, the Mn in the over-lithium-intercalated lithium manganese oxide... 3+ Transform into Mn 4+ It releases over-intercalated lithium, which can be transferred to the negative electrode and stored in the negative electrode material to compensate for the loss of active lithium during battery cycling. This helps to improve the battery's cycle performance and storage performance, thereby extending the battery's lifespan.

[0020] In some embodiments, the chemical formula of the cathode material precursor includes: Li δ Mn2-y M y O 4-k-z X z Wherein, 0.9≤δ≤1, 0≤y≤0.5, 0≤z≤1, 0≤k≤0.5; M includes one or more of Cu, Ni, Co, Mg, Ca, Ba, Zn, Fe, Ti, Zr, W, Nb, Al, B, P, Mo, V, Cr, and Si; X includes one or more of F, S, and Cl.

[0021] In some embodiments, the molar ratio M2 of the cathode material precursor to the lithium salt is 0.5 ≤ M2 ≤ 15. This facilitates the insertion of an appropriate amount of lithium into the cathode material precursor, thereby obtaining a cathode material with moderate lithium insertion and stable structure.

[0022] In some embodiments, in step S2, the reaction is carried out at a temperature of 10°C to 100°C; and / or, the reaction is carried out for 0.5 h to 30 h. By selecting the above-mentioned reaction temperature and / or time, it is beneficial to obtain a cathode material with moderate lithium intercalation and stable structure.

[0023] In some embodiments, in step S1, the cathode material precursor and lithium salt are mixed in a solvent to obtain a mixture, wherein the lithium salt comprises a Li / Li salt with an oxidation potential of less than 2.9V. + The reducing lithium salt.

[0024] In some embodiments, the reducing lithium salt includes one or more of lithium sulfide, lithium iodide, lithium borohydride, or lithium hydrosulfide. In these embodiments, the reducing lithium salt can simultaneously provide lithium and reduce the cathode material precursor. Therefore, in these embodiments, no additional reducing agent needs to be added.

[0025] In some embodiments, the concentration of the reduced lithium salt in the mixture is 0.01 mol / L to 5 mol / L; and / or the mass fraction of the cathode material precursor in the mixture is 1% to 75%. Controlling the concentration of the reduced lithium salt within the above range is beneficial for obtaining a cathode material with moderate lithium intercalation and stable structure. Controlling the mass fraction of the cathode material precursor within the above range is beneficial for obtaining a cathode material with uniformly distributed lithium intercalation.

[0026] In some embodiments, in step S1, the cathode material precursor, lithium salt and reducing agent are mixed in a solvent to obtain a mixture.

[0027] In some embodiments, the lithium salt includes one or more of lithium carbonate, lithium chloride, lithium sulfate, lithium bisulfate, lithium acetate, lithium bromide, lithium nitrate, lithium phosphate, lithium sulfide, lithium iodide, lithium borohydride, or lithium hydrosulfide; and / or the reducing agent includes one or more of diethylene glycol, sodium borohydride, or sodium hydrosulfide.

[0028] In some embodiments, the concentration of the reducing agent in the mixture is 0.01 mol / L to 5 mol / L; and / or the concentration of the lithium salt in the mixture is 0.01 mol / L to 5 mol / L; and / or the mass fraction of the cathode material precursor in the mixture is 1% to 75%. Controlling the concentrations of the lithium salt and / or the reducing agent within the above ranges is beneficial for obtaining a cathode material with moderate lithium intercalation and stable structure. Controlling the mass fraction of the cathode material precursor within the above ranges is beneficial for obtaining a cathode material with a uniform distribution of lithium intercalation.

[0029] The third aspect of this disclosure provides a secondary battery, which includes a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode material of the first aspect or the positive electrode material prepared according to the method of the second aspect.

[0030] The fourth aspect of this disclosure provides an electrical device, which includes a secondary battery as described in the third aspect. Attached Figure Description

[0031] Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0032] Figure 2 is an exploded view of a battery cell according to an embodiment of the present disclosure shown in Figure 1.

[0033] Figure 3 is a schematic diagram of a battery module according to one embodiment of the present disclosure.

[0034] Figure 4 is a schematic diagram of a battery pack according to one embodiment of the present disclosure.

[0035] Figure 5 is an exploded view of a battery pack according to an embodiment of the present disclosure, as shown in Figure 4.

[0036] Figure 6 is a schematic diagram of an electrical device in which a battery is used as a power source according to an embodiment of the present disclosure.

[0037] Figure 7 shows SEM images of the cathode material prepared in Example 1 (Figure 7(2)) and the cathode material of Comparative Example 1 (Figure 7(1)).

[0038] Figure 8 shows the X-ray diffraction patterns of the cathode material (LLMO) prepared in Example 1 and the cathode material (LMO) in Comparative Example 1.

[0039] Figure 9 shows the thermogravimetric analysis curves of the cathode material (LLMO) prepared in Example 1 and the cathode material (LMO) in Comparative Example 1.

[0040] Figure 10 shows the dQ / dV curves of the cathode material (LLMO) prepared in Example 1 and the cathode material (LMO) in Comparative Example 1.

[0041] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0042] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode material, its preparation method, secondary battery, and power application device of this disclosure. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this disclosure and are not intended to limit the subject matter of the claims.

[0043] The "range" disclosed in this disclosure is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is expected that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this disclosure, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0044] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0045] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0046] Unless otherwise specified, all steps in this disclosure may be performed sequentially or randomly, preferably sequentially. For example, if a method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if it is mentioned that the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0047] Unless otherwise specified, the terminology used in this disclosure has the common meaning as commonly understood by those skilled in the art.

[0048] Unless otherwise specified, the values ​​of the parameters mentioned in this disclosure can be determined using various test methods commonly used in the art. For example, they can be determined according to the test methods given in this disclosure.

[0049] Unless otherwise specified, in this disclosure, the term "active ion" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of a battery, including but not limited to lithium ions.

[0050] Spinel lithium manganese oxide cathode material is widely used as a cathode material in batteries due to its low cost, high initial efficiency, and good safety and reliability.

