Lithium-rich manganese-based positive electrode material based on topography design, preparation method thereof, lithium ion battery positive electrode sheet and lithium ion battery

Abstract

The application relates to the technical field of lithium batteries, and discloses a lithium-rich manganese-based positive electrode material based on morphology design, a preparation method of the lithium-rich manganese-based positive electrode material, a lithium ion battery positive electrode sheet and a lithium ion battery. The positive electrode material contains lithium and manganese, the positive electrode material contains a layered phase and a lithium-rich phase, the positive electrode material comprises a plurality of secondary particles, and the secondary particles are formed by mutual agglomeration of a plurality of primary particles. The positive electrode material provided by the application has excellent structural stability and no cracks in the crystal, and the lithium ion battery prepared from the positive electrode material has excellent volume specific capacity and cycle stability. The preparation method of the positive electrode material provided by the application controls the molar ratio of a lithium source and a precursor and sintering conditions, so as to affect the structure and performance of the positive electrode material. The preparation method is simple, safe, low in cost, has good continuity, and is suitable for mass production.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a lithium-rich manganese-based cathode material based on morphology design and its preparation method, a lithium-ion battery cathode sheet, and a lithium-ion battery. Background Technology

[0002] Traditional polycrystalline (PC) lithium-rich manganese-based layered cathode materials (LMR) are considered strong contenders for next-generation high-energy-density lithium-ion battery cathode materials due to their high discharge specific capacity (>260 mAh / g). However, the numerous intrinsic defects currently existing in lithium-rich manganese-based cathode materials hinder their widespread commercial application. These defects include, but are not limited to, low cell density due to the presence of the Li₂MnO₃ phase, resulting in low volumetric energy density; poor kinetic performance; severe voltage drop due to the phase transition from layered to spinel phase; and the formation of intercrystalline microcracks. Single-crystal SC-LMR cathode materials have attracted widespread attention. SC-LMR materials have dispersed micron-sized primary particles, which greatly reduces the specific surface area of ​​LMR materials. This is beneficial for suppressing the performance degradation caused by the infiltration of electrolyte into the bulk phase of the material. Secondly, the dispersed primary particles effectively alleviate the anisotropic volumetric deformation caused by agglomerated primary particles, thereby reducing the risk of microcrack formation. Furthermore, due to the reduction in specific surface area and the reduction in ineffective pores between particles, the compaction density of the material is greatly improved, thereby increasing the volumetric energy density of LMR materials.

[0003] However, SC-LMR materials still have unavoidable drawbacks, such as: the increased particle size further prolongs the Li chromatographic degradation process. + The diffusion distance, coupled with the already poor kinetics of LMR, further exacerbates the degradation of Li. + The diffusion properties of the Li are limited, thus inhibiting its capacity. Simultaneously, because the bond energy of Mn-O bonds is much higher than that of Ni / Co-O bonds, and the presence of more Mn-O bonds in LMR materials makes the SC morphology difficult to synthesize, often requiring higher synthesis temperatures or more complex synthesis methods to provide higher energy. The higher energy during the synthesis stage leads to the degradation of Li... + / Ni 2+ The exacerbation of the mixing phenomenon in Ni within the Li layer 2+ This further hindered Li + The spread of this will lead to Li + The generation of concentration gradients deteriorates the structural stability of the material in subsequent cycles, leading to performance degradation.

[0004] CN117747806A discloses a lithium-rich manganese-based cathode material, its precursor, preparation method, lithium-ion battery, and related electrical equipment. The precursor is prepared via a solution co-precipitation method, followed by pre-sintering to obtain oxide particles with smaller primary particle size and more interparticle gaps, which is beneficial for subsequent sintering of Li... + The diffusion of lithium hydroxide during subsequent high-temperature sintering is faster, and the decomposition temperature of lithium hydroxide is even lower, allowing for more rapid decomposition into Li. + This allows for earlier penetration into the secondary particles, altering grain boundaries and structure, and increasing charging capacity. However, because the primary particles are smaller and have more gaps, the material has a larger specific surface area, making it difficult to improve compaction density. Therefore, it does not improve volumetric energy density. Furthermore, the particles are more susceptible to electrolyte infiltration during subsequent battery cycles, leading to particle cracking and capacity decay.

[0005] Therefore, there is an urgent need to develop a cathode material, and lithium-ion batteries made from cathode materials that exhibit excellent performance in terms of volumetric capacity and cycle stability. Summary of the Invention

[0006] The purpose of this invention is to overcome the structural defects of existing lithium-rich manganese-based cathode materials, which lead to low volumetric capacity and poor cycle stability in lithium-ion batteries. This invention provides a lithium-rich manganese-based cathode material based on morphology design, its preparation method, a lithium-ion battery cathode sheet, and a lithium-ion battery.

