Porous lithium-rich manganese-based positive electrode material and preparation method thereof

Abstract

The invention relates to a porous lithium-rich manganese-based positive electrode material and a preparation method thereof, belongs to the technical field of lithium ion battery positive electrode materials, solves the problems of poor anion reaction kinetics and low ion electron conductivity in the prior art, and comprises the following steps: S1, mixing a nickel manganese hydroxide precursor with a lithium salt to obtain mixed powder; and S2, placing the mixed powder in a tubular furnace into which air atmosphere is introduced, and carrying out multi-step sintering to obtain the porous lithium-rich manganese-based positive electrode material, the step S2 specifically comprises the steps that S2.1, the mixed powder is heated to the first platform temperature from the room temperature according to the first heating speed and kept for a period of heat preservation time, then the mixed powder is heated to the second platform temperature according to the second heating speed and kept for a period of heat preservation time, and the first heating speed is larger than the second heating speed; step S2.2, reducing the temperature from the second platform temperature to a third platform temperature according to the first cooling speed, and keeping the temperature for a period of heat preservation time; and cooling to room temperature to obtain the porous lithium-rich manganese-based positive electrode material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion battery cathode materials, and particularly relates to a porous lithium-rich manganese-based cathode material and a preparation method thereof. BACKGROUND

[0002] With the rapid development of portable electronic devices and electric vehicles, the market has put forward higher requirements for high-energy-density, high-portability and long-endurance energy storage systems. Lithium ion batteries have become the current mainstream high-performance energy storage devices due to their excellent characteristics such as high operating voltage and high specific capacity, and are widely used in portable electronics and vehicles. However, the traditional cathode material is limited in further improving the energy density of lithium ion batteries due to its large molar mass and limited relative lithium content. The lithium-rich manganese-based cathode material introduces a reversible oxygen anion redox mechanism on the basis of cation redox reaction, which can achieve a specific capacity exceeding that of conventional materials, and is therefore considered as one of the potential materials for breaking the energy density limit of lithium batteries. However, the capacity of the lithium-rich manganese-based material is greatly limited due to the relatively poor anion reaction kinetics and low ion-electron conductivity of the lithium-rich material. In addition, the poor solid-solid contact between the lithium-rich material and the solid-state electrolyte further limits the capacity of the cathode material. Moreover, the material is prone to release lattice oxygen under high-voltage operation, leading to irreversible changes in structure and enhanced interface side reactions, thereby affecting the cycle stability and safety of the battery. The morphology design of the lithium-rich manganese-based material can optimize the interface contact between the lithium-rich material and the solid-state electrolyte, and is conducive to the construction of the ion-electron conduction network in the composite cathode system, which may be an effective way to solve the poor reaction kinetics of the lithium-rich cathode material in the full solid-state battery.

[0003] Therefore, there is a need in the art for a new lithium-rich manganese-based cathode material with high specific capacity and high stability to improve the performance of the assembled full solid-state battery system. SUMMARY

[0004] In view of the above problems, the present application provides a porous lithium-rich manganese-based cathode material and a preparation method thereof. The purpose of the present application is to overcome the deficiencies and shortcomings of the prior art, and to provide a synthesis method for preparing submicron porous lithium-rich manganese-based cathode material by multi-step sintering, as well as its application in full solid-state batteries. The method has high production efficiency, and the prepared submicron porous lithium-rich manganese-based cathode material has uniform distribution and high crystallinity, high first-cycle capacity, high first efficiency and good cycle performance in solid-state batteries; and solves the problems of delayed reaction kinetics and solid-solid interface contact of lithium-rich materials in solid-state batteries.

[0005] According to one embodiment of the present application, a porous lithium-rich manganese-based cathode material preparation method is provided, comprising the following steps:

[0006] Step S1, mixing the nickel-manganese hydroxide precursor and lithium salt by using a mixer to obtain a mixed powder;

[0007] Step S2, placing the obtained mixed powder in a tube furnace with air atmosphere, and performing multi-step sintering to obtain a porous lithium-rich manganese-based positive electrode material;

[0008] In step S2, it specifically includes:

[0009] Step S2.1, heating the mixed powder from room temperature to a first plateau temperature at a first heating rate, keeping at the first plateau temperature for a certain holding time, then heating from the first plateau temperature to a second plateau temperature at a second heating rate, keeping at the second plateau temperature for a certain holding time, and the first heating rate is greater than the second heating rate;

[0010] Step S2.2, cooling from the second plateau temperature to a third plateau temperature at a first cooling rate, keeping at the third plateau temperature for a certain holding time, and then cooling from the third plateau temperature to room temperature to obtain the porous lithium-rich manganese-based positive electrode material.

[0011] Optionally, in step S1, during the mixing process, the rotation speed of the mixer is set to 10 rmp / min-50 rmp / min, and the mixing time is 10 h-25 h.

[0012] Optionally, in step S1, the lithium salt used is one or more of lithium hydroxide, lithium carbonate and lithium chloride.