[0051] However, spinel lithium manganese oxide cathode materials suffer from manganese leaching during battery charging and discharging due to factors such as Jahn-Teller distortion. The leached Mn... 2+ Deposition onto the negative electrode damages the solid electrolyte interphase (SEI) film. Therefore, a large amount of active lithium is required to repair the SEI film, leading to rapid capacity decay, poor storage performance, and short battery life.

[0052] How to replenish active lithium to improve the cycle performance and storage performance of batteries, and thus extend their service life, has become an urgent problem to be solved in this field.

[0053] Based on this, this disclosure proposes a positive electrode material and its preparation method, a secondary battery, and an electrical device. The invention and its optional embodiments are described in more detail below.

[0054] cathode materials

[0055] The first aspect of this disclosure provides a cathode material comprising lithium manganese oxide, wherein the X-ray diffraction pattern of the lithium manganese oxide includes a first diffraction peak between 18.2° and 18.6° and a second diffraction peak with a 2θ diffraction angle between 18.6° and 19.0°.

[0056] Spinel lithium manganese oxide is a cubic crystal with Fd3m symmetry. In related technologies, the 8a positions of the tetrahedra in this cubic crystal structure are occupied by lithium ions, while the 16c positions of the octahedrons are all vacant. The lithium ions at the 8a positions are relatively stable and not easily released; the release potential requires 4V vs. Li / Li. + above.

[0057] In the cathode material of this disclosure, the presence of a first diffraction peak with a 2θ diffraction angle between 18.2° and 18.6° indicates lithium intercalation at the 16c position of the octahedron, corresponding to the characteristic peak of the lithium-intercalated phase in lithium manganese oxide. A second diffraction peak with a 2θ diffraction angle between 18.6° and 19.0° corresponds to the characteristic peak of the non-lithium-intercalated phase in lithium manganese oxide. The inclusion of these first and second diffraction peaks in the cathode material of this disclosure indicates that the cathode material is an over-intercalated spinel lithium manganese oxide cathode material. When this over-intercalated spinel lithium manganese oxide cathode material is assembled in a battery, its discharge voltage can be cut off at the characteristic 2.9V reaction potential (Mn) of the over-intercalated spinel lithium manganese oxide cathode material. 3+ / Mn 4+ Redox potential vs. Li / Li + The above. During the first charge, Mn in the over-intercalated lithium manganese oxide... 3+ Transform into Mn 4+ The over-intercalated lithium is released and can be transferred to the negative electrode and stored in the negative electrode material to compensate for the loss of active lithium during battery cycling. This improves the battery's cycle performance and storage performance, thereby extending the battery's lifespan. After the first charge and discharge, the positive electrode material transforms into a spinel lithium manganese oxide positive electrode material that has not undergone over-intercalation of lithium. Therefore, while maintaining the structural stability of the positive electrode material, it can replenish a large amount of active lithium in the battery.

[0058] In related technologies, lithium replenishment through additives mainly falls into two categories: positive electrode lithium replenishment and negative electrode lithium replenishment. Positive electrode lithium replenishment primarily utilizes lithium-rich materials, such as lithium-rich compounds like Li₂NiO₂ and Li₆CoO₄. However, these materials have relatively low specific capacity. Another type of lithium salt, such as Li₂C₄O₄, while having a higher specific capacity, decomposes and produces gas during the initial charging process. Negative electrode lithium replenishment is mainly divided into chemical lithiation and electrochemical lithiation. Chemical lithiation uses lithium metal sheets, lithium metal powder, or lithium-containing compounds such as Li-Si alloys and Li₂... 2.6 Co 0.4 Lithium compensation is achieved using N and other methods. Although these methods have good lithium compensation effects, these lithium-compensating materials are highly reactive and incompatible with existing negative electrode fabrication processes.

[0059] When the cathode material of this disclosure is applied to a battery, the battery's discharge potential is cut off above 2.9V. During the first charge, the lithium over-intercalated in the cathode material can be stored in the anode to compensate for the loss of active lithium during battery cycling. This improves the battery's capacity retention during cycling, enhances cycle performance and storage performance, thereby extending battery life, and eliminates problems such as gas generation.

[0060] In this disclosure, X-ray diffraction patterns can be determined using instruments and methods known in the art. For example, X-ray powder diffractometers can be used according to JIS K 0131-1996. For instance, a Bruker D8 ADVANCE X-ray diffractometer with a Cu target can be used.

[0061] In some embodiments, the molar ratio M1 of lithium to manganese in lithium manganese oxide is 0.51 ≤ M1 < 1.33. For example, the molar ratio M1 of lithium to manganese in lithium manganese oxide can be 0.51, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, or a value within a range of any two of these values. By controlling M1 within the above range, it is beneficial to have an appropriate amount of lithium intercalation in the cathode material, while also helping to maintain the structural stability of the cathode material, thereby improving the cycle performance and storage performance of the battery, and thus extending the battery's lifespan.

[0062] In some embodiments, the chemical formula of lithium manganese oxide includes: Li 1+x Mn 2-y M y O 4-k-z X zWherein, 0.02≤x<1, 0≤y≤0.5, 0≤z≤1, 0≤k≤0.5; M includes one or more of Cu, Ni, Co, Mg, Ca, Ba, Zn, Fe, Ti, Zr, W, Nb, Al, B, P, Mo, V, Cr, and Si; X includes one or more of S, F, and Cl. For example, x can be a value between 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.13, 0.15, 0.19, 0.2, 0.3, 0.34, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or any two of these values. For example, y can be a value between 0, 0.1, 0.2, 0.3, 0.4, 0.5, or any two of these values. For example, z can be a value between 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or any two of these values. For example, k can be a value between 0, 0.1, 0.2, 0.3, 0.4, 0.5, or any two of these values.

[0063] In some embodiments, the cathode material includes spinel lithium manganese oxide.

[0064] In some embodiments, the chemical formula of lithium manganese oxide includes: Li 1+x Mn 2-y M y O4, where x, y, and M are as defined above.

