Lithium manganese oxide materials, secondary batteries and electrical devices

Abstract

This application relates to a lithium manganese oxide material, its preparation method, a secondary battery, and an electrical device. In the differential scanning calorimetry (DSC) spectrum of the lithium manganese oxide material, the integral area T of the endothermic peak satisfies: T ≤ 50 J / g. The DSC testing process is as follows: under a protective gas atmosphere, the temperature is increased from -20℃ to 20℃ at a rate of 5℃ / min. The concentration of Ovs in this lithium manganese oxide material is maintained at a low level, thereby improving the structural stability of the lithium manganese oxide material. When applied to the preparation of secondary batteries, it can improve the cycle performance of the secondary batteries.

Description

[0001] This application is a divisional application of Chinese invention patent application filed by the applicant on November 3, 2023, entitled "Lithium manganese oxide material and preparation method thereof, secondary battery and power device", application number 202311452306.6. Technical Field

[0002] This invention relates to the field of battery technology, and in particular to a lithium manganese oxide material and its preparation method, a secondary battery, and an electrical device. Background Technology

[0003] Secondary batteries are increasingly widely used due to their clean and renewable characteristics. They mainly rely on the movement of active ions such as lithium ions between the positive and negative electrodes to generate electrical energy.

[0004] Lithium manganese oxide cathode materials are considered one of the ideal materials for power battery fabrication due to their abundant resources, low cost, environmental friendliness, and high safety. However, traditional lithium manganese oxide cathode materials have low structural stability, which leads to accelerated capacity decay during repeated charge and discharge cycles, reducing the cycle life of secondary batteries.

[0005] As people's demand for rechargeable batteries increases, traditional lithium manganese oxide cathode materials are finding it increasingly difficult to meet these needs and require further improvement. Summary of the Invention

[0006] Therefore, it is necessary to provide a lithium manganese oxide material and its preparation method, a secondary battery and an electrical device, with the aim of improving the cycle performance of the secondary battery.

[0007] In a first aspect, this application provides a lithium manganese oxide material, wherein in the differential scanning calorimetry (DSC) spectrum of the lithium manganese oxide material, the integral area T of the endothermic peak satisfies: 0 < T ≤ 50 J / g;

[0008] The testing process for the differential scanning calorimetry is as follows:

[0009] Under a protective gas atmosphere, the temperature is increased from -20℃ to 20℃ at a rate of 5℃ / min.

[0010] Extensive research and development, as well as actual production, have revealed that even when the macroscopic composition of lithium manganese oxide materials is the same, the structural stability of lithium manganese oxide materials is not entirely the same. This is especially true when applied to the preparation of secondary batteries, where the cycle performance of secondary batteries varies significantly. After conducting extensive experimental investigations into the composition, crystal phase, and microstructure of lithium manganese oxide materials, it was found that when the macroscopic composition of lithium manganese oxide materials is the same, the lower the content of oxygen vacancy defects (Ovs) in the lithium manganese oxide materials, the smaller the endothermic peak area in its differential scanning calorimetry spectrum, and the higher the cycle performance of the secondary battery.

[0011] Therefore, by controlling the upper limit of the integral area T of the endothermic peak in the differential scanning calorimetry spectrum of lithium manganese oxide material, the concentration of Ovs in lithium manganese oxide material is kept at a low level, thereby improving the structural stability of lithium manganese oxide material. When applied to the preparation of secondary batteries, it can improve the cycle performance of secondary batteries.

[0012] In some of these embodiments, 5 J / g ≤ T ≤ 50 J / g.

[0013] In some embodiments, the temperature range of the endothermic peak is 1°C to 20°C.

[0014] The temperature range in which the endothermic peak of the above-mentioned lithium manganese oxide material appears is 1℃~20℃. When integrating the endothermic peak, the temperature range of integration is 1℃~20℃.

[0015] In some embodiments, the composition of the lithium manganese oxide material satisfies: Li (1+a) Mn (2-x) M x O (4-δ) ;

[0016] Wherein, M includes one or more of Mg, Al, Fe, Ca, Zr, Y, Nb, Mo, Cr, W, V, Tc, Co and Ni, -0.3≤a≤0.2, 0≤x≤0.05, 0<δ≤0.005.

[0017] In some embodiments, the lithium manganese oxide material has a spinel phase.

[0018] A second aspect of this application provides a method for preparing lithium manganese oxide material, comprising the following steps:

[0019] The raw materials for preparation are provided according to the stoichiometric ratio of the corresponding components in the lithium manganese oxide material, including: lithium source and other component raw materials;

[0020] Under an oxygen-containing atmosphere, a portion of the lithium source and the other raw materials are subjected to a first sintering treatment to obtain a precursor;

[0021] The precursor and the remaining lithium source are subjected to a second sintering treatment under an oxygen-containing atmosphere to prepare the lithium manganese oxide material;

[0022] The first sintering process includes a constant temperature holding procedure, while the second sintering process is carried out under variable temperature conditions, which include a sequential heating and cooling procedure.

[0023] In the above-mentioned method for preparing lithium manganese oxide material, the lithium source is added in two stages, and the sintering temperature is controlled after each addition of lithium source. The first sintering process uses a constant temperature holding program to allow the cell and grain to grow fully, resulting in a precursor with a relatively complete crystal structure and relatively stable lattice oxygen. Then, the remaining lithium source is added, and a second sintering process is carried out under specific variable temperature conditions. This further improves the crystal structure and reduces the probability of lattice oxygen detachment. Through the synergistic effect of these factors, the concentration of Ovs in the prepared lithium manganese oxide material is maintained at a low level, thereby improving the structural stability of the lithium manganese oxide material. When applied to the preparation of secondary batteries, it can improve the cycle performance of the secondary batteries.

[0024] In some embodiments, the first sintering process satisfies at least one of the following conditions (a) to (b):

[0025] (a) The temperature of the constant temperature holding process in the first sintering treatment is 500℃~850℃.

[0026] (b) The duration of the constant temperature holding process in the first sintering treatment is 5h to 20h.

[0027] By regulating the temperature of the constant-temperature holding process during the first sintering treatment, the integrity of the precursor structure can be further improved.

[0028] In some embodiments, the heating process is as follows:

[0029] First, the temperature is increased from room temperature to 300℃~550℃ at the first heating rate, and then increased to 600℃~850℃ at the second heating rate.

[0030] Wherein, the first heating rate is greater than the second heating rate.

[0031] By adjusting specific temperature control programs, the probability of lattice oxygen detachment can be further reduced.

[0032] In some embodiments, the heating process satisfies at least one of the following conditions (a) to (b):

[0033] (a) The first heating rate is 1℃ / min to 10℃ / min;

[0034] (b) The second heating rate is 0.15℃ / min to 2.5℃ / min.

[0035] In some embodiments, the cooling procedure is as follows:

[0036] First, cool down to 300℃~550℃ at the first cooling rate, then cool down to room temperature at the second cooling rate;

[0037] Wherein, the first cooling rate is less than the second cooling rate.

[0038] In some embodiments, the cooling process satisfies at least one of the following conditions (a) to (b):

[0039] (a) The first cooling rate is 0.15℃ / min to 2.5℃ / min;

[0040] (b) The second cooling rate is 1℃ / min to 10℃ / min.