[0007] To achieve the above objectives, the first aspect of the present invention provides a lithium-rich manganese-based cathode material, wherein the cathode material contains lithium and manganese, the cathode material contains a layered phase and a lithium-rich phase, and the cathode material includes a plurality of secondary particles, the secondary particles being formed by the aggregation of a plurality of primary particles.

[0008] A second aspect of the present invention provides a method for preparing a lithium-rich manganese-based cathode material, wherein the method includes:

[0009] The lithium source and precursor are mixed and sintered to obtain the cathode material;

[0010] The molar ratio of the lithium source to the precursor is (1.55-1.75):1;

[0011] The sintering process includes: heating from room temperature to 500-650℃ at a heating rate of 3-7℃ / min, pre-sintering for 2-8 hours, then heating to 920-980℃ at a heating rate of 3-7℃ / min, and sintering for 8-14 hours.

[0012] A third aspect of the present invention provides a lithium-rich manganese-based cathode material prepared by the above-described preparation method.

[0013] A fourth aspect of the present invention provides a lithium-ion battery positive electrode sheet, wherein the lithium-ion battery positive electrode sheet comprises the above-mentioned lithium-rich manganese-based positive electrode material.

[0014] A fifth aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising the above-described lithium-ion battery positive electrode sheet.

[0015] Through the above technical solution, the technical solution provided by the present invention achieves the following beneficial effects:

[0016] (1) The cathode material provided by the present invention contains lithium and manganese, the cathode material contains a layered phase and a lithium-rich phase, the cathode material includes multiple secondary particles, the secondary particles are formed by the aggregation of multiple primary particles, so that the cathode material has excellent structural stability and no cracks in the crystal, and the lithium-ion battery made from the cathode material has excellent volumetric capacity and cycle stability.

[0017] (2) The method for preparing the cathode material provided by this invention affects the structure and performance of the cathode material by controlling the molar ratio of lithium source to precursor and sintering conditions. This preparation method is simple, safe, low-cost, and has good continuity, making it suitable for mass production. Attached Figure Description

[0018] Figure 1 These are SEM images of the cathode materials prepared in Example 1, Comparative Examples 4 and 5;

[0019] Figure 2 This is a schematic diagram of the first charge-discharge curves of the cathode materials prepared in Example 1, Comparative Examples 4 and 5;

[0020] Figure 3 This is a schematic diagram of the discharge specific capacity curves of the cathode materials prepared in Example 1, Comparative Example 4, and Comparative Example 5 at different current rates;

[0021] Figure 4 This is a schematic diagram of the 100-cycle cycle retention rate curves of the cathode materials prepared in Example 1, Comparative Examples 4 and 5;

[0022] Figure 5 These are XRD schematic diagrams of the cathode materials prepared in Example 1 and Comparative Example 3;

[0023] Figure 6 This is a SEM image of the cathode materials prepared in Example 1, Comparative Examples 4 and 5 after 100 cycles. Detailed Implementation

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] The first aspect of the present invention provides a lithium-rich manganese-based cathode material, wherein the cathode material contains lithium and manganese, and the cathode material contains a layered phase and a lithium-rich phase; the cathode material includes a plurality of secondary particles, wherein the secondary particles are formed by the aggregation of a plurality of primary particles.

[0026] In this invention, the XRD spectra of the cathode materials prepared by Example 1 and Comparative Example 3 are shown. Figure 5 It is known that the cathode material contains a layered phase and a lithium-rich phase. In the XRD pattern of the cathode material, diffraction peaks are observed at 2θ values ​​of 17°-18°, 36°-37°, 43°-45°, 48°-49°, 58°-59°, 64°-65°, 65°-66°, and 68°-69°, indicating the presence of a layered phase. Diffraction peaks are also observed at 2θ values ​​of 20°-25°, indicating the presence of a lithium-rich phase. The XRD pattern of the cathode material provided by this invention also shows that the cathode material does not contain other crystalline structures (no other diffraction peaks). However, if the cathode material contains other crystalline structures, such as the formation of a rock salt phase, the presence of Li in the rock salt phase would be problematic. + The diffusion sites are occupied by transition metals, which hinders Li during cycling. + The diffusion of [something] causes the electrochemical performance to degrade.

[0027] In this invention, the cathode material crystal is free of cracks (as observed by SEM morphology). However, if the cathode material crystal has cracks, the cracks will cause the electrolyte to seep into the bulk phase, undergo further side reactions with the bulk material, and corrode the cathode material, resulting in battery capacity decay.

[0028] According to the present invention, the cathode material has a chemical composition expressed by the following general formula: xLi₂MnO₃·(1-x)LiMO₂, wherein M is at least one of Ni, Co, and Mn, and 0 <x<1。

[0029] According to the present invention, the compaction density of the lithium-rich manganese-based cathode material is 3-4 g / cm³. 3 The preferred concentration is 3.2-3.5 g / cm³. 3 .