[0065] In some embodiments, the chemical formula of lithium manganese oxide includes: Li 1+x Mn2O4, where 0.02 ≤ x < 1.

[0066] In some embodiments, the first diffraction peak with a 2θ diffraction angle between 18.2° and 18.6° corresponds to the characteristic peak of the lithium-intercalated phase Li2Mn2O4, and the second diffraction peak with a 2θ diffraction angle between 18.6° and 19.0° corresponds to the characteristic peak of the non-lithium-intercalated phase LiMn2O4.

[0067] In some embodiments, the ratio of the peak intensity of the first diffraction peak to the peak intensity of the second diffraction peak is expressed as R, where 0 < R ≤ 10. Optionally, 0 < R ≤ 2. Further optionally, 0 < R ≤ 1. Still further optionally, 0.2 ≤ R ≤ 0.87. For example, R can be a value between 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any combination of these values. R represents the ratio of the peak intensities of the diffraction peaks of the lithium-intercalated phase and the non-lithium-intercalated phase in the spinel lithium manganese oxide cathode material. A larger R value indicates a higher lithium intercalation content in the cathode material of this disclosure. By controlling R within the above range, it is beneficial to have an appropriate amount of lithium intercalation in the cathode material, while also helping to maintain the structural stability of the cathode material.

[0068] In some embodiments, during the process of heating the cathode material from 25°C to 400°C in an oxygen-containing atmosphere, the weight gain rate of the cathode material is less than 0.7%, optionally ≤0.67%. The weight gain rate is calculated using the following formula: (m1-m0) / m0×100%, where m0 represents the mass of the cathode material at 25°C during the heating process; and m1 represents the mass of the cathode material at 400°C during the heating process. The oxygen-containing atmosphere includes, but is not limited to, an air atmosphere.

[0069] For example, the weight gain rate can be a value between 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.67%, or any combination of these values. The low weight gain rate of the cathode material disclosed in this invention indicates that the material has good stability below 400°C, which is beneficial for extending the battery's lifespan.

[0070] In some embodiments, the volume average particle size Dv50 of the cathode material is from 3 μm to 30 μm, optionally from 3 μm to 13 μm. For example, the volume average particle size Dv50 of the cathode material can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 15 μm, 20 μm, 30 μm, or a value within a range of any two of these values. By controlling the volume average particle size Dv50 of the cathode material within the above range, it is beneficial to ensure that the over-intercalated lithium is uniformly distributed inside and on the surface of the cathode material particles, reducing the stress and strain inside and on the surface of the cathode material; on the other hand, it ensures that the specific surface area of ​​the cathode material is moderate, reducing the side reactions between the cathode material and the electrolyte in the battery, thereby helping to reduce the internal resistance of the battery and thus extending the battery's service life.

[0071] In some implementations, the BET specific surface area of ​​the cathode material is 0.2 m². 2 / g to 5.0m 2 / g, optionally 0.4m 2 / g to 5.0m 2 / g, optionally 0.4m 2 / g to 1.5m 2 / g. For example, the BET specific surface area of ​​the cathode material can be 0.2m². 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g、1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g、5m 2 / g or a value within a range of any two of these values. By controlling the BET specific surface area of ​​the cathode material within the above range, it is beneficial to reduce side reactions between the cathode material and the electrolyte in the battery, thereby reducing the battery's internal resistance and extending its lifespan.

[0072] In some embodiments, the pH value of the cathode material is 7 to 13, optionally 10 to 13. For example, the pH value of the cathode material can be a value between 7, 8, 9, 10, 11, 12, 13, or any combination of these values. By controlling the pH value of the cathode material within the above range, it is beneficial to suppress gelation in the cathode slurry prepared based on the cathode material, and also to reduce the dissolution of transition metals (e.g., Mn) in the cathode material.

[0073] Preparation method of positive electrode material

[0074] The second aspect of this disclosure provides a method for preparing a cathode material. The preparation method includes:

[0075] S1: Mix the cathode material precursor, lithium salt and optional reducing agent in a solvent to obtain a mixture;

[0076] S2: React the mixture to obtain a cathode material, wherein the cathode material includes lithium manganese oxide, and the X-ray diffraction analysis pattern of the lithium manganese oxide includes a first diffraction peak with a 2θ diffraction angle between 18.2° and 18.6° and a second diffraction peak with a 2θ diffraction angle between 18.6° and 19.0°.

[0077] The term "cathode material precursor" refers to the precursor material used to prepare the cathode material of this disclosure. This precursor material itself can also be used as a cathode active material. The precursor material is reduced in the presence of a lithium salt and an optional reducing agent to form a lithium-intercalated cathode material. The X-ray diffraction pattern of this lithium-intercalated cathode material using a Cu target includes a first diffraction peak with a 2θ diffraction angle between 18.2° and 18.6° and a second diffraction peak with a 2θ diffraction angle between 18.6° and 19.0°.

[0078] The first diffraction peak with a 2θ diffraction angle between 18.2° and 18.6° corresponds to the characteristic peak of the lithium-intercalated phase in lithium manganese oxide. The second diffraction peak with a 2θ diffraction angle between 18.6° and 19.0° corresponds to the characteristic peak of the non-lithium-intercalated phase in lithium manganese oxide. The presence of these first and second diffraction peaks in the cathode material prepared by the above method indicates that the cathode material is an over-lithium-intercalated spinel lithium manganese oxide cathode material. When this over-lithium-intercalated spinel lithium manganese oxide cathode material is assembled in a battery, its discharge voltage can be cut off at the characteristic 2.9V reaction potential (Mn) of the over-lithium-intercalated spinel lithium manganese oxide cathode material. 3+ / Mn 4+ Redox potential vs. Li / Li + The above. During the first charge, Mn in the over-intercalated lithium manganese oxide... 3+ Transform into Mn 4+ The over-intercalated lithium is released and can be transferred to the negative electrode and stored in the negative electrode material to compensate for the loss of active lithium during battery cycling. This improves the battery's cycle performance and storage performance, thereby extending the battery's lifespan. After the first charge and discharge, the positive electrode material transforms into a spinel lithium manganese oxide positive electrode material that has not undergone over-intercalation of lithium. Therefore, while maintaining the structural stability of the positive electrode material, it can replenish a large amount of active lithium in the battery.