[0041] In some embodiments, the molar ratio of lithium element in a portion of the lithium source to that in the remainder of the lithium source is (3-11):1.

[0042] In some embodiments, the molar ratio of lithium element in a portion of the lithium source to that in the remainder of the lithium source is (3-9):1.

[0043] By adjusting the molar amount of lithium source added twice, it can better coordinate with the specific sintering temperature control program, thereby further improving the crystal structure and reducing the probability of lattice oxygen desorption.

[0044] In some embodiments, the other component raw materials include a manganese source and an M source, wherein M includes one or more of Li, Mg, Al, Fe, Ca, Zr, Y, Nb, Mo, Cr, Li, W, V, Tc, Co, and Ni.

[0045] A third aspect of this application provides a lithium manganese oxide material, which is prepared using the method for preparing lithium manganese oxide material of the second aspect.

[0046] A fourth aspect of this application provides a positive electrode sheet, the positive electrode sheet comprising a current collector and a positive electrode active layer disposed on the surface of the current collector, the positive electrode active layer comprising a lithium manganese oxide material of the first aspect or a lithium manganese oxide material of the third aspect.

[0047] A fifth aspect of this application provides a secondary battery, the secondary battery comprising the lithium manganese oxide material of the first aspect or the positive electrode sheet of the third or fourth aspect.

[0048] A sixth aspect of this application provides an electrical device comprising a secondary battery as described in the fifth aspect. Attached Figure Description

[0049] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0050] Figure 1 This is a schematic diagram of one embodiment of a battery cell;

[0051] Figure 2 yes Figure 1 Exploded view;

[0052] Figure 3 This is a schematic diagram of one embodiment of the battery pack;

[0053] Figure 4 yes Figure 3 Exploded view;

[0054] Figure 5 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source;

[0055] Figure 6 The X-ray diffraction patterns of lithium manganese oxide materials prepared in Example 1 and Comparative Example 1 are shown in (A) and (B).

[0056] Figure 7 The differential scanning calorimetry (DSC) spectra of lithium manganese oxide materials prepared in Example 1 and Comparative Example 1 are shown in comparison. (a) is the differential scanning calorimetry (DSC) spectrum of lithium manganese oxide material prepared in Example 1, and (b) is the differential scanning calorimetry (DSC) spectrum of lithium manganese oxide material prepared in Comparative Example 1.

[0057] Figure 8 Here are the charge and discharge curves of the button cell prepared in Example 1, (c) is the charging curve, and (d) is the discharging curve.

[0058] Figure 9 The graph shows the capacity retention rate of the batteries prepared in Example 1 and Comparative Example 1 during charge-discharge cycles.

[0059] Explanation of reference numerals in the attached figures:

[0060] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Individual battery cell; 41. Housing; 42. Electrode assembly; 43. Cover plate; 5. Electrical device. Detailed Implementation

[0061] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0062] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0063] In this application, unless otherwise specified, "room temperature" generally refers to 4℃~30℃, and preferably 20±5℃.

[0064] Extensive research and development, as well as actual production, have revealed that even when the macroscopic composition of lithium manganese oxide materials is the same, the structural stability of lithium manganese oxide materials is not entirely the same. This is especially true when applied to the preparation of secondary batteries, where the cycle performance of secondary batteries varies significantly. After conducting extensive experimental investigations into the composition, crystal phase, and microstructure of lithium manganese oxide materials, it was found that when the macroscopic composition of lithium manganese oxide materials is the same, the lower the content of oxygen vacancy defects (Ovs) in the lithium manganese oxide materials, the smaller the area of ​​the endothermic peak in its differential scanning calorimetry spectrum, and the higher the cycle performance of the secondary battery.

[0065] In traditional technology, lithium manganese oxide materials are often prepared by high-temperature solid-state sintering. This method involves mixing and grinding raw materials such as manganese and lithium sources according to the component ratio of lithium manganese oxide materials, and then sintering them at high temperature.

[0066] High-temperature solid-state methods have advantages such as simple operation, readily available raw materials, and ease of industrialization. However, their sintering process suffers from problems such as excessive reduction of lattice oxygen detachment and high oxygen vacancy (Ovs) content in the product. Those skilled in the art have consistently attempted to improve the stability of lithium manganese oxide materials through element doping, but the substantial improvement has been limited and industrialization has been difficult.

[0067] During long-term actual production and exploration, it was accidentally discovered that the detachment of lattice oxygen during high-temperature solid-state sintering is related to the addition method of lithium salt source and sintering method.

[0068] Thus, after extensive exploration, the lithium manganese oxide material and its preparation method as described in this application were obtained.

[0069] One embodiment of this application provides a lithium manganese oxide material, wherein the integral area T of the endothermic peak in the differential scanning calorimetry (DSC) spectrum of the lithium manganese oxide material satisfies: 0 < T ≤ 50 J / g; the testing process of the differential scanning calorimetry is as follows:

[0070] Under a protective gas atmosphere, the temperature is increased from -20℃ to 20℃ at a rate of 5℃ / min.

[0071] By controlling the upper limit of the integral area T of the endothermic peak in the differential scanning calorimetry spectrum of lithium manganese oxide material, the concentration of Ovs in lithium manganese oxide material is kept at a low level, thereby improving the structural stability of lithium manganese oxide material. When applied to the preparation of secondary batteries, it can improve the cycle performance of secondary batteries.

[0072] Understandably, differential scanning calorimetry (DSC) spectra are obtained using DSC. Specifically, the temperature conditions during the test are controlled by a temperature control program in computer software. The relationship between the power difference between the sample and the reference material input into the instrument and the temperature is measured. The obtained data is directly fed back to the computer software, and the DSC spectrum is obtained after processing. In the DSC spectrum, upward-pointing peaks represent endothermic peaks, and downward-pointing peaks represent exothermic peaks. Integration of endothermic peaks can be performed directly using the computer program.

[0073] In some of these embodiments, 5 J / g ≤ T ≤ 50 J / g.

[0074] In the above "5J / g≤T≤50J / g", the value of T includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 5J / g, 10J / g, 15J / g, 20J / g, 25J / g, 30J / g, 35J / g, 40J / g, 45J / g, 50J / g; or any range consisting of two values, for example, it can be 5J / g~50J / g, 5J / g~45J / g, 5J / g~40J / g, 5J / g~35J / g, 5J / g~30J / g, 5J / g~25J / g, 5J / g~20J / g, 5J / g~10J / g.

[0075] In some of these embodiments, the temperature range of the endothermic peak is 1°C to 20°C.

[0076] The temperature range in which the endothermic peak of the above-mentioned lithium manganese oxide material appears is 1℃~20℃. When integrating the endothermic peak, the temperature range of integration is 1℃~20℃.

[0077] In some embodiments, a coin cell is made using a positive electrode, a lithium sheet, a separator, and an electrolyte.

[0078] The positive electrode active layer in the positive electrode sheet comprises the aforementioned lithium manganese oxide material, carbon black SP, carbon nanotubes, and polyvinylidene fluoride in a mass ratio of 94:1.5:0.5:3.