[0030] In this invention, when the compaction density of the lithium-rich manganese-based cathode material does not meet the above-mentioned range, the compaction density is less than 3 g / cm³.3 At this time, there are pores between the active material particles and the conductive agent particles, which is not conducive to the conduction of ions and electrons; the compaction density is greater than 4 g / cm³. 3 At this time, the positive electrode material will crack due to excessive rolling, which is not good for the battery cycle performance.

[0031] In this invention, the positive electrode material is a solid, and its solid form is particles, preferably irregular particles. These particles have a secondary particle structure formed by the aggregation of multiple primary particles, such as... Figure 1 As shown in (a) above. The primary particles are composite oxides containing lithium and manganese, and the secondary particles are also composite oxides containing lithium and manganese. The primary particles have a strip-like morphology, and then multiple primary particles aggregate together, such as by tenon-and-mortise connections, to form the secondary particles, which have an irregular morphology.

[0032] According to the present invention, the primary particles have a strip-shaped morphology.

[0033] According to the present invention, the average length of the primary particles is 1-4 μm, preferably 2.5-3 μm.

[0034] According to the present invention, the average width of the primary particles is 0.4-0.8 μm, preferably 0.5-0.7 μm.

[0035] According to the present invention, the average aspect ratio of the primary particles is 5-6, preferably 5.2-5.8.

[0036] In this invention, the primary particles have a strip-like morphology, which then coalesce to form secondary particles with irregular shapes, thereby creating a cathode material that provides improved performance. Furthermore, by limiting the average length, average width, and average aspect ratio of the primary particles to meet the aforementioned ranges, firstly, the specific surface area of ​​the cathode material is reduced, and the structure is stable, which helps to suppress performance degradation caused by the infiltration of electrolyte into the bulk phase of the cathode material; secondly, the dispersed primary particles effectively alleviate the anisotropic volumetric deformation generated between agglomerated primary particles and maintain structural stability, thereby reducing the risk of microcrack formation; finally, due to the reduction in specific surface area and the decrease in ineffective porosity between particles, the compaction density of the cathode material is greatly improved, thereby increasing the volumetric energy density of the cathode material.

[0037] In this invention, the average length and width of the primary particles were measured using a Hitachi S-4800 scanning electron microscope.

[0038] According to the present invention, the average particle size of the secondary particles is 4-7 μm, preferably 5-6 μm.

[0039] In this invention, the average particle size of the secondary particles is measured using a laser particle size analyzer.

[0040] In a preferred embodiment of the present invention, the cathode material contains lithium and manganese, the cathode material is a layered phase and a lithium-rich phase, and the cathode material includes a plurality of secondary particles, which are formed by the aggregation of a plurality of primary particles.

[0041] The compaction density of the positive electrode material is 3.3-3.4 g / cm³. 3 ;

[0042] The average particle size of the primary particles is 2.7-2.8 μm.

[0043] A second aspect of the present invention provides a method for preparing a lithium-rich manganese-based cathode material, wherein the method includes:

[0044] The lithium source and precursor are mixed and sintered to obtain the cathode material;

[0045] The molar ratio of the lithium source to the precursor is (1.55-1.75):1;

[0046] The sintering process includes: heating from room temperature to 500-650℃ at a heating rate of 3-7℃ / min, pre-sintering for 2-8 hours, then heating to 920-980℃ at a heating rate of 3-7℃ / min, and sintering for 8-14 hours.

[0047] In this invention, when the molar ratio of the lithium source to the precursor and the sintering conditions meet the above-mentioned ranges, the cathode material can have a better morphology and structural integrity, contain a layered phase and a lithium-rich phase, and contain no other impurity phases, thus enabling the battery to have excellent electrochemical performance.

[0048] According to the present invention, the room temperature is 25-35°C.

[0049] Furthermore, the molar ratio of the lithium source to the precursor is (1.6-1.7):1.

[0050] Furthermore, the temperature is increased from room temperature to 550-620℃ at a heating rate of 4-6℃ / min, and pre-sintered for 3-7 hours. Then, the temperature is increased to 940-960℃ at a heating rate of 4-6℃ / min, and sintered for 10-12 hours.

[0051] According to the present invention, the lithium source is selected from LiOH and / or Li2CO3.

[0052] According to the present invention, the precursor is selected from Ni 0.19 Co 0.1 Mn 0.675 (OH)2, Ni 0.25 Mn0.75 (OH)2, Ni 0.2 Co 0.1 Mn 0.7 (OH)2 and Ni 0.1625 Co 0.1625 Mn 0.675 At least one of (OH)2.