[0079] The phrase "optional reducing agent" means that a reducing agent may or may not be added in step S1. When the lithium salt in step S1 is a reducing lithium salt, a reducing agent may or may not be added. When the lithium salt in step S1 is not a reducing lithium salt, a reducing agent needs to be added. In this document, a reducing lithium salt refers to an oxidation potential less than 2.9V vs. Li / Li + Lithium salts.

[0080] In some embodiments, the chemical formula of the cathode material precursor includes: Li δ Mn 2-y M y O 4-k-z X z Wherein, 0.9≤δ≤1, 0≤y≤0.5, 0≤z≤1, 0≤k≤0.5; M includes one or more of Cu, Ni, Co, Mg, Ca, Ba, Zn, Fe, Ti, Zr, W, Nb, Al, B, P, Mo, V, Cr, and Si; X includes one or more of F, S, and Cl. For example, δ can be a value between 0.9, 0.95, 1, or any two of these values. For example, y can be a value between 0, 0.1, 0.2, 0.3, 0.4, 0.5, or any two of these values. For example, z can be a value between 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or any two of these values. For example, k can be a value between 0, 0.1, 0.2, 0.3, 0.4, 0.5, or any two of these values. Optionally, the chemical formula of the cathode material precursor includes Li δ Mn 2-y M y O4, where δ, y, and M are as defined above. Optionally, the chemical formula of the cathode material precursor includes LiMn2O4.

[0081] In some embodiments, the molar ratio M2 of the cathode material precursor to the lithium salt is 0.5 ≤ M2 ≤ 15, optionally 1.0 ≤ M2 ≤ 5.0, optionally 1.4 ≤ M2 ≤ 4.5, optionally 1.4 ≤ M2 ≤ 3.0, and optionally 1.4 ≤ M2 ≤ 2.2. For example, the molar ratio M2 of the cathode material precursor to the lithium salt can be 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a value within a range of any two of these values. This facilitates the insertion of an appropriate amount of lithium into the cathode material precursor to obtain a cathode material with moderate lithium insertion and stable structure.

[0082] In some embodiments, the reaction in step S2 is carried out at a temperature between 10°C and 100°C. For example, the reaction temperature can be a value between 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, or any combination of these values. At the above reaction temperatures, the reaction rate is moderate, which is beneficial for obtaining a cathode material with moderate lithium intercalation and stable structure.

[0083] In some embodiments, in step S2, the reaction proceeds for 0.5 h to 30 h, optionally 3 h to 24 h. For example, the reaction time can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, 24 h, 25 h, 26 h, 27 h, 28 h, 29 h, 30 h, or a range of any two of these values. By selecting the above reaction time, it is beneficial to obtain a cathode material with moderate lithium intercalation and stable structure.

[0084] In some embodiments, in step S1, the cathode material precursor and lithium salt are mixed in a solvent to obtain a mixture, wherein the lithium salt comprises an oxidation potential of less than 2.9V vs. Li / Li + The reduced lithium salt is used. In these embodiments, the concentration of the reduced lithium salt in the mixture can be 0.01 mol / L to 5 mol / L, optionally 0.5 mol / L to 4 mol / L, or optionally 1 mol / L to 3 mol / L. For example, the concentration of the reduced lithium salt in the mixture can be 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, or a value within a range of any two of these values. By controlling the concentration of the reduced lithium salt within the above range, it is beneficial to obtain a cathode material with moderate lithium intercalation and stable structure. In these embodiments, the mass fraction of the cathode material precursor in the mixture can be 1% to 75%, optionally 30% to 60%, optionally 35% to 50%, or optionally 40% to 50%. For example, the mass fraction of the cathode material precursor in the mixture can be 1%, 10%, 15%, 20%, 30%, 37%, 40%, 43%, 46%, 50%, 60%, 70%, 75%, or any combination of these values. By controlling the mass fraction of the cathode material precursor within the above range, it is beneficial to obtain a cathode material with a uniform distribution of lithium intercalation.

[0085] This disclosure does not specifically limit the type of reducing lithium salt; any salt with an oxidation potential of less than 2.9V vs. Li / Li can be used, as is known in the art. +The lithium salt is used. In some embodiments, the reducing lithium salt includes one or more of lithium sulfide, lithium iodide, lithium borohydride, or lithium hydrosulfide. Optionally, the reducing lithium salt includes lithium iodide. Optionally, the reducing lithium salt is lithium iodide. In embodiments using a reducing lithium salt, the reducing lithium salt can simultaneously serve as both a source of lithium and a precursor for reducing the cathode material. Therefore, in these embodiments, no additional reducing agent needs to be added.

[0086] In some embodiments, in step S1, the cathode material precursor, lithium salt, and reducing agent are mixed in a solvent to obtain a mixture. In these embodiments, since a reducing agent is added in step S1, the lithium salt can be a reducing or non-reducing lithium salt. In these embodiments, the concentration of the reducing agent in the mixture can be 0.01 mol / L to 5 mol / L, optionally 0.5 mol / L to 4 mol / L, or optionally 1 mol / L to 3 mol / L. Controlling the concentration of the reducing agent within the above range is beneficial for obtaining a cathode material with moderate lithium intercalation and stable structure. In these embodiments, the concentration of the lithium salt in the mixture can be 0.01 mol / L to 5 mol / L, optionally 0.5 mol / L to 4 mol / L, or optionally 1 mol / L to 3 mol / L. Controlling the concentration of the lithium salt within the above range is beneficial for obtaining a cathode material with moderate lithium intercalation and stable structure. In these embodiments, the mass fraction of the cathode material precursor in the mixture can be 1% to 75%, optionally 30% to 60%, or optionally 35% to 50%. By controlling the mass fraction of the cathode material precursor within the above range, it is beneficial to obtain a cathode material with a uniform distribution of lithium intercalation.