[0079] The electrolyte consists of LiPF6 and a solvent, which is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1.

[0080] The diaphragm is made of polyolefin.

[0081] The above-mentioned button cells were charged and discharged at 0.1C to obtain charge and discharge curves.

[0082] In the charge-discharge curves, the total discharge specific capacity in the 3.0V–3.4V potential range is DC1, and the total discharge specific capacity in the 2.8V–4.3V potential range is DC2, 0.001. <DC1 / DC2<0.02。

[0083] Specifically, with 0.1C (setting 1C = 0.1A·g) -1 A constant current of a certain magnitude is used to perform charge and discharge tests, and charge and discharge curves are obtained. The vertical axis of the discharge curve is voltage, and the horizontal axis is discharge capacity. DC2 is the difference between the horizontal axis value corresponding to voltage 4.3V and the horizontal axis value corresponding to voltage 2.8V. Similarly, DC1 is the difference between the horizontal axis value corresponding to voltage 3.4V and the horizontal axis value corresponding to voltage 3.0V.

[0084] Further research revealed that the oxygen vacancy defect (Ovs) content in lithium manganese oxide materials is positively correlated with the DC1 to DC2 ratio obtained under specific conditions. That is, by controlling the upper limit of DC1 / DC2, the concentration of Ovs in lithium manganese oxide materials is maintained at a low level, thereby improving the structural stability of lithium manganese oxide materials. When applied to the preparation of secondary batteries, it can improve the cycle performance of secondary batteries.

[0085] In some of these embodiments, 0.002 <DC1 / DC2<0.02。

[0086] In some embodiments, the composition of the lithium manganese oxide material satisfies: Li (1+a) Mn (2-x) M x O (4-δ) .

[0087] Wherein, M includes one or more of Mg, Al, Fe, Ca, Zr, Y, Nb, Mo, Cr, W, V, Tc, Co and Ni, -0.3≤a≤0.2, 0≤x≤0.05, 0<δ≤0.005.

[0088] In the above "0≤x≤0.05", the value of x includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiment and the following point values: 0, 0.01, 0.02, 0.03, 0.04, 0.05; or any range of two values, such as: 0~0.04, 0.01~0.02, 0.03~0.04, 0.03~0.05.

[0089] In the above "0<δ≤0.005", the value of δ includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiment and the following point values: 0.001, 0.002, 0.003, 0.004, 0.005; or any range consisting of two values, such as: 0.001~0.002, 0.001~0.003, 0.001~0.004, 0.001~0.005, 0.002~0.005, 0.003~0.005.

[0090] In the above "-0.3≤a≤0.2", the value of 'a' includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: -0.3, -0.25, -0.2, -0.15, -0.1, -0.05, 0, 0.1, 0.15, 0.2; or any range consisting of two values, such as: -0.3~-0.1, -0.3~0, -0.3~-0.1, -0.3~0.15, -0.3~0.2, -0.2~-0.1, -0.2~0, -0.2~-0.1, -0.2~0.15, 0~0.1, 0~0.15, 0~0.2.

[0091] In some of these embodiments, the lithium manganese oxide material has a spinel phase.

[0092] According to an embodiment of this application, a method for preparing lithium manganese oxide material is provided, comprising the following steps S10 to S20.

[0093] Step S10: Provide the raw materials for preparation according to the stoichiometric ratio of the corresponding components in the lithium manganese oxide material, including: lithium source and other component raw materials.

[0094] In some embodiments, the stoichiometric ratio of the corresponding components in the lithium manganese oxide material satisfies: Li (1+a) Mn (2-x) M x O4.

[0095] The range of values ​​for M and x is the same as above, and will not be repeated here.

[0096] It is understandable that when feeding materials in step S10, it should be done according to Li. (1+a) Mn (2-x) M x The stoichiometric ratio of O4 added during the preparation process varies due to the presence of oxygen vacancies, specifically affecting the stoichiometric ratio of oxygen atoms produced. (1+a) Mn (2-x) M x O (4-δ) The ranges of values ​​for a, x, and δ are the same as above, and will not be repeated here.

[0097] Step S20: Under an oxygen-containing atmosphere, a portion of the lithium source and other raw materials are subjected to a first sintering treatment to obtain a precursor.

[0098] In some embodiments, other component raw materials include manganese source and M source.

[0099] M includes one or more of Li, Mg, Al, Fe, Ca, Zr, Y, Nb, Mo, Cr, W, V, Tc, Co, and Ni.

[0100] In some embodiments, the molar ratio of lithium source, manganese source and M source is (0.6-0.95):(1.95-1.99):(0.01-0.05).

[0101] In this application, the lithium source, manganese source, and M source may be lithium source compounds, manganese source compounds, and M source compounds commonly used in the art. Examples of lithium source, manganese source, and M source are given below, but are not limited to the following types.

[0102] The lithium source can be at least one of lithium salt compounds, lithium oxides, and lithium hydroxides; further, it can include at least one of lithium oxides, lithium hydroxides, lithium carbonates, lithium oxalates, lithium nitrates, and lithium borates; specifically, it can include at least one of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium borate.

[0103] The manganese source can be at least one of manganese salt compounds, manganese oxides, and manganese hydroxides; further, it can include at least one of manganese oxides, manganese hydroxides, manganese carbonates, manganese oxalates, and manganese nitrates; specifically, it can include at least one of manganese hydroxide, manganese carbonate, manganese nitrate, and manganese oxide.

[0104] The M source can be at least one of M-containing salt compounds, M-containing oxides, and M-containing hydroxides; further, it can include at least one of M-containing oxides, M-containing hydroxides, M-containing carbonates, M-containing oxalates, M-containing nitrates, etc.; for example, at least one of magnesium acetate, calcium carbonate, aluminum nitrate, hydroxide, and zirconium oxide.

[0105] Step S30: Under an oxygen-containing atmosphere, the precursor and the remaining lithium source are subjected to a second sintering treatment to prepare lithium manganese oxide material.

[0106] The first sintering process includes a constant temperature holding procedure, while the second sintering process is carried out under variable temperature conditions, which include a sequential heating and cooling procedure.

[0107] In the above-mentioned method for preparing lithium manganese oxide material, the lithium source is added in two stages, and the sintering temperature is controlled after each addition of lithium source. The first sintering process uses a constant temperature holding program to allow the cell and grain to grow fully, resulting in a precursor with a relatively complete crystal structure and relatively stable lattice oxygen. Then, the remaining lithium source is added, and a second sintering process is carried out under specific variable temperature conditions. This further improves the crystal structure and reduces the probability of lattice oxygen detachment. Through the synergistic effect of these factors, the concentration of Ovs in the prepared lithium manganese oxide material is maintained at a low level, thereby improving the structural stability of the lithium manganese oxide material. When applied to the preparation of secondary batteries, it can improve the cycle performance of the secondary batteries.

[0108] It should be noted that the above-mentioned "continuous heating and cooling procedures" do not include any heat preservation procedures in between; in other words, there are no heat preservation procedures during the heating procedure, no heat preservation procedures during the cooling procedure, and no heat preservation procedures during the transition between the heating and cooling procedures.