[0013] Optionally, in step S1, the nickel-manganese hydroxide precursor and the lithium salt are mixed in a molar ratio range of 1:1.1-1:1.5, and the lithium salt is in excess of 5%-25% based on the mixing.

[0014] Optionally, in step S2.1, the first heating rate is set to a range of 5℃ / min-10℃ / min, the first plateau temperature is set to a range of 300℃-500℃, and the holding time at the first plateau temperature is set to a range of 5h-10h.

[0015] Optionally, in step S2.1, the second heating rate is set to a range of 1℃ / min-5℃ / min, the second plateau temperature is set to a range of 900℃-1100℃, and the holding time at the second plateau temperature is set to a range of 10h-20h.

[0016] Optionally, in step S2.2, the first cooling rate is set to a range of 2℃ / min-10℃ / min, the third plateau temperature is set to a range of 300℃-500℃, and the holding time at the third plateau temperature is set to a range of 5h-10h.

[0017] The porous lithium-rich manganese-based positive electrode material prepared by the preparation method of the porous lithium-rich manganese-based positive electrode material according to the embodiment of the present application has a chemical formula of Li x Ni y Mn z O2, wherein 1.1<=x<=1.3, 0.2<=y<=0.5, and 0.4<=z<=0.7.

[0018] Optionally, the porous lithium-rich manganese-based positive electrode material has secondary particles formed by stacking long strip-shaped primary particles, the particle size of the primary particles ranges from 0.1 to 1.5 microns, the particle size of the secondary particles ranges from 2 to 10 microns, the pore size of the porous structure in the secondary particles ranges from 0.5 to 3 microns, and the particle size ratio of the secondary particles to the primary particles ranges from 1.4 to 5.

[0019] Compared with the prior art, the porous lithium-rich manganese-based positive electrode material and the preparation method thereof provided by the present application have at least the following beneficial effects.

[0020] (1) The morphology of the precursor is well controlled through multi-step sintering, and the porous lithium-rich manganese-based positive electrode material prepared can inherit the morphology of the precursor, while maintaining the uniformity of the particle size and the regularity of the spherical shape, the nano-scale porous network structure is constructed in the particle, the high capacity potential of the lithium-rich manganese-based material in the all-solid-state battery is stimulated, and the high-energy-density all-solid-state battery is realized.

[0021] (2) The multi-step sintering in the sintering process can inhibit the excessive growth of the crystal grains and improve the density, and can reduce the generation of impurities and the defect density. At the same time, the sintering in the tube furnace can realize closed or flowing atmosphere sintering, control the oxygen partial pressure in the sintering process, prevent the structure from collapsing caused by oxygen loss or oxygen release, and obtain the lithium-rich manganese-based material with stable structure.

[0022] (3) The present application directly uses nickel-manganese hydroxide as the precursor to mix with lithium salt, and then sinter to prepare the porous lithium-rich manganese-based positive electrode material, which does not need to consider the problem of carbon release compared with the carbonate precursor.

[0023] (4) The preparation process of the present application is reasonable in design, the reaction is easy to control, the prepared product has good consistency, and the mechanical strength is higher. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. The features and advantages of the present application can be more clearly understood by referring to the drawings. The drawings are schematic and should not be construed as any limitation on the present application. Those skilled in the art can obtain other drawings according to the drawings without any creative effort.

[0025] Figure 1 X-ray diffraction pattern of the porous lithium-rich manganese-based positive electrode material prepared in Example 1 of a method for preparing a porous lithium-rich manganese-based positive electrode material according to an embodiment of the present application.

[0026] Figure 2 Cross-sectional scanning electron microscope image of the porous lithium-rich manganese-based positive electrode material prepared in Example 1.

[0027] Figure 3 Graph of the first cycle voltage specific capacity of a full solid-state battery assembled using the porous lithium-rich manganese-based positive electrode material prepared in Example 1, in a voltage range of 2.0-4.8 V at a 0.05 C rate current.

[0028] Figure 4 X-ray diffraction pattern of the porous lithium-rich manganese-based positive electrode material prepared in Example 2 of a method for preparing a porous lithium-rich manganese-based positive electrode material according to an embodiment of the present application.

[0029] Figure 5 Cross-sectional scanning electron microscope image of the porous lithium-rich manganese-based positive electrode material prepared in Example 2.

[0030] Figure 6 Graph of the first cycle voltage specific capacity of a full solid-state battery assembled using the porous lithium-rich manganese-based positive electrode material prepared in Example 2, in a voltage range of 2.0-4.8 V at a 0.05 C rate current.

[0031] Figure 7 X-ray diffraction pattern of the lithium-rich manganese-based positive electrode material prepared in the method of Comparative Example 1.

[0032] Figure 8 Scanning electron microscope image of the lithium-rich manganese-based positive electrode material prepared in the method of Comparative Example 1.

[0033] Figure 9 Graph of the first cycle voltage specific capacity of a full solid-state battery assembled using the materials obtained in Example 1 and Example 3, and Comparative Example 1, in a voltage range of 2.0-4.8 V at a 0.05 C rate current.