[0087] This disclosure does not specifically limit the type of lithium salt; any lithium salt known in the art that can provide lithium can be used. In some embodiments, the lithium salt may include one or more of lithium carbonate, lithium chloride, lithium sulfate, lithium bisulfate, lithium acetate, lithium bromide, lithium nitrate, lithium phosphate, lithium sulfide, lithium iodide, lithium borohydride, or lithium hydrosulfide. Optionally, the lithium salt may include lithium carbonate. Optionally, the lithium salt may be lithium carbonate.

[0088] In some embodiments, the oxidation potential of the reducing agent is less than 2.9V vs Li / Li + For example, the reducing agent may include one or more of diethylene glycol, sodium borohydride, or sodium hydrosulfide.

[0089] In some embodiments, the solvent may include one or more of H2O, ethylene glycol dimethyl ether, acetonitrile, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, and fluoroethylene carbonate.

[0090] Secondary batteries

[0091] The third aspect of this disclosure provides a secondary battery.

[0092] The term "secondary battery" used in this article refers to a single battery cell, a battery module, or a battery pack. These will be explained separately below.

[0093] Typically, a single secondary battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0094] Positive electrode sheet

[0095] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes the positive electrode material of the first aspect of this disclosure or the positive electrode material prepared according to the method of the second aspect of this disclosure.

[0096] In some embodiments, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0097] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0098] In some embodiments, the positive electrode material in the positive electrode sheet may further include positive electrode active materials known in the art for lithium batteries. As an example, these positive electrode active materials may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), layered lithium manganese oxides (such as LiMnO2), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNiO2). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM)333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.1 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0099] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in different molar contents of Li at different discharge states. In the description of the positive electrode active material in this disclosure, the molar contents of Li refer to the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar contents of Li will change after charge-discharge cycles.

[0100] In the description of the positive electrode active material in this disclosure, the molar content of O is only a theoretical value. The release of oxygen from the crystal lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0101] In this disclosure, the terms "cathode material" and "cathode active material" are used interchangeably.

[0102] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0103] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0104] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0105] Negative electrode sheet

[0106] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0107] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0108] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0109] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide compounds, and tin alloys. However, this disclosure is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0110] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0111] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0112] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0113] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0114] electrolytes

[0115] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This disclosure does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0116] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0117] In some embodiments, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0118] In some embodiments, the solvent of the electrolyte may include at least one selected from ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0119] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0120] Separating membrane

[0121] In some embodiments, the battery cell also includes a separator. This disclosure does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0122] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0123] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0124] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0125] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0126] This disclosure does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0127] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0128] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0129] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0130] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0131] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0132] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0133] Electrical appliances

[0134] This disclosure provides a fourth aspect of an electrical device, which includes the secondary battery provided in the third aspect of this disclosure. The secondary battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0135] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0136] Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this device, a battery pack or battery module can be used.

[0137] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0138] Example

[0139] The embodiments of this disclosure are illustrated below. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0140] I. Preparation of cathode materials

[0141] Example 1

[0142] S11: Add 102g of reducing lithium salt LiI to 200g of acetonitrile solvent and stir until homogeneous. The concentration of LiI is 3mol / L.

[0143] S12: Add 200g of positive electrode material precursor LiMn2O4 (purchased from Maclean) to the solution obtained in S11 above, stir evenly to obtain a mixture.

[0144] S2: The mixture obtained in S12 is reacted at 80°C for 24 hours. Then, the reacted mixture is filtered, and the filter cake is washed with ethanol. The filter cake is then vacuum dried at 100°C for 24 hours to obtain the positive electrode material of Example 1.

[0145] Example 2

[0146] The cathode material was prepared according to the preparation method of Example 1, with the only difference being:

[0147] The mixture obtained in S12 is reacted at a temperature of 25°C.

[0148] Example 3

[0149] The cathode material was prepared according to the preparation method of Example 1, with the only difference being:

[0150] The mixture obtained in S12 is reacted at a temperature of 60°C.

[0151] Example 4

[0152] The cathode material was prepared according to the preparation method of Example 1, with the only difference being:

[0153] The mixture obtained in S12 is reacted at a temperature of 100°C.

[0154] Example 5

[0155] The cathode material was prepared according to the preparation method of Example 1, with the only difference being:

[0156] The mixture obtained in S12 was allowed to react for 3 hours.

[0157] Example 6

[0158] The cathode material was prepared according to the preparation method of Example 1, with the only difference being:

[0159] The mixture obtained in S12 was allowed to react for 6 hours.

[0160] Example 7

[0161] The cathode material was prepared according to the preparation method of Example 1, with the only difference being:

[0162] The mixture obtained in S12 was allowed to react for 10 hours.

[0163] Example 8

[0164] The cathode material was prepared according to the preparation method of Example 1, with the only difference being:

[0165] In S11, 34g of reducing agent LiI is added to the solvent, thus the concentration of LiI is 1mol / L.

[0166] Example 9

[0167] The cathode material was prepared according to the preparation method of Example 1, with the only difference being:

[0168] In S11, 68g of reducing agent LiI is added to the solvent, thus the concentration of LiI is 2mol / L.

[0169] Comparative Example 1

[0170] Spinel cathode material LiMn2O4 (purchased from Maclean) was used as the cathode material.

[0171] II. Cathode Material Performance Testing

[0172] 1. SEM Image Testing

[0173] The morphology of the cathode material prepared in Example 1 and the cathode material in Comparative Example 1 was observed using an emission scanning electron microscope (Karl Zeiss SIGMA-500). The cathode material in Comparative Example 1 was a precursor for the cathode material prepared in Example 1. SEM images were acquired at 1000x magnification, and the acquired SEM images are shown in Figure 7.

[0174] Figure 7(1) shows the SEM image of the cathode material of Comparative Example 1. It can be seen that the morphology of the cathode material of Comparative Example 1 is a secondary spherical particle formed by primary particles.