[0109] In some embodiments, the temperature of the isothermal holding process in the first sintering treatment is 500°C to 850°C.

[0110] In some embodiments, the isothermal holding process during the first sintering treatment lasts for 5 to 20 hours.

[0111] By regulating the temperature of the constant-temperature holding process during the first sintering treatment, the integrity of the precursor structure can be further improved.

[0112] The values ​​in "500℃~850℃" above include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃; or any range consisting of any two values, such as: 500℃~550℃, 500℃~650℃, 500℃~750℃, 600℃~650℃, 600℃~750℃, 600℃~850℃.

[0113] The values ​​in "5h~20h" above include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h; or any range consisting of two values, such as: 5h~20h, 10h~20h, 5h~15h, 10h~15h.

[0114] In some embodiments, the heating process is as follows: first, the temperature is increased from room temperature to 300°C to 550°C at a first heating rate, and then increased to 600°C to 850°C at a second heating rate.

[0115] The first heating rate is greater than the second heating rate.

[0116] By adjusting specific temperature control programs, the probability of lattice oxygen detachment can be further reduced.

[0117] In some embodiments, the first heating rate is 1°C / min to 10°C / min.

[0118] In some embodiments, the second heating rate is 0.15°C / min to 2.5°C / min.

[0119] In the above "1℃ / min~10℃ / min", the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min; or any range consisting of two values, such as: 1℃ / min~10℃ / min, 1℃ / min~9℃ / min, 1℃ / min~8℃ / min, 1℃ / min~5℃ / min, 3℃ / min~10℃ / min, 5℃ / min~10℃ / min, 5℃ / min~8℃ / min, 3℃ / min~6℃ / min.

[0120] The values ​​in "0.15℃ / min~2.5℃ / min" include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 0.15℃ / min, 0.5℃ / min, 1℃ / min, 1.15℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min; or any range consisting of two values, such as: 0.5℃ / min~2.5℃ / min, 1℃ / min~2.5℃ / min, 1℃ / min~2℃ / min, 0.15℃ / min~2℃ / min, 0.15℃ / min~1.5℃ / min, 0.15℃ / min~1℃ / min.

[0121] In some embodiments, the cooling process is as follows: first, the temperature is lowered to 300°C to 550°C at a first cooling rate, and then lowered to room temperature at a second cooling rate.

[0122] The first cooling rate is less than the second cooling rate.

[0123] In some embodiments, the room temperature is 4°C to 30°C; further, the room temperature is 20±5°C.

[0124] In some embodiments, the first cooling rate is 0.15°C / min to 2.5°C / min.

[0125] In some embodiments, the second cooling rate is 1°C / min to 10°C / min.

[0126] In the above "1℃ / min~10℃ / min", the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min; or any range consisting of two values, such as: 1℃ / min~10℃ / min, 1℃ / min~9℃ / min, 1℃ / min~8℃ / min, 1℃ / min~5℃ / min, 3℃ / min~10℃ / min, 5℃ / min~10℃ / min, 5℃ / min~8℃ / min, 3℃ / min~6℃ / min.

[0127] The values ​​in "0.15℃ / min~2.5℃ / min" include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 0.15℃ / min, 0.5℃ / min, 1℃ / min, 1.15℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min; or any range consisting of two values, such as: 0.5℃ / min~2.5℃ / min, 1℃ / min~2.5℃ / min, 1℃ / min~2℃ / min, 0.15℃ / min~2℃ / min, 0.15℃ / min~1.5℃ / min, 0.15℃ / min~1℃ / min.

[0128] In some embodiments, the molar ratio of lithium in a portion of the lithium source to that in the remainder of the lithium source is (3-11):1.

[0129] In some embodiments, the molar ratio of lithium in a portion of the lithium source to that in the remainder of the lithium source is (3-9):1.

[0130] By adjusting the molar amount of lithium source added twice, it can better coordinate with the specific sintering temperature control program, thereby further improving the crystal structure and reducing the probability of lattice oxygen desorption.

[0131] In the above "(3~11):1", the value includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 11:1, 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1; or any range of two values, such as: (3~8):1, (3~7):1, (3~6):1, (3~5):1, (3~4):1, (4~9):1, (4~8):1, (4~7):1, (4~6):1, (5~9):1, (5~8):1, (5~7):1, (5~6):1, (6~9):1, (6~8):1, (6~7):1.

[0132] In some embodiments, prior to the first sintering process, a first mixing process is included, in which a portion of the lithium source and other component raw materials are mixed; further, the first mixing process is carried out in a solvent.

[0133] In some embodiments, the solvent includes an alcoholic organic solvent having 1 to 4 carbon atoms; it may include at least one of methanol, ethanol, and propanol.

[0134] In some embodiments, in the first mixing process, the volume ratio of solvent to solid component is (5-15):1.

[0135] In some embodiments, the first mixing process takes 500 to 700 minutes.

[0136] In some embodiments, the first mixing process is carried out using a ball mill.

[0137] After the first mixing treatment step and before the first sintering treatment step, the mixture after the first mixing treatment is further dried to remove the solvent.

[0138] Furthermore, the drying process employs vacuum drying; specifically, the drying temperature is 100℃~150℃, and the pressure is 100pa.

[0139] In some embodiments, prior to the second sintering process, a step of second mixing of the precursor with the remaining lithium source is included; further, the second mixing process is carried out in a solvent.

[0140] In some embodiments, the solvent includes an alcoholic organic solvent having 1 to 4 carbon atoms; it may include at least one of methanol, ethanol, and propanol.

[0141] In some embodiments, in the second mixing process, the volume ratio of solvent to solid component is (5-15):1.

[0142] In some embodiments, the second mixing process takes 500 to 700 minutes.

[0143] In some embodiments, the second mixing process is carried out using a ball mill.

[0144] After the second mixing treatment step and before the second sintering treatment step, a drying treatment step is also included to remove the solvent from the mixed mixture.

[0145] Furthermore, the drying process employs vacuum drying; specifically, the drying temperature is 100℃~150℃, and the pressure is 100pa.

[0146] In some of these embodiments, the “oxygen-containing atmosphere” can be air, oxygen-enriched air, or a pure oxygen atmosphere.

[0147] In some of these embodiments, the oxygen volume content in the aforementioned "oxygen-containing atmosphere" is greater than or equal to 50%.

[0148] In some of these embodiments, the oxygen volume content in the aforementioned "oxygen-containing atmosphere" is greater than or equal to 60%.

[0149] In some of these embodiments, the oxygen volume content in the aforementioned "oxygen-containing atmosphere" is 60% to 99.9%.

[0150] Another embodiment of this application provides a lithium manganese oxide material, which is prepared by the above-described method for preparing lithium manganese oxide.

[0151] The lithium manganese oxide material prepared by the above method maintains a low concentration of Ovs, thereby improving the structural stability of the lithium manganese oxide material. When applied to the preparation of secondary batteries, it can improve the cycle performance of the secondary batteries.

[0152] In one embodiment of this application, a positive electrode sheet is also provided, the positive electrode sheet including a current collector and a positive electrode active layer disposed on the surface of the current collector, the composition of the positive electrode active layer including the above-mentioned lithium manganese oxide material or the lithium manganese oxide material prepared by the above-mentioned method of preparing lithium manganese oxide material.