[0034] Figure 10 Graph of the cycle performance of a full solid-state battery assembled using the materials obtained in Example 1 and Example 3, and Comparative Example 1, in a voltage range of 2.0-4.8 V at a 0.5 C rate current. DETAILED DESCRIPTION

[0035] In order to enable a more clear understanding of the above-mentioned objects, features and advantages of the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0036] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, and therefore the scope of protection of the present application is not limited by the specific embodiments disclosed below.

[0037] A porous lithium-rich manganese-based positive electrode material and a preparation method thereof according to an embodiment of the present application are described in detail below with reference to the accompanying drawings.

[0038] The electrochemical performance of the lithium-rich manganese-based positive electrode material is improved by constructing an internal porous structure. The porous structure design can increase the specific surface area of the material at the micro level and form three-dimensional interconnected ion and electron transmission channels, thereby effectively improving the interface contact quality with the solid-state electrolyte. This structural advantage not only reduces the interface impedance and promotes the rapid transmission of lithium ions in the solid-solid interface, but also helps to reduce the problem of local reaction activity reduction caused by uneven internal stress distribution. By optimizing the particle size and morphology, the formation of polycrystalline porous particles is possible, and the porous structure can relieve the volume strain during cycling and release the accumulated internal stress, thereby inhibiting the generation of microcracks and improving the cycle life. As can be seen, the use of porous structure design is beneficial to the performance improvement of lithium-rich manganese positive electrode materials in all-solid-state lithium batteries.

[0039] The preparation method of the porous lithium-rich manganese-based positive electrode material according to the embodiment of the present application comprises the following steps.

[0040] In step S1, a nickel-manganese hydroxide precursor and a certain mass percentage of lithium salt are mixed using a mixer, wherein the rotational speed of the mixer is set to 10 rmp / min-50 rmp / min, and the mixing time is 10 h-25 h, to obtain a mixed powder.

[0041] The chemical formula of the nickel-manganese hydroxide precursor used in step S1 is Ni a Mn b (OH)2; wherein the component ratio of the nickel-manganese hydroxide precursor satisfies: 0.2≤a≤0.5, 0.5≤b≤0.8, and a+b=1. The nickel-manganese hydroxide precursor can be purchased commercially.

[0042] The lithium salt used in step S1 can include but is not limited to one or more of lithium hydroxide, lithium carbonate, and lithium chloride.

[0043] The nickel-manganese hydroxide precursor in step S1 is mixed with lithium salt in a certain molar ratio, and the ratio ranges from 1:1.1 to 1:1.5. In this mixing, the lithium salt is 5% to 25% in excess, that is, the amount of lithium salt prepared according to the molar ratio range is 5% to 25% in excess.

[0044] Through the above providing mode of the precursor, the morphology of the precursor is well controlled, thereby facilitating the preparation of the positive electrode material to maintain the uniformity of the particle size and the regularity of the spherical shape, while realizing the construction of the nano-scale porous network structure inside the particles, finally stimulating the high capacity potential of the lithium-rich manganese-based material in the full solid-state battery, and realizing the high energy density full solid-state battery. In addition, the nickel-manganese hydroxide is used as the precursor to mix with the lithium salt, and then sintered to prepare the porous lithium-rich manganese-based positive electrode material, which does not need to consider the problem of carbon release compared with the carbonate precursor.

[0045] In step S2, the mixed powder obtained in step S1 is placed in a tube furnace with an air atmosphere, and multi-step sintering is performed to obtain a porous lithium-rich manganese-based positive electrode material. In the sintering process, multi-step sintering is adopted to inhibit excessive grain growth, improve density, and ensure the generation of internal porous structure; to reduce the generation of impurities and defects, and stimulate the high capacity potential of the lithium-rich manganese-based material. This step S2 specifically includes the following steps.

[0046] In step S2.1, the mixed powder is heated from room temperature to a first platform temperature at a first heating rate, kept at the first platform temperature for a certain holding time, and then heated from the first platform temperature to a second platform temperature at a second heating rate, kept at the second platform temperature for a certain holding time. The first heating rate can be greater than the second heating rate. The first heating rate is fast, which can quickly cross the critical temperature of the precursor decomposition through rapid heating (5-10℃ / min), avoiding the retention of impurity carbonization caused by slow heating, and the appropriate rapid heating can reduce the residence time of the precursor in the low temperature zone, prevent pre-reaction caused by uneven heating for a long time, and promote the rapid decomposition of the binder, nitrate and other components in the precursor, generating a large amount of gas to form an initial pore framework in the material. The second heating rate is slow, which can avoid rapid grain growth at high temperature, maintain the nano-scale particle size, reduce lithium evaporation and cation mixing, and through slow gas escape and grain sintering in the high temperature zone, the initial pores are further connected and stabilized to form a porous structure.