[0175] Figure 7(2) shows the SEM image of the cathode material of Example 1. It can be seen that the morphology of the cathode material prepared in Example 1 consists of primary particles and secondary particles formed from the primary particles.

[0176] 2. Inductively Coupled Plasma (ICP) Emission Spectroscopy Test

[0177] 0.4 g of the cathode material from Examples 1 to 9 and Comparative Example 1 were weighed and placed in beakers, and plate digestion was performed at ~200°C using a 1+1 aqua regia digestion reagent. The Li and Mn content in the cathode material was then tested using an inductively coupled plasma atomic emission spectrometer (Avio2000, PerkinElmer PE, USA). The ICP test was performed according to the "General Rules for Inductively Coupled Plasma Atomic Emission Spectroscopy". This yielded the molar ratio of Li to Mn in the cathode materials prepared in Examples 1 to 9. Furthermore, based on the difference between the initial mass of the test sample and the measured total mass of Li and Mn, the O content in the sample could be determined, thus deriving the structural formula of the cathode material.

[0178] 3. X-ray diffraction (XRD) analysis.

[0179] X-ray powder diffractometer (Bruker D8 ADVANCE) was used to test the cathode materials of Examples 1 to 9 and Comparative Example 1. The target material was Cu, the voltage and current were 40 kV / 40 mA, the scanning angle range was 15° to 70°, the scanning step size was 0.016891°, and the step time was 46.08 s. The X-ray diffraction patterns of each example and comparative example were obtained, and the R value, I(18.4°) / I(18.8°), was calculated using Jade software based on the X-ray diffraction patterns. The calculation results are shown in Table 2, where I(18.4°) represents the peak intensity of the first diffraction peak (2θ diffraction angle between 18.2° and 18.6°) in the XRD pattern, and I(18.8°) represents the peak intensity of the second diffraction peak (2θ diffraction angle between 18.6° and 19.0°) in the XRD pattern.

[0180] Referring to Figure 8, Figure 8 shows the X-ray diffraction patterns of the cathode material (LLMO) of Example 1 and the cathode material (LMO) of Comparative Example 1.

[0181] As shown in Figure 8, the X-ray diffraction pattern of the cathode material in Comparative Example 1 shows a second diffraction peak, but the first diffraction peak is absent. This second diffraction peak is a characteristic peak corresponding to the unintercalated lithium phase LiMn2O4. The X-ray diffraction pattern of the cathode material prepared in Example 1 shows both a first and a second diffraction peak. The first diffraction peak is a characteristic peak corresponding to the lithium-intercalated Li2Mn2O4 phase. The second diffraction peak is a characteristic peak corresponding to the unintercalated lithium phase LiMn2O4. The peak intensity I (18.4°) of the first diffraction peak is 5717, and the peak intensity I (18.8°) of the second diffraction peak is 7058. The ratio R of the peak intensity I (18.4°) of the first diffraction peak to that of the second diffraction peak is 0.81. This indicates that the cathode material in Example 1 is over-intercalated with lithium.

[0182] 4. Thermogravimetric analysis (TG) test

[0183] 10 mg of the cathode material from Examples 1 to 9 and Comparative Example 1 were weighed and placed in a thermogravimetric analyzer (NETZSCH STA449F3). The test atmosphere was set to air, the test temperature ranged from 25°C to 400°C, and the heating rate was 5°C / min. TG curves were obtained. Based on the TG curves, the weight gain rate of the cathode material from Examples 1 to 9 and Comparative Example 1 during the heating process from 25°C to 400°C was recorded. The weight gain rate results are shown in Table 2.

[0184] Referring to Figure 9, which shows the TG curves of the cathode material (LLMO) of Example 1 and the cathode material (LMO) of Comparative Example 1, it can be seen that the weight changes of the cathode materials of Example 1 and Comparative Example 1 are minimal within the temperature range of 25°C to 200°C. Within the temperature range of 200°C to 400°C, the weight change of the cathode material (LLMO) of Example 1 remains minimal, with almost no significant weight increase; however, the weight of the cathode material (LMO) of Comparative Example 1 continuously increases. This indicates that the cathode material (LLMO) of Example 1 exhibits good stability at temperatures below 400°C, with no other reactions occurring.

[0185] 5. Test of BET specific surface area

[0186] The BET specific surface area of ​​the cathode materials in Examples 1 to 9 and Comparative Example 1 was tested using a specific surface area analyzer (Tristar II 3020M) via nitrogen adsorption / desorption. The cathode material samples were dried in a vacuum drying oven and then placed in sample tubes for measurement in the analyzer. Specific testing was conducted according to the national standard GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method," and the results are shown in Table 2.

[0187] 6. Test of volume average particle size (Dv50)

[0188] The particle size distribution of the cathode materials in Examples 1 to 9 and Comparative Example 1 was tested using a Malvern particle size analyzer. The specific tests were conducted according to the national standard GB / T19077-2016 "Particle Size Distribution - Laser Diffraction Method". The test results are shown in Table 2.

[0189] 7. pH value test

[0190] Weigh 5g of the positive electrode material from Examples 1 to 9 and Comparative Example 1 respectively, and place them in 100mL Erlenmeyer flasks. Add 45g of CO2-free water to the Erlenmeyer flasks at a ratio of positive electrode material to solvent of 1:9. Place a magnetic rotor in the flasks and seal them with sealing film. Stir the prepared solution magnetically for 30 minutes. After stirring, let it stand for 1.5 hours. Immerse the glass bulb of a pH meter (Leici, model PHS-3C) in the solution and stabilize the reading for more than 30 seconds. The test results are shown in Table 2.

[0191] Table 1: Reaction parameters in Examples 1 to 9

[0192] Table 2: Li / Mn molar ratio and performance test results in the cathode materials of Examples 1 to 9 and Comparative Example 1

[0193] In Table 2, " / " indicates that there are no related items.