[0153] In some embodiments, the weight ratio of lithium manganese oxide material in the positive electrode active layer is 80wt% to 100wt% based on the total weight of the positive electrode active layer.

[0154] In any embodiment of this application, the positive electrode active layer further comprises a positive electrode conductive agent and a positive electrode binder.

[0155] The aforementioned positive electrode conductive agent can be a commonly used conductive agent in the art, including but not limited to at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene. Specifically, it may include at least one of conductive carbon black (Super-P, abbreviated as SP), conductive graphite SFG-6, conductive graphite KS-6, acetylene black, superconducting carbon black with a branched structure, Ketjen black (ECP), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNTs), and graphene and their composite conductive agents.

[0156] Based on the total weight of the positive electrode active layer, the weight ratio of the positive electrode conductive agent in the positive electrode active layer is 0–20 wt%.

[0157] In any embodiment of this application, the binder of the above-mentioned positive electrode binder may be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, hydrogenated nitrile rubber, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS), and fluorinated acrylate resin.

[0158] Based on the total weight of the positive electrode active layer, the weight ratio of the positive electrode binder in the positive electrode active layer is 0–30 wt%.

[0159] In any embodiment of this application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a current collector, and then performing processes such as drying and cold pressing to obtain the positive electrode sheet. The solid content of the positive electrode slurry is 40wt% to 80wt%, and the viscosity at room temperature is adjusted to 5000 mPa·s.

[0160] The positive electrode slurry is coated onto the surface of the positive electrode current collector at a pressure of ~25000 mPa·s, dried, and then cold-pressed using a cold rolling mill to form a positive electrode sheet; the compacted density of the positive electrode sheet is 3.0 g / cm³. 3 ~3.6g / cm 3 3.3g / cm³ is an option. 3 ~3.5g / cm 3 The formula for calculating compacted density is:

[0161] Compacted density = Surface density of the single-sided positive electrode active material layer / (Thickness of the single-sided positive electrode active material layer - Thickness of the current collector).

[0162] One embodiment of this application provides a secondary battery, which includes lithium manganese oxide material or a positive electrode sheet.

[0163] Secondary batteries also include negative electrode plates, separators, and electrolytes. Examples of negative electrode plates, separators, and electrolytes are given below, including but not limited to the following.

[0164] Electrolyte: Generally, electrolyte includes electrolyte salts and solvents.

[0165] In some embodiments, the electrolyte salt may be selected from electrolyte salts commonly used in the art, such as lithium-ion electrolyte salts.

[0166] As an example, lithium-ion electrolyte salts include, but are not limited to, one or more of the following: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0167] In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0168] In some embodiments, the concentration of the electrolyte salt in the electrolyte is typically 0.5 mol / L to 15 mol / L.

[0169] 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.

[0170] Separator: The separator is placed between the positive electrode and the negative electrode.

[0171] The type of separator used in this application can be any known porous structure separator with good chemical and mechanical stability.

[0172] 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. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0173] The thickness of the diaphragm is controlled between 2 μm and 15 μm; optionally, the thickness of the diaphragm is controlled between 2 μm and 13 μm.

[0174] Negative electrode sheet: The negative electrode sheet can be a negative electrode sheet used in various secondary battery systems in this field.

[0175] In some embodiments, the battery is a lithium metal secondary battery, and the negative electrode can be a negative electrode known in the art that can be used in lithium metal batteries.

[0176] In some embodiments, the negative electrode is directly made of lithium-containing metal sheet.

[0177] In another embodiment, the negative electrode includes a lithium-containing metal layer and a conductive layer stacked together.

[0178] Furthermore, the lithium-containing technology in the lithium-containing metal sheet and lithium-containing metal layer can be lithium metal or an alloy formed by lithium metal and other metal or non-metal elements.

[0179] Furthermore, other metals include at least one of tin (Sn), zinc (Zn), aluminum (Al), magnesium (Mg), silver (Ag), gold (Au), gallium (Ga), indium (In), and foil (Pt); non-metallic elements include at least one of boron (B), carbon (C), and silicon (Si).

[0180] In some embodiments, the conductive layer may be copper foil.

[0181] In any embodiment of this application, the above-mentioned negative electrode sheet can be prepared by directly pressing a lithium-containing metal sheet to obtain a negative electrode sheet, or by stacking and pressing the above-mentioned lithium-containing metal layer and conductive layer together.

[0182] In some embodiments, the battery is a lithium-ion secondary battery, and the negative electrode can be a negative electrode known in the art that can be used in lithium-ion batteries.

[0183] In some embodiments, the negative electrode includes a current collector and a negative electrode active layer loaded on the surface of the current collector.

[0184] The components of the negative electrode active layer include negative electrode active materials.

[0185] The aforementioned negative electrode active material can be any commonly used negative electrode active material described in this application.

[0186] In any embodiment of this application, the aforementioned negative electrode active material includes at least one of the following: mesophase carbon microspheres, graphite, glassy carbon, carbon nanotubes, carbon-carbon composite materials, carbon fibers, hard carbon, soft carbon, silicon-based materials, tin-based materials, magnesium-based materials, and iron-based materials.

[0187] Optionally, specific examples of the above-mentioned negative electrode active materials include, but are not limited to, at least one of the following: mesophase carbon microspheres, natural graphite, artificial graphite, graphene, glassy carbon, carbon nanotubes, carbon fibers, hard carbon, soft carbon, iron oxide, tin oxide, silicon oxide, magnesium oxide, silicon-carbon composites, lithium metal, and lithium metal alloys.

[0188] In any embodiment of this application, the mass percentage of the above-mentioned negative electrode active material in the negative electrode active layer is 70% to 100%.

[0189] In any embodiment of this application, the components of the above-mentioned negative electrode active layer further include a negative electrode conductive agent and a negative electrode binder.

[0190] In any embodiment of this application, the aforementioned negative electrode conductive agent can be a commonly used conductive material in the art, including but not limited to at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene. Specifically, it may include at least one of conductive carbon black (super-p, abbreviated as SP), conductive graphite SFG-6, conductive graphite KS-6, acetylene black, superconducting carbon black with a branched structure, Ketjen black (ECP), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNTs), and graphene and their composite conductive agents.

[0191] Based on the total weight of the negative electrode active layer, the weight ratio of the negative electrode conductive agent in the negative electrode active layer is 0–20 wt%.

[0192] The aforementioned negative electrode binder can be a commonly used binder in the art, and can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethyl methacrylate (PMAA), and carboxymethyl chitosan (CMCS).

[0193] Based on the total weight of the negative electrode active layer, the weight ratio of the negative electrode binder in the negative electrode active layer is 0–30 wt%.

[0194] In any embodiment of this application, the negative electrode active layer may optionally include other additives, such as thickeners, such as sodium carboxymethyl cellulose (CMC-Na). Based on the total weight of the negative electrode active layer, the weight ratio of other additives in the negative electrode active layer is 0 to 15 wt%.

[0195] In any embodiment of this application, the current collector in the negative electrode can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil.