[0047] In this embodiment, the first heating rate can range from 5℃ / min to 10℃ / min, the first platform temperature can range from 300℃ to 500℃, and the holding time at the first platform temperature can range from 5h to 10h.

[0048] The first temperature rising rate is set to quickly remove volatile components in the precursor, ensure uniform heating of the material, and avoid cracking and composition segregation caused by thermal stress. The above first temperature rising rate range can provide better reaction results. If the temperature rises too slowly below the lower limit of the range, the organic matter may not be completely decomposed. If the temperature rises too quickly above the upper limit of the range, thermal shock may occur, causing the precursor particles to break or the pore distribution to be uneven.

[0049] The first platform temperature is set to promote the preliminary crystallization of transition metal oxides and provide a structural template for high-temperature sintering. The above first platform temperature range setting can provide better reaction results. If the temperature is below 300°C, which is below the lower limit of the range, incomplete decomposition may occur, and residual impurities may hinder the formation of subsequent crystal phases. If the temperature is above 500°C, which is above the upper limit of the range, some lithium salts may react too early, causing uneven lithium distribution.

[0050] The first platform temperature holding time is set to ensure complete decomposition, ensure that the precursor is completely converted into an oxide, and stabilize the initial structure to avoid defects caused by structural mutations in the subsequent high-temperature stage. The above first platform temperature holding time range setting can ensure the above effects. If the holding time is shorter than the lower limit of the range, i.e., shorter than 5h, the decomposition may not be complete, affecting the purity of the material. If the holding time is longer than the upper limit of the range, i.e., longer than 10h, there is no significant additional benefit, resulting in a decrease in preparation efficiency.

[0051] In this embodiment, the second temperature rising rate range can be set to 1°C / min-5°C / min, the second platform temperature range can be set to 900°C-1100°C, and the second platform temperature holding time range can be set to 10h-20h.

[0052] The second temperature rising rate is set to control grain growth and reduce lithium evaporation. The above second temperature rising rate range setting can better ensure the above effects. If the second temperature rising rate is lower than the lower limit of the range, the temperature rising rate is too slow, which may prolong the process cycle. If the second temperature rising rate is higher than the upper limit of the range, the temperature rising rate is too fast, which may cause uneven grain size distribution.

[0053] The second platform temperature is set to form a stable crystal phase and improve electrochemical activity. The above second platform temperature range setting can better ensure the above effects. If the second platform temperature is lower than the lower limit of the range, i.e., the second platform temperature is lower than 900°C, incomplete crystallization may occur. If the second platform temperature is higher than the upper limit of the range, i.e., the second platform temperature is higher than 1100°C, lithium may evaporate severely, causing the composition to deviate from the design value.

[0054] The setting of the second plateau temperature holding time can ensure sufficient reaction and optimize the pore structure. The above range of the second plateau temperature holding time can better ensure the above effects. If the second plateau temperature holding time is shorter than the lower limit of the range, i.e. shorter than 10 h, the reaction will be incomplete and local components will be uneven; if the second plateau temperature holding time is longer than the upper limit of the range, i.e. longer than 20 h, the grains will grow excessively.

[0055] In step S2.2, continue to decrease the temperature from the second plateau temperature to a third plateau temperature at a first decreasing rate, hold at the third plateau temperature for a certain holding time, and then decrease the temperature from the third plateau temperature to room temperature to obtain the porous lithium-rich manganese-based positive electrode material. In this embodiment, the first decreasing rate can be set to a range of 2-10 ℃ / min, the third plateau temperature can be set to a range of 300-500 ℃, and the holding time at the third plateau temperature can be set to a range of 5-10 h.

[0056] The setting of the first decreasing rate can avoid thermal stress cracks and control phase transition. The above range of the first decreasing rate can better ensure the above effects. If the first decreasing rate is lower than the lower limit of the range, the first decreasing rate is too slow, there is no significant benefit, and the cost is increased; if the first decreasing rate is higher than the upper limit of the range, the first decreasing rate is too fast, which can cause material embrittlement.

[0057] The setting of the third plateau temperature can achieve annealing treatment, eliminate internal stress of high-temperature sintering, stabilize the lattice structure, and adjust oxygen vacancies. The range of the third plateau temperature can better ensure the above effects. If the third plateau temperature is lower than the lower limit of the range, i.e. below 300 ℃, the annealing effect will be poor; if the third plateau temperature is higher than the upper limit of the range, i.e. above 500 ℃, secondary phase transition can be induced.

[0058] The setting of the third plateau temperature holding time can fully release stress. The range of the third plateau temperature holding time can better ensure the above effects. If the third plateau temperature holding time is shorter than the lower limit of the range, i.e. shorter than 5 h, the stress release will be incomplete; if the third plateau temperature holding time is longer than the upper limit of the range, i.e. longer than 10 h, there is no obvious additional benefit, but the preparation efficiency is reduced.