[0194] III. Battery Preparation

[0195] 1. Preparation of secondary batteries

[0196] (1) Preparation of positive electrode sheet

[0197] The positive electrode materials, conductive agent (Super P), and binder polyvinylidene fluoride (PVDF) of Examples 1 to 9 and Comparative Example 1 were added to N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1 and stirred until homogeneous to prepare a positive electrode slurry. The solid content of the positive electrode slurry was 50 wt%. The positive electrode slurry was coated onto an aluminum foil current collector, dried at 85°C, cold-pressed, and then slit to prepare a positive electrode sheet.

[0198] (2) Preparation of negative electrode sheet

[0199] A negative electrode slurry was prepared by adding the negative electrode active material (artificial graphite), conductive agent (conductive carbon black), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) to deionized water in a mass ratio of 95:1:2:2 and stirring until homogeneous. The solid content of the negative electrode slurry was 50 wt%. The negative electrode slurry was then coated onto Cu foil, dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0200] (3) Separating membrane

[0201] Polyethylene (PE) film is used as the separation membrane.

[0202] (4) Preparation of electrolyte

[0203] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC) were mixed in a mass ratio of 30:50:20. Lithium bis(fluorosulfonyl)imide (LiFSI) was then dissolved in the organic solvent to prepare the electrolyte. The concentration of LiFSI was 1 mol / L.

[0204] (5) Battery manufacturing

[0205] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. These are then wound to obtain a bare battery cell. The bare battery cell is placed in an outer package, injected with prepared electrolyte, and undergoes processes such as encapsulation, formation, and venting to obtain a lithium-ion battery.

[0206] 2. Preparation of button cells

[0207] Using the prepared positive electrode as the positive electrode and a lithium sheet as the negative electrode, a coin cell was assembled. The electrolyte used was a ethylene carbonate (EC) and ethyl methyl carbonate (EMC) solution with a volume ratio of 3:7. LiPF6 and LiBOB (lithium dioxoborate) were added as lithium salts, and vinylene carbonate was added as an additive. The concentration of LiPF6 was 1 mol / L, the mass concentration of LiBOB was 1%, and the mass concentration of vinylene carbonate was 1%.

[0208] IV. Battery Performance Testing

[0209] 1. Initial charge capacity test of button cell batteries

[0210] The prepared coin cells were kept at 25°C for 180 min, then charged to 4.3V using a constant current of 0.1C, followed by a constant voltage charge to 0.05C from 4.3V. The charging capacity at this point was recorded as Q1. The ratio of Q1 to the mass of the cathode material was then recorded as the initial charge specific capacity. The test results are shown in Table 3. The initial charge specific capacity is used to characterize the actual lithium intercalation amount of the cathode material. A larger initial charge specific capacity indicates a larger actual lithium intercalation amount of the cathode material.

[0211] 2. Testing of dQ / dV curves

[0212] The prepared coin cells were kept at 25°C for 180 minutes, then charged to 4.3V using a constant current of 0.1C, followed by a constant voltage charge to 0.05C from 4.3V. The charging capacity at this point was recorded as Q1. The ratio of Q1 to the mass of the cathode material was then recorded as the initial charge specific capacity. The dQ / dV curve was obtained by differentiating the initial charge specific capacity and voltage curves.

[0213] 3. Secondary battery cycle performance test

[0214] At 45°C, a lithium-ion battery is charged at a constant current of 1C to 4.3V, then charged at a constant voltage of 4.3V until the current is less than 0.05C. The battery is then discharged at a constant current of 1C to 3V. The discharge capacity of the first cycle is denoted as C0. This constitutes one charge-discharge cycle. This charging and discharging process is repeated until the 500th cycle, yielding the discharge capacity after 500 cycles, denoted as C. 500 The capacity retention rate of a lithium-ion battery after 500 cycles can be calculated using the following formula.

[0215] Capacity retention rate (%) of a lithium-ion battery after 500 cycles at 45℃ = (Discharge capacity C of the 500th cycle) 500 / Discharge capacity of the first cycle (C0) × 100%.

[0216] 4. Secondary battery storage performance test

[0217] At 25°C, the lithium-ion battery was charged at a constant current of 1C to 4.3V, then charged at a constant voltage of 4.3V until the current was less than 0.05C, and then discharged at 0.33C to 3V to obtain the discharge capacity Q. Next, it was charged at a constant current of 1C to 4.3V, and then charged at a constant voltage of 4.3V until the current was less than 0.05C. Finally, the battery was placed in a 45°C oven for 200 days.

[0218] After the battery was stored for 200 days, it was removed and placed at 25°C for 12 hours. Then, the battery was charged at a constant current of 1C to 4.3V, followed by constant voltage charging at 4.3V until the current was less than 0.05C. Finally, it was discharged at 0.33C to 3V to obtain the discharge capacity Q. 200Capacity retention after 200 days of storage at 45°C and 4.3V = Q / Q 200 ×100%.

[0219] Table 3: Battery Performance Test Results

[0220] As can be seen from the data in Tables 2 and 3, compared with the battery of Comparative Example 1, the X-ray diffraction analysis pattern of the positive electrode material used in the positive electrode sheet of the batteries of Examples 1 to 9 contains the first diffraction peak and the second diffraction peak. The batteries of Examples 1 to 9 have higher initial charge specific capacity, and the batteries of Examples 1 to 9 have better cycle performance and storage performance, thereby having an extended service life.

[0221] Referring to Figure 10, which shows the dQ / dV curves of the cathode material (LMO) of Comparative Example 1 and the cathode material (LLMO) prepared in Example 1, where dQ / dV is the result of the capacity of the coin cell differentiated from the voltage. As can be seen from Figure 10, the dQ / dV curve of the cathode material LMO (LiMn2O4) only includes one set of oxidation peaks in the range of 3.9V to 4.25V; while the cathode material LLMO also includes the following two sets of oxidation peaks: the first set of peaks is in the range of 2.9V to 3.2V, and the second set of peaks is in the range of 3.7V to 3.9V. These two sets of peaks correspond to the delithiation oxidation peaks of lithium intercalated at the 16c position. This further illustrates that the cathode material LLMO of Example 1 is over-intercalated with lithium.