[0196] Composite current collectors may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. Composite current collectors can be formed by forming a metal material on a polymer substrate.

[0197] In some embodiments, the metallic material is selected from any one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys.

[0198] In some embodiments, the polymer material substrate includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0199] In any embodiment of this application, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0200] In some embodiments, the solvents mentioned above include, but are not limited to, water.

[0201] In some embodiments, the solid content of the negative electrode slurry is 30wt% to 70wt%, and the viscosity at 25°C is adjusted to 2000mPa·s to 10000mPa·s.

[0202] In some embodiments, the areal density of the negative electrode active material layer contained in the negative electrode sheet is 0.005 g / cm³. 2 ~0.03g / cm 2 .

[0203] The areal density of the negative electrode active material layer = the mass of the negative electrode active material layer / the area of ​​the negative electrode active material layer in the negative electrode sheet.

[0204] The secondary battery of this application can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 Here is a square-structured battery cell 4 as an example.

[0205] In some embodiments, refer to Figure 2 The outer casing may include a housing 41 and a cover plate 43. The housing 41 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 41 has an opening communicating with the receiving cavity, and the cover plate 43 can be placed over the opening to close the receiving cavity.

[0206] The positive electrode, negative electrode, and separator can be formed into electrode assembly 42 by winding or stacking processes. Electrode assembly 42 is encapsulated within a receiving cavity. Electrolyte is immersed in electrode assembly 42. The number of electrode assemblies 42 contained in a single battery cell 4 can be one or more, and can be adjusted according to requirements.

[0207] This application also provides an electrical device that includes the aforementioned secondary battery.

[0208] Furthermore, in the aforementioned electrical device, the secondary battery can exist in the form of a single battery cell, or it can be further assembled into a battery pack.

[0209] Figure 3 and Figure 4Here is an example of a battery pack 1. The battery pack 1 includes a battery box and one or more battery cells 4 disposed in the battery box. The battery box includes an upper box 2 and a lower box 3, the upper box 2 being able to cover the lower box 3 and form an enclosed space for the battery cells 4.

[0210] Multiple battery cells 4 can be arranged in the battery box in any way.

[0211] The aforementioned battery or the battery pack assembled therefrom can be used as a power source for an electrical device or as an energy storage unit for an electrical device.

[0212] The aforementioned electrical devices may include, but are not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc.

[0213] In some embodiments, the mobile device may be a mobile phone or a laptop computer, etc.

[0214] In some embodiments, electric vehicles include, but are not limited to: pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0215] Figure 5 This is an example of an electrical device 5. This electrical device 5 can be 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 electrical device 5, a battery pack can be used.

[0216] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use batteries as their power source.

[0217] The present application will be described below with reference to specific embodiments, but the present application is not limited to the following embodiments. It should be understood that the appended claims summarize the scope of the present application. Under the guidance of the concept of the present application, those skilled in the art should realize that certain changes made to the various embodiments of the present application will be covered by the spirit and scope of the claims of the present application.

[0218] The following are specific examples.

[0219] Example 1

[0220] S1: Preparation of lithium manganese oxide materials

[0221] (1) Weigh the raw materials as follows:

[0222] 5.036 g of lithium hydroxide monohydrate, 26.286 g of manganese hydroxide and 0.641 g of magnesium acetate were weighed and mixed. Ethanol with a volume of 10 times the total solid volume was added. The mixture was wet-milled in an ultra-high-power ball mill for 600 minutes, and then vacuum-dried at 120 °C and 100 Pa to obtain the mixture.

[0223] (2) The mixture was heated to 600°C in an atmosphere furnace and held for 10 hours for the first sintering treatment. During the sintering process, the oxygen volume content in the sintering atmosphere was controlled to be 66%. After sintering, the mixture was cooled and crushed to obtain the precursor.

[0224] (3) Add 1.259g of lithium hydroxide monohydrate to the precursor, wet grind and mix evenly using an ultra-high-energy ball mill, vacuum dry, and then place it in an oxygen-enriched air atmosphere furnace with an oxygen volume content of 66% for a second sintering treatment. The process is as follows: heat from room temperature to 450℃ at a first heating rate of 5℃ / min, then continue heating to 700℃ at a second heating rate of 0.3℃ / min, then reduce the sintering temperature to 450℃ at a first cooling rate of 0.3℃ / min, and finally reduce to room temperature at a second cooling rate of 5℃ / min to obtain lithium manganese oxide material.

[0225] The molar ratio of lithium element in lithium hydroxide monohydrate added in step (1) to that in lithium hydroxide monohydrate added in step (3) is denoted as H. Please refer to Table 1 for details.

[0226] S2: Preparation of the positive electrode sheet

[0227] The lithium manganese oxide material, conductive agent, carbon nanotubes, and polyvinylidene fluoride prepared above were combined in a mass ratio of 94:1.5:0.5:3 to prepare a positive electrode slurry. This slurry was coated onto a 13 μm thick Al foil, and after vacuum drying at 120℃, cold pressing, and slitting, a positive electrode sheet was obtained, with an areal density of 15 mg / cm³. 2 .

[0228] S3: Preparation of electrolyte

[0229] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of EC:EMC:DEC = 1:1:1 to obtain an organic solvent. Then, fully dried lithium source LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0230] S4: Select polyethylene film as the separator for lithium-ion batteries.

[0231] S5: Negative Electrode: Graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are added to deionized water in a weight ratio of 97:0.5:1.25:1.25 and mixed for 6 hours to obtain a negative electrode slurry. This slurry is then uniformly coated onto the negative electrode current collector and dried to obtain a negative electrode sheet with an areal density of 8 mg / cm³. 2 .

[0232] S6: Assembly of lithium-ion batteries: Stack the positive electrode, separator, and negative electrode in sequence, with the separator positioned between the anode and cathode to provide isolation, and then wind them to obtain the bare cell. Place the bare cell in the outer packaging, inject 10g of prepared electrolyte, and then proceed with processes such as encapsulation, electrolyte injection, formation, and venting to obtain the lithium-ion battery.

[0233] S7: Test

[0234] Characterization tests of lithium manganese oxide materials:

[0235] (1) X-ray diffraction test

[0236] The lithium manganese oxide material prepared above was subjected to X-ray diffraction testing using a Bruker D8 Discover instrument. The measurement conditions were as follows: Cu target, tube voltage 40V, tube current 40mA, scanning speed 2° / min, 2θ scanning range 15°~70°, step size 0.02°, emission slit (DS) 1mm, anti-scattering slit (SS) 8mm, and graphite monochromator.

[0237] The X-ray diffraction pattern of the lithium manganese oxide material prepared above is as follows: Figure 6 As shown in (A), it exhibits spinel phase characteristics.