[0059] According to another embodiment of the present application, there is also provided a porous lithium-rich manganese-based positive electrode material prepared by the preparation method described above. The porous lithium-rich manganese-based positive electrode material has secondary particles formed by stacking primary particles in a long strip-shaped lamellar shape, and the secondary particles have irregularly sized pore structures distributed therein. The primary particles are in a long strip-shaped lamellar shape, and the size of the primary particles is 0.1-1.5 μm; the size of the secondary particles is 2-10 μm, and the secondary particles have irregularly sized pore structures distributed therein, and the size of the pores of the pore structures is 0.5-3 μm. The ratio of the size of the secondary particles to the size of the primary particles is in the range of 1.4-5. The porous lithium-rich manganese-based positive electrode material can be used to assemble a full solid-state battery.

[0060] The chemical formula of the porous lithium-rich manganese-based positive electrode material prepared by the preparation method described above is Li x Ni y Mn z O2; wherein, 1.1≤x≤1.3, 0.2≤y≤0.5, and 0.4≤z≤0.7.

[0061] The embodiments of the present application are further described below through specific examples, so that a more comprehensive and in-depth understanding of the technical solutions of the present application can be obtained. It should be understood that these examples are only used to illustrate the specific embodiments of the present application, and do not constitute any limitation on the protection scope of the present application. In the examples and comparative examples described in the present application, the raw materials used are used under conventional conditions or according to the recommended conditions of their manufacturers, unless otherwise specified. The reagents and experimental instruments used are commercially available conventional reagents or general-purpose instruments, unless otherwise specified.

[0062] Example 1

[0063] Referring to Figures 1 to 3 The specific steps for preparing the porous lithium-rich manganese-based positive electrode material are as follows, using the example 1 of the preparation method of the porous lithium-rich manganese-based positive electrode material provided according to the embodiments of the present application.

[0064] In step S1, the nickel-manganese hydroxide precursor and lithium hydroxide are mixed in a molar ratio of 1:1.3. 12 g of nickel-manganese hydroxide precursor and 4.96 g of lithium hydroxide (20% excess of lithium hydroxide) are weighed and mixed uniformly using a mixer at a speed of 30 rmp / min for 20 h to obtain a mixed powder.

[0065] Step S2, transfer the mixed powder to a high-temperature-resistant corundum square boat with a size of 60*20*20mm, flatten it, draw it into blocks, and then transfer it to a tube furnace connected to an air atmosphere for sintering. After being heated to 500°C at a heating rate of 8°C / min, it is kept for 5h; then heated to 1000°C at a rate of 3°C / min and kept for 15h; then cooled to 500°C at a rate of 5°C / min and kept for 5h; finally, cooled to room temperature at a rate of 5°C / min. Sintering obtains a porous lithium-rich manganese-based positive electrode material.

[0066] Figure 1 is the X-ray diffraction pattern of the porous lithium-rich manganese-based positive electrode material prepared in Example 1, Figure 2 is the cross-sectional scanning electron microscope image of the lithium-rich manganese-based positive electrode material prepared in Example 1, Figure 3 is the first cycle voltage specific capacity result graph of the full solid-state battery assembled by the porous lithium-rich manganese-based positive electrode material prepared by the method of Example 1 in the voltage range of 2.0V-4.8V at a 0.05C rate current.

[0067] As shown in Figure 1 , the material prepared in Example 1 is indeed a lithium-rich manganese-based positive electrode material. Figure 2 As can be seen, the secondary particle size of the porous lithium-rich manganese-based material prepared in Example 1 is 2-3μm, and the inside is an irregularly distributed pore structure with a pore size of 1-1.5μm. As shown in Figure 3 , the porous lithium-rich manganese-based positive electrode material prepared in Example 1 is assembled into a full solid-state battery, which has a charge specific capacity of 294.7mAh / g and a discharge specific capacity of 251.5mAh / g in the first cycle under the working conditions of 0.05C, 45°C and a voltage range of 2.0-4.8V, and the first cycle coulombic efficiency is 85.3%.

[0068] Example 2

[0069] Referring to Figures 4 to 6 , Example 2 applies the porous lithium-rich manganese-based positive electrode material preparation method provided according to the embodiments of the present application, and the specific steps for preparing the porous lithium-rich manganese-based positive electrode material are as follows.

[0070] Step S1, mix the nickel-manganese hydroxide precursor with lithium hydroxide in a molar ratio of 1:1.2, weigh 12g of nickel-manganese hydroxide precursor, add 4.20g of lithium hydroxide (lithium hydroxide excess 10%), and mix it evenly using a mixer at a speed of 25rmp / min for 10h to obtain a mixed powder.

[0071] Step S2, transfer the mixed powder to a high-temperature-resistant corundum box with a size of 60*20*20mm, flatten it, and divide it into blocks, then transfer it to a tube furnace connected to an air atmosphere for sintering. Heat at a rate of 5°C / min to 450°C, then keep it at this temperature for 8h; then heat at a rate of 2°C / min to 1000°C, then keep it at this temperature for 12h; then cool at a rate of 5°C / min to 450°C and keep it at this temperature for 5h, and finally cool at a rate of 5°C / min to room temperature. Sintering obtains a porous lithium-rich manganese-based positive electrode material.