[0222] Based on the "specific capacity at first charge" data in Table 3, it can be inferred that the active lithium content of LLMO is greater than that of LMO. After the first charge, the lithium ions over-intercalated in LLMO can be stored in the negative electrode, replenishing the active lithium ions lost during battery cycling, thereby improving the battery's cycle performance and storage performance, and thus extending the battery's lifespan.

[0223] It should be noted that this disclosure is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same essential structure and achieving the same effect as the technical concept within the scope of this disclosure are included in the technical scope of this disclosure. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included in the scope of this disclosure without departing from the spirit of this disclosure.

Claims

1. A cathode material comprising lithium manganese oxide, wherein the X-ray diffraction pattern of the lithium manganese oxide comprises a first diffraction peak with a 2θ diffraction angle between 18.2° and 18.6° and a second diffraction peak with a 2θ diffraction angle between 18.6° and 19.0°.

2. The cathode material according to claim 1, wherein, The molar ratio M1 of lithium to manganese in the lithium manganese oxide is 0.51 ≤ M1 < 1.

33.

3. The cathode material according to claim 1 or 2, wherein, The chemical formula of the lithium manganese oxide includes: Li 1+x Mn 2-y M y O 4-k-z X z Wherein, 0.02≤x<1, 0≤y≤0.5, 0≤z≤1, 0≤k≤0.5; M includes one or more of Cu, Ni, Co, Mg, Ca, Ba, Zn, Fe, Ti, Zr, W, Nb, Al, B, P, Mo, V, Cr, and Si; X includes one or more of S, F, and Cl.

4. The cathode material according to any one of claims 1 to 3, wherein, The ratio R of the peak intensity of the first diffraction peak to the peak intensity of the second diffraction peak is 0 < R ≤ 10.

5. The cathode material according to claim 4, wherein, 0＜R≤2。 6. The cathode material according to any one of claims 1 to 5, wherein, During the process of heating the positive electrode material from 25°C to 400°C in an oxygen-containing atmosphere, the weight gain rate of the positive electrode material is less than 0.7%; the weight gain rate is calculated by the following formula: (m1-m0) / m0×100%, where, m0 represents the mass of the cathode material at 25°C during the heating process; m1 represents the mass of the cathode material at a temperature of 400°C during the heating process.

7. The cathode material according to any one of claims 1 to 6, wherein, The volume average particle size Dv50 of the cathode material is 3 μm to 30 μm.

8. The cathode material according to any one of claims 1 to 7, wherein, The BET specific surface area of ​​the cathode material is 0.2 m². 2 / g to 5.0m 2 / g.

9. The cathode material according to any one of claims 1 to 8, wherein, The pH value of the positive electrode material is 7 to 13.

10. A method for preparing a positive electrode material, the method comprising: S1: Mix the cathode material precursor, lithium salt and optional reducing agent in a solvent to obtain a mixture; S2: React the mixture to obtain a cathode material, wherein the cathode material comprises lithium manganese oxide, and the X-ray diffraction pattern of the lithium manganese oxide includes a first diffraction peak with a 2θ diffraction angle between 18.2° and 18.6° and a second diffraction peak with a 2θ diffraction angle between 18.6° and 19.0°.

11. The preparation method according to claim 10, wherein, The chemical formula of the cathode material precursor includes: Li δ Mn 2-y M y O 4-k-z X z Wherein, 0.9≤δ≤1, 0≤y≤0.5, 0≤z≤1, 0≤k≤0.5; M includes one or more of Cu, Ni, Co, Mg, Ca, Ba, Zn, Fe, Ti, Zr, W, Nb, Al, B, P, Mo, V, Cr, and Si; X includes one or more of F, S, and Cl.

12. The preparation method according to claim 10 or 11, wherein, The molar ratio M2 of the cathode material precursor to the lithium salt is 0.5 ≤ M2 ≤ 15.

13. The preparation method according to any one of claims 10 to 12, wherein, In step S2, the reaction is carried out at a temperature of 10°C to 100°C; and / or, the reaction is carried out for 0.5 h to 30 h.

14. The preparation method according to any one of claims 10 to 13, wherein, In step S1, the cathode material precursor and lithium salt are mixed in a solvent to obtain a mixture, wherein the lithium salt comprises an oxidation potential of less than 2.9V vs. Li / Li + The reducing lithium salt.

15. The preparation method according to claim 14, wherein, The reducing lithium salt includes one or more of lithium sulfide, lithium iodide, lithium borohydride, or lithium hydrosulfide.

16. The preparation method according to claim 14 or 15, wherein, The concentration of the reducing lithium salt in the mixture is 0.01 mol / L to 5 mol / L; and / or The mass fraction of the cathode material precursor in the mixture is 1% to 75%.

17. The preparation method according to any one of claims 10 to 13, wherein, In step S1, the cathode material precursor, lithium salt and reducing agent are mixed in a solvent to obtain a mixture.

18. The preparation method according to claim 17, wherein, The lithium salt includes one or more of lithium carbonate, lithium chloride, lithium sulfate, lithium bisulfate, lithium acetate, lithium bromide, lithium nitrate, lithium phosphate, lithium sulfide, lithium iodide, lithium borohydride, or lithium hydrosulfide; and / or The reducing agent includes one or more of diethylene glycol, sodium borohydride, or sodium hydrosulfide.

19. The preparation method according to claim 17 or 18, wherein, The concentration of the reducing agent in the mixture is 0.01 mol / L to 5 mol / L; and / or The concentration of the lithium salt in the mixture is 0.01 mol / L to 5 mol / L; and / or The mass fraction of the cathode material precursor in the mixture is 1% to 75%.

20. A secondary battery, the secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer comprising the positive electrode material according to any one of claims 1 to 9 or the positive electrode material prepared by the method according to any one of claims 10 to 19.

21. An electrical device comprising the secondary battery of claim 20.

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