[0238] (2) Differential Scanning Calorimetry (DSC)

[0239] The prepared lithium manganese oxide material was tested using differential scanning calorimetry (DSC): Nitrogen gas was passed through the protective atmosphere at a flow rate of 50 mL / min. The temperature was increased from -20℃ to 20℃ at a rate of 5℃ / min, and then allowed to cool naturally. The resulting differential scanning calorimetric (DSC) spectrum was obtained, as shown below. Figure 7 As shown in curve (a), the horizontal axis represents temperature (Temp), and the vertical axis represents the power flowing to each gram of sample (DSC, Mw / mg). Figure 7 Because the endothermic peak is small and the vertical axis is compressed, the endothermic peak is not obvious. After widening the vertical axis, the endothermic peak appears in the range of 1℃ to 20℃. The area of ​​the endothermic peak is scanned and integrated. The integration temperature range is 1℃ to 20℃, and the integration area is denoted as T, as shown in Table 1.

[0240] The area of ​​the endothermic peak on the DSC spectrum is positively correlated with the oxygen vacancy content of lithium manganese oxide material. The smaller the value of the integrated area, the lower the oxygen vacancy content of the lithium manganese oxide material.

[0241] Battery performance test:

[0242] 1. Specific capacity test: Using the above-mentioned positive electrode as the positive electrode and the lithium sheet as the negative electrode, assemble a coin cell. During the test, a rate of 0.1C is used (set 1C = 0.1A·g). -1 A charge-discharge test was conducted using a current of a certain magnitude, and the charge-discharge curve is shown below. Figure 8 As shown, (d) is the discharge curve and (c) is the charging curve. The charge and discharge capacity of the battery was tested in the range of 2.8 to 4.3V. The total discharge specific capacity of the discharge plateau in the potential range of 3.0V to 3.4V is denoted as DC1, which is the difference between the horizontal axis value corresponding to 3.4V and the horizontal axis value corresponding to 3.0V in the discharge curve. The total discharge specific capacity of the discharge plateau in the potential range of 4.3V to 2.8V is denoted as DC2, which is the difference between the horizontal axis value corresponding to 4.3V and the horizontal axis value corresponding to 2.8V in the discharge curve. The value of DC1 / DC2 is positively correlated with the oxygen vacancy content of the lithium manganese oxide material. The smaller the value of DC1 / DC2, the lower the oxygen vacancy content of the lithium manganese oxide material. DC1 / DC2 is denoted as γ. Please refer to Table 1 for details.

[0243] 2. Cyclic performance test: At 25°C, the lithium-ion battery obtained in step S6 was subjected to a cycle test according to the following procedure: at a 1C rate (set 1C = 0.1A·g). -1 Perform charge-discharge tests, setting the voltage range to 2.8V to 4.3V. One charge-discharge cycle is considered one complete cycle. Record the initial capacity at this point. Repeat this process for 100 cycles, recording the cell's capacity after 100 cycles. The percentage of the capacity after 100 cycles to the initial capacity is denoted as P. 100 . Please see Table 1 for details.

[0244] The capacity retention curve of the lithium-ion battery prepared in Example 1 under 2.8V to 4.3V charge-discharge cycles is shown below. Figure 9 As shown, the horizontal axis represents the number of cycles, in cycles, and the vertical axis represents the capacity retention rate.

[0245] Examples 2-4

[0246] Examples 2 to 4 are basically the same as Example 1, except that in step S1, while keeping the total amount of lithium hydroxide monohydrate added in step (1) and lithium hydroxide monohydrate added in step (3) the same as in Example 1, the mass of lithium hydroxide monohydrate added in step (1) and lithium hydroxide monohydrate added in step (3) is changed, thereby changing H.

[0247] The other steps are the same as in Example 1. Please refer to Table 1 for specific parameters.

[0248] Example 5

[0249] Example 5 is basically the same as Example 1, except that: in step S1, the mass of lithium hydroxide monohydrate added in steps (1) and (3) is 5.099g and 1.825g respectively, and magnesium acetate is not added in step (1) to obtain lithium manganese oxide material.

[0250] The other steps are the same as in Example 1. Please refer to Table 1 for specific parameters.

[0251] Example 6

[0252] Example 6 is basically the same as Example 1, except that in step S1, in step (1), 0.641g magnesium acetate is replaced with 1.688g aluminum nitrate.

[0253] The other steps are the same as in Example 1. Please refer to Table 1 for specific parameters.

[0254] Example 7

[0255] Example 7 is basically the same as Example 1, except that in step S1, in step (1), 0.641g of magnesium acetate is replaced with 0.555g of zirconium oxide.

[0256] The other steps are the same as in Example 1. Please refer to Table 1 for specific parameters.

[0257] Examples 8-13

[0258] Examples 8 to 13 are basically the same as Example 1, except that in step S1, the isothermal temperature or time of the first sintering treatment in step (2) is changed.

[0259] The other steps are the same as in Example 1. Please refer to Table 1 for specific parameters.

[0260] Examples 14-17

[0261] Examples 14-17 are basically the same as Example 1, except that in step S1, the cutoff temperature during the second sintering process in step (4) is changed to either the cutoff temperature at the first heating rate or the cutoff temperature at the second heating rate. Specifically, in Example 14, the temperature is increased from room temperature to 350°C at a first heating rate of 5°C / min; in Example 15, the temperature is increased from room temperature to 550°C at a first heating rate of 5°C / min; in Example 16, the temperature is increased to 650°C at a second heating rate of 0.3°C / min; and in Example 17, the temperature is increased to 800°C at a second heating rate of 0.3°C / min.

[0262] The other steps are the same as in Example 1. Please refer to Table 1 for specific parameters.

[0263] Examples 18-22

[0264] Examples 18-22 are basically the same as Example 1, except that in step S1, the first heating rate or the second heating rate is changed during the second sintering process in step (4).

[0265] The other steps are the same as in Example 1. Please refer to Table 1 for specific parameters.

[0266] Examples 23-26

[0267] Examples 23-26 are basically the same as Example 1, except that in step S1, the first cooling rate or the second cooling rate is changed during the second sintering process in step (4).

[0268] The other steps are the same as in Example 1. Please refer to Table 1 for specific parameters.

[0269] Comparative Example 1

[0270] Comparative Example 1 is basically the same as Example 1, except that: step S1 is as follows:

[0271] (1) Weigh 6.295 g of lithium hydroxide monohydrate, 26.286 g of manganese hydroxide and 0.641 g of magnesium acetate respectively, mix them, add 10 times the total volume of solids of ethanol, wet grind and mix them in an ultra-powerful ball mill for 600 minutes, and then vacuum dry them at 120°C and 100 Pa to obtain the mixture.

[0272] (2) The mixture was heated to 600°C in an atmosphere furnace and held for 10 hours for the first sintering treatment. During the sintering process, the oxygen volume content in the sintering atmosphere was controlled to be 66%. After sintering, the mixture was cooled and crushed to obtain the precursor.

[0273] (3) The precursor was placed in an oxygen-enriched air atmosphere furnace with an oxygen volume content of 66% for a second sintering treatment. The process was as follows: the temperature was raised from room temperature to 450°C at a first heating rate of 5°C / min, then raised to 700°C at a second heating rate of 0.3°C / min, the sintering temperature was lowered to 450°C at a first cooling rate of 0.3°C / min, and finally lowered to room temperature at a second cooling rate of 5°C / min to obtain lithium manganese oxide material.

[0274] The other steps are the same as in Example 1. Please refer to Table 1 for specific parameters.