[0072] Figure 4 is the X-ray diffraction pattern of the porous lithium-rich manganese-based positive electrode material prepared in Example 2, Figure 5 is the cross-sectional scanning electron microscope image of the lithium-rich manganese-based positive electrode material prepared in Example 2, Figure 6 is the first cycle voltage specific capacity result graph of the porous lithium-rich manganese-based positive electrode material prepared by the method of Example 2 in the full solid-state battery in the voltage range of 2.0V-4.8V at a rate of 0.05C.

[0073] As shown in Figure 4 , the material prepared in Example 2 is indeed a lithium-rich manganese-based positive electrode material. Figure 5 As can be seen, the porous lithium-rich manganese-based material prepared in Example 2 has a secondary particle size of 2-3μm, and has irregularly distributed pore structures inside, with a pore size of 1-1.5μm. Figure 6 As shown in , the porous lithium-rich manganese-based positive electrode material prepared in Example 2 is assembled into a full solid-state battery, which has a charge specific capacity of 267.5mAh / g and a discharge specific capacity of 199.0mAh / g in the first cycle under the working conditions of 0.05C, 45°C, and a voltage range of 2.0-4.8V, and the first cycle coulombic efficiency is 74.4%.

[0074] Example 3

[0075] Example 3 applies the porous lithium-rich manganese-based positive electrode material preparation method according to the embodiment of the present application, and the specific steps for preparing the porous lithium-rich manganese-based positive electrode material are as follows.

[0076] Step S1, mix the nickel-manganese hydroxide precursor with lithium carbonate in a molar ratio of 1:1.25, weigh 12g of nickel-manganese hydroxide precursor, add 7.06g of lithium carbonate (lithium carbonate excess 15%), and mix it evenly using a mixer, the mixer speed is 20rmp / min, and the mixing time is 15h, to obtain a mixed powder.

[0077] Step S2, the mixed powder is transferred to a high-temperature-resistant corundum square boat with a size of 60*20*20mm, flattened, and divided into blocks, and then transferred to a tube furnace connected to an air atmosphere for sintering. After being heated to 400℃ at a heating rate of 6℃ / min from room temperature, it is kept for 10h; then heated to 950℃ at a rate of 5℃ / min, and kept for 10h; then cooled to 400℃ at a rate of 10℃ / min, and kept for 6h; finally, cooled to room temperature at a rate of 5℃ / min. The sintering obtains a porous lithium-rich manganese-based positive electrode material.

[0078] Example 4

[0079] Example 4 of the porous lithium-rich manganese-based positive electrode material preparation method provided according to the embodiments of the present application is applied, and the specific steps for preparing the porous lithium-rich manganese-based positive electrode material are as follows.

[0080] Step S1, the nickel-manganese hydroxide precursor is matched with the lithium salt in a molar ratio of 1:1.25, 12g of nickel-manganese hydroxide precursor is weighed, lithium hydroxide and lithium carbonate mixed lithium salt with a mass ratio of 1:1 are used as lithium salt, 7.25g of lithium hydroxide and 7.25g of lithium carbonate mixed lithium salt (mixed lithium salt excess 25%) are added respectively, and a mixer is used to mix them uniformly, the mixer speed is 50rmp / min, and the mixing time is 10h, to obtain a mixed powder.

[0081] Step S2, the mixed powder is transferred to a high-temperature-resistant corundum square boat with a size of 60*20*20mm, flattened, and divided into blocks, and then transferred to a tube furnace connected to an air atmosphere for sintering. After being heated to 400℃ at a heating rate of 6℃ / min from room temperature, it is kept for 10h; then heated to 950℃ at a rate of 5℃ / min, and kept for 10h; then cooled to 400℃ at a rate of 10℃ / min, and kept for 6h; finally, cooled to room temperature at a rate of 5℃ / min. The sintering obtains a porous lithium-rich manganese-based positive electrode material.

[0082] Example 5

[0083] Example 5 of the porous lithium-rich manganese-based positive electrode material preparation method provided according to the embodiments of the present application is applied, and the specific steps for preparing the porous lithium-rich manganese-based positive electrode material are as follows.

[0084] Step S1, the nickel-manganese hydroxide precursor is matched with lithium chloride in a molar ratio of 1:1.4, 12g of nickel-manganese hydroxide precursor is weighed, and 8.29g of lithium chloride (lithium chloride excess 5%) is added, a mixer is used to mix them uniformly, the mixer speed is 35rmp / min, and the mixing time is 18h, to obtain a mixed powder.

[0085] Step S2, the mixed powder is transferred to a high-temperature-resistant corundum box with a size of 60*20*20mm, flattened, and cut into blocks, and then transferred to a box furnace connected to an air atmosphere for sintering. After being heated to 300°C at a heating rate of 10°C / min and kept for 8h at room temperature, then heated to 900°C at a heating rate of 5°C / min and kept for 18h, then cooled to 300°C at a heating rate of 5°C / min and kept for 8h, and finally cooled to room temperature at a heating rate of 5°C / min. The sintering obtains the porous lithium-rich manganese-based positive electrode material.