[0275] The X-ray diffraction pattern of the lithium manganese oxide material prepared in Comparative Example 1 is as follows: Figure 6As shown in (B), it also exhibits spinel phase characteristics; the differential scanning calorimetry (DSC) spectrum of the lithium manganese oxide material prepared in Comparative Example 1 is shown in the figure below. Figure 7 As shown in curve (b), the capacity retention curve of the lithium-ion battery prepared in Comparative Example 1 during cyclic charge-discharge at 2.8V to 4.3V is as follows. Figure 9 As shown.

[0276] The other steps are the same as in Example 1. Please refer to Table 1 for specific parameters.

[0277] Comparative Example 2

[0278] Comparative Example 2 is basically the same as Example 1, except that step S1 is as follows:

[0279] (1) Weigh 5.036g of lithium hydroxide monohydrate, 26.286g of manganese hydroxide and 0.641g of magnesium acetate respectively, mix them, add 10 times the total volume of solids of ethanol, wet grind and mix them in an ultra-powerful ball mill for 600 minutes, and then vacuum dry them at 120℃ and 100pa to obtain the mixture.

[0280] (2) Then add 1.259g of lithium hydroxide monohydrate to the mixture, wet grind and mix evenly with an ultra-powerful ball mill, vacuum dry and place in an oxygen-enriched air atmosphere furnace with an oxygen volume content of 66% for sintering treatment. The process is as follows: heat from room temperature to 800℃ at a heating rate of 5℃ / min and hold for sintering for 10h to obtain lithium manganese oxide material.

[0281] The other steps are the same as in Example 1. Please refer to Table 1 for specific parameters.

[0282] Comparative Example 3

[0283] Comparative Example 3 is basically the same as Example 1, except that step S1 is as follows:

[0284] (1) Weigh 5.036g of lithium hydroxide monohydrate, 26.286g of manganese hydroxide and 0.641g of magnesium acetate respectively, mix them, add 10 times the total volume of solids of ethanol, wet grind and mix them in an ultra-powerful ball mill for 600 minutes, and then vacuum dry them at 120℃ and 100pa to obtain the mixture.

[0285] (2) The mixture was subjected to a first sintering treatment in an atmosphere furnace as follows: the temperature was increased from room temperature to 450°C at a first heating rate of 5°C / min, then increased to 700°C at a second heating rate of 0.3°C / min, the sintering temperature was reduced to 450°C at a first cooling rate of 0.3°C / min, and finally reduced to room temperature at a second cooling rate of 5°C / min. The precursor was crushed and obtained. During the sintering process, the oxygen volume content in the sintering atmosphere was controlled to be 66%.

[0286] (3) Add 1.259g of lithium hydroxide monohydrate to the precursor, wet grind and mix evenly with an ultra-powerful ball mill, vacuum dry and then place it in an oxygen-enriched air atmosphere furnace with an oxygen volume content of 66% for a second sintering treatment: heat to 600℃ and hold for sintering for 10h to obtain lithium manganese oxide material.

[0287] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0288] The relevant parameters and performance test results of each embodiment and comparative example are shown in Table 1. Among them, the molar ratio of lithium element in lithium hydroxide monohydrate added in step (1) to lithium element in lithium hydroxide monohydrate added in step (3) is denoted as H; the first heating rate, the second heating rate, the first cooling rate and the second cooling rate in step (3) are denoted as Y1, Y2, Y3 and Y1 respectively, the cutoff temperature when heating at the first heating rate is denoted as X1, and the cutoff temperature when heating at the second heating rate is denoted as X2.

[0289] Table 1

[0290]

[0291] Analysis of the data in Table 1 shows that: in this application, lithium manganese oxide materials with the integral area of ​​the endothermic peak in the differential scanning calorimetry spectrum within a specific range, or lithium manganese oxide materials prepared by the preparation method of lithium manganese oxide materials in this application, can improve the cycle performance of secondary batteries.

[0292] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0293] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A lithium manganese oxide material, characterized in that, In the differential scanning calorimetry (DSC) spectrum of the lithium manganese oxide material, the integral area T of the endothermic peak satisfies: 0 < T ≤ 50 J / g; The testing process for the differential scanning calorimetry is as follows: Under a protective gas atmosphere, the temperature is increased from -20℃ to 20℃ at a rate of 5℃ / min. The composition of the lithium manganese oxide material satisfies: Li (1+a) Mn (2-x) M x O (4-δ) ; Wherein, M includes one or more of Mg, Al, Fe, Ca, Zr, Y, Nb, Mo, Cr, W, V, Tc, Co and Ni, -0.3≤a≤0.2, 0≤x≤0.05, 0<δ≤0.

005.

2. The lithium manganese oxide material as described in claim 1, characterized in that, 5J / g≤T≤50J / g.

3. The lithium manganese oxide material as described in claim 1, characterized in that, 5J / g≤T≤30J / g.

4. The lithium manganese oxide material as described in claim 1, characterized in that, 5J / g≤T≤10J / g.

5. The lithium manganese oxide material according to any one of claims 1 to 4, characterized in that, The M includes one or more of Mg, Al, and Zr.

6. The lithium manganese oxide material according to any one of claims 1 to 4, characterized in that, M is Mg.

7. The lithium manganese oxide material according to any one of claims 1 to 4, characterized in that, 0≤a≤0.2, 0.01≤x≤0.05, 0.001<δ≤0.

003.

8. The lithium manganese oxide material according to any one of claims 1 to 4, characterized in that, The temperature range of the endothermic peak is 1℃~20℃.

9. The lithium manganese oxide material according to any one of claims 1 to 4, characterized in that, The lithium manganese oxide material has a spinel phase.

10. The lithium manganese oxide material according to any one of claims 1 to 4, characterized in that, The lithium manganese oxide material meets the following conditions: A button cell is made using a positive electrode, lithium foil, separator, and electrolyte. The positive electrode active layer in the positive electrode sheet comprises lithium manganese oxide material, carbon black SP, carbon nanotubes and polyvinylidene fluoride in a mass ratio of 94:1.5:0.5:

3. The electrolyte comprises LiPF6 and a solvent, wherein the concentration of LiPF6 is 1 mol / L; the solvent is a mixture of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:

1. The diaphragm is made of polyolefin. The button cell was charged and discharged at 0.1C to obtain its charge-discharge curve, where 1C = 0.1 A·g -1 ; In the charge-discharge curve, the total discharge capacity in the potential range of 3.0V to 3.4V is DC1, and the total discharge capacity in the potential range of 2.8V to 4.3V is DC2, 0.001 <DC1 / DC2<0.02。 11. The lithium manganese oxide material as described in claim 10, characterized in that, 0.002 <DC1 / DC2<0.02。 12. A positive electrode plate, characterized in that, The positive electrode includes a current collector and a positive electrode active layer disposed on the surface of the current collector, wherein the composition of the positive electrode active layer includes lithium manganese oxide material as described in any one of claims 1 to 11.

13. A secondary battery, characterized in that, The secondary battery includes lithium manganese oxide material as described in any one of claims 1 to 11 or a positive electrode sheet as described in claim 12.

14. An electrical appliance, characterized in that, The electrical device includes the secondary battery as described in claim 13.

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