[0086] Example 6

[0087] Example 6 is applied to the preparation method of the porous lithium-rich manganese-based positive electrode material according to the embodiment of the present application. The specific steps for preparing the porous lithium-rich manganese-based positive electrode material are as follows.

[0088] Step S1, the nickel-manganese hydroxide precursor is mixed with lithium carbonate at a molar ratio of 1:1.1. 12g of nickel-manganese hydroxide precursor is weighed, 6.48g of lithium carbonate (lithium carbonate excess 20%) is added, and a mixer is used to mix them uniformly, the mixer speed is 40rmp / min, and the mixing time is 20h, to obtain the mixed powder.

[0089] Step S2, the mixed powder is transferred to a high-temperature-resistant corundum box with a size of 60*20*20mm, flattened, and cut into blocks, and then transferred to a box furnace connected to an air atmosphere for sintering. After being heated to 300°C at a heating rate of 10°C / min and kept for 8h at room temperature, then heated to 900°C at a heating rate of 5°C / min and kept for 18h, then cooled to 300°C at a heating rate of 5°C / min and kept for 8h, and finally cooled to room temperature at a heating rate of 5°C / min. The sintering obtains the porous lithium-rich manganese-based positive electrode material.

[0090] Comparative Example 1

[0091] 1. 12g of nickel-manganese hydroxide precursor is weighed, the nickel-manganese hydroxide precursor is mixed with lithium carbonate at a molar ratio of 1:1.1, 5.94g of lithium carbonate (lithium carbonate excess 10%) is added, and a mixer is used to mix them uniformly, the mixer speed is 50rmp / min, and the mixing time is 20h, to obtain the mixed powder.

[0092] 2. The mixed powder is transferred to a high-temperature-resistant corundum box with a size of 60*20*20mm, flattened, and cut into blocks, and then transferred to a box furnace connected to an air atmosphere for sintering. After being heated to 300°C at a heating rate of 10°C / min and kept for 8h at room temperature, then heated to 900°C at a heating rate of 5°C / min and kept for 18h, then cooled to 300°C at a heating rate of 5°C / min and kept for 8h, and finally cooled to room temperature at a heating rate of 5°C / min. The sintering obtains the porous lithium-rich manganese-based positive electrode material.

[0093] Figure 7 X-ray diffraction pattern of the lithium-rich manganese-based positive electrode material prepared for Comparative Example 1 using the prior art lithium-rich manganese-based positive electrode material preparation method, Figure 8 Scanning electron microscope image of the lithium-rich manganese-based positive electrode material prepared for Comparative Example 1 using the method of Comparative Example 1. As Figure 7 shown, the material synthesized for Comparative Example 1 is a lithium-rich manganese-based material, but combined Figure 8 it can be seen that Comparative Example 1 failed to synthesize a structure with internal porosity.

[0094] Comparative Example 2

[0095] 1. 12 g of nickel-manganese hydroxide precursor was weighed out, the nickel-manganese hydroxide precursor was mixed with lithium hydroxide at a molar ratio of 1:1.5, 5.96 g of lithium hydroxide (25% excess of lithium hydroxide) was added, and a mixer was used to mix them until they were uniform, the mixer speed was 50 rmp / min, and the mixing time was 15 h, to obtain a mixed powder.

[0096] 2. The mixed powder was transferred to a high-temperature-resistant corundum square boat with a size of 60*20*20 mm, flattened, and divided into blocks, and then transferred to a box furnace with air atmosphere for sintering. After being heated to 400°C at a heating rate of 10°C / min, it was kept at this temperature for 5 h; then heated to 850°C at a rate of 8°C / min and kept at this temperature for 25 h; then cooled to 400°C at a rate of 12°C / min and kept at this temperature for 10 h, and finally cooled to room temperature at a rate of 5°C / min. Sintering obtained a lithium-rich manganese-based positive electrode material.

[0097] The lithium-rich manganese-based material synthesized using the prior art lithium-rich manganese-based positive electrode material preparation method of Comparative Example 2 still does not have an internal porous structure.

[0098] Figure 9 The first cycle specific capacity graph of the full solid-state battery composed of the porous lithium-rich manganese-based positive electrode material prepared in Example 1 and Example 3 of the present application, and the lithium-rich manganese-based positive electrode material prepared in Comparative Example 1, respectively, in the voltage range of 2.0-4.8V at a 0.05C rate current; Figure 10 The cycle performance result graph of the full solid-state battery composed of the porous lithium-rich manganese-based positive electrode material prepared in Example 1 and Example 3 of the present application, and the lithium-rich manganese-based positive electrode material of Comparative Example 1, respectively, in the voltage range of 2.0-4.8V at a 0.5C rate current.

[0099] Referring to Figure 9 ​​​​​​​​​​​​​​​​​​​The first circle discharge specific capacity of the all-solid-state batteries composed of Example 1 and Example 3 is 251.5 mAh / g and 236.7 mAh / g, respectively, which is higher than the first circle discharge specific capacity 220 mAh / g of the all-solid-state battery of Comparative Example 1. The first circle coulombic efficiency of the all-solid-state batteries composed of Example 1 and Example 3 is 85.3% and 81.0%, respectively, which is lower than the first circle coulombic efficiency 78.7% of the all-solid-state battery of Comparative Example 1. As shown in Table 2, the capacity retention rate of the all-solid-state batteries composed of Example 1 and Example 3 is 98.9% and 85.2%, respectively, which is higher than the capacity retention rate 60.8% of the all-solid-state battery of Comparative Example 1. Therefore, the all-solid-state batteries composed of Example 1 and Example 3 have improved cycle life. Figure 10

[0100] Therefore, it can be proved that, compared with the material obtained by the existing preparation method, the porous lithium-rich manganese-based positive electrode material prepared by the preparation method of the porous lithium-rich manganese-based positive electrode material provided by the embodiment of the application has better performance when applied to a solid-state battery, has higher capacity potential, realizes higher energy density, and has longer service life, etc.

[0101] All the optional technical solutions described above can be combined to form optional embodiments of the application, which will not be described one by one here.

[0102] It should be understood that the size of the serial number of each step in the above embodiments does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the application.

[0103] The above description is only a preferred embodiment of the application, but the protection scope of the application is not limited to this. Any changes or replacements within the technical scope disclosed by the application can be easily thought of by those skilled in the art, which should be covered within the protection scope of the application.​

Claims

1. A method for preparing a porous lithium-rich manganese-based cathode material, characterized in that, Includes the following steps: Step S1: The nickel-manganese hydroxide precursor and lithium salt are mixed using a mixer to obtain a mixed powder; Step S2: The obtained mixed powder is placed in a tube furnace with an air atmosphere and sintered in multiple steps to obtain a porous lithium-rich manganese-based cathode material. Step S2 specifically includes: Step S2.1: The mixed powder is heated from room temperature to a first platform temperature at a first heating rate, held at the first platform temperature for a period of time, and then heated from the first platform temperature to a second platform temperature at a second heating rate, held at the second platform temperature for a period of time. The first heating rate is greater than the second heating rate. Step S2.2: Cool down from the second platform temperature to the third platform temperature at the first cooling rate, and maintain the temperature at the third platform temperature for a period of time. The temperature was then lowered from the third platform to room temperature to obtain a porous lithium-rich manganese-based cathode material.

2. The method for preparing porous lithium-rich manganese-based cathode material according to claim 1, characterized in that, In step S1: During the mixing process, the speed of the mixer is set to 10 rpm / min-50 rpm / min, and the mixing time is 10 h-25 h.

3. The method for preparing porous lithium-rich manganese-based cathode material according to claim 1, characterized in that, In step S1: The lithium salt used is one or more of lithium hydroxide, lithium carbonate, and lithium chloride.

4. The method for preparing porous lithium-rich manganese-based cathode material according to claim 1, characterized in that, In step S1: The nickel manganese hydroxide precursor and lithium salt are mixed in a molar ratio of 1:1.1 to 1:1.5, wherein the lithium salt is added in excess by 5% to 25%.

5. The method for preparing porous lithium-rich manganese-based cathode material according to claim 1, characterized in that, In step S2.1: The first heating rate is set to a range of 5℃ / min-10℃ / min, the first platform temperature is set to a range of 300℃-500℃, and the holding time at the first platform temperature is set to a range of 5h-10h.

6. The method for preparing porous lithium-rich manganese-based cathode material according to claim 1, characterized in that, In step S2.1: The second heating rate is set to a range of 1℃ / min-5℃ / min, the second platform temperature is set to a range of 900℃-1100℃, and the holding time at the second platform temperature is set to a range of 10h-20h.

7. The method for preparing porous lithium-rich manganese-based cathode material according to claim 1, characterized in that, In step S2.2: The first cooling rate is set to a range of 2℃ / min-10℃ / min, the third platform temperature is set to a range of 300℃-500℃, and the holding time at the third platform temperature is set to 5h-10h.

8. The porous lithium-rich manganese-based cathode material prepared by the method according to any one of claims 1-7, having the chemical formula Li x Ni y Mn z O2, where, 1.1≤x≤1.3, 0.2≤y≤0.5, 0.4≤z≤0.

7.

9. The porous lithium-rich manganese-based cathode material according to claim 8, comprising secondary particles formed by stacking elongated, sheet-like primary particles, wherein the particle size of the primary particles ranges from 0.1 to 1.5 μm, the particle size of the secondary particles ranges from 2 to 10 μm, the pore size of the porous structure inside the secondary particles ranges from 0.5 to 3 μm, and the particle size ratio of the secondary particles to the primary particles ranges from 1.4 to 5.

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