[0053] According to the present invention, the mixing conditions include: a rotation speed of 1300-1700 rpm and a time of 3-7 min.

[0054] Furthermore, the mixing conditions include: a rotation speed of 1400-1600 rpm and a mixing time of 4-6 min.

[0055] A third aspect of the present invention provides a lithium-rich manganese-based cathode material prepared by the above-described preparation method.

[0056] A fourth aspect of the present invention provides a lithium-ion battery positive electrode sheet, wherein the lithium-ion battery positive electrode sheet comprises the above-mentioned lithium-rich manganese-based positive electrode material.

[0057] According to the present invention, a method for preparing a lithium-ion battery positive electrode includes the following steps:

[0058] Weigh out the positive electrode material, conductive agent (Super P / acetylene black), and binder (PVDF-polyvinylidene fluoride) in a mass ratio of 8:1:1, mix them evenly, add an appropriate amount of NMP as a dispersant to form a slurry, coat it on aluminum foil, dry it, cut it into sheets, and make lithium-ion battery positive electrode sheets.

[0059] A fifth aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising the above-described lithium-ion battery positive electrode sheet.

[0060] According to the present invention, a method for preparing a lithium-ion battery includes the following steps:

[0061] A button cell battery is assembled in an argon-atmosphere glove box using a lithium-ion battery positive electrode sheet containing positive electrode material, a lithium metal sheet as the negative electrode, a Celgard2500 separator, and an electrolyte mainly composed of 1 mol / L LiPF6 as the solute and a mixture of dimethyl carbonate, diethyl carbonate, and ethylene carbonate in a volume ratio of 1:1:1 as the solvent.

[0062] The present invention will be described in detail below through embodiments. In the following embodiments,

[0063] The morphology of the cathode material was measured using a Hitachi S-4800 scanning electron microscope;

[0064] XRD: Obtained using Rigaku's D / MAX-2500 / pc tester;

[0065] The battery volumetric capacity and cycle performance were measured using the LAND CT 2001A test system from Wuhan Landian Electronics Co., Ltd.

[0066] All raw materials used in the examples and comparative examples are commercially available products.

[0067] Example 1

[0068] LiOH and Ni in a molar ratio of 1.65:1 0.19 Co 0.1 Mn 0.675 (OH)2 was mixed at 1500 rpm for 5 min, and then the temperature was increased from 30℃ to 550℃ at a rate of 5℃ / min. After pre-sintering for 5 h, the temperature was increased to 950℃ at a rate of 5℃ / min and sintered for 12 h to obtain the cathode material (KML)A1.

[0069] Example 2

[0070] Li₂CO₃ and Ni in a molar ratio of 1.6:1 0.2 Co 0.1 Mn 0.7 (OH)2 was mixed at 1600 rpm for 6 min, and then the temperature was increased from 35℃ to 620℃ at a rate of 6℃ / min. After pre-sintering for 4 h, the temperature was increased to 960℃ at a rate of 6℃ / min and sintered for 10 h to obtain the cathode material (KML)A2.

[0071] Example 3

[0072] LiOH and Ni in a molar ratio of 1.7:1 0.1625 Co 0.1625 Mn 0.675 (OH)2 was mixed at 1400 rpm for 4 min, and then the temperature was increased from 25℃ to 550℃ at a rate of 4℃ / min. After pre-sintering for 4 h, the temperature was increased to 940℃ at a rate of 4℃ / min and sintered for 13 h to obtain the cathode material (KML)A3.

[0073] Comparative Example 1

[0074] The cathode material was prepared according to the method of Example 1, except that the heating rate was 10℃ / min, and cathode material (KML)D1 was obtained.

[0075] Comparative Example 2

[0076] The cathode material was prepared according to the method in Example 1, except that the heating rate was 15°C / min, and the cathode material (KML)D2 was obtained.

[0077] Comparative Example 3

[0078] The cathode material was prepared according to the method in Example 1, except that the molar ratio of lithium source to precursor was 1.4:1 and the heating rate was 15℃ / min, resulting in cathode material (KML)D3.

[0079] Comparative Example 4

[0080] Li₂CO₃ and Ni in a molar ratio of 0.79:1 0.19 Co 0.1 Mn 0.675 CO3 was mixed at 1600 rpm for 6 min, and then the temperature was increased from 35℃ to 450℃ at a rate of 5℃ / min. After pre-sintering for 5 h, the temperature was increased to 900℃ at a rate of 5℃ / min and sintered for 12 h to obtain the cathode material (PC)D4.

[0081] Comparative Example 5

[0082] (1) Take LiOH and Ni in a molar ratio of 1.65:1. 0.25 Mn 0.75 (OH)2, first mix half of the LiOH with Ni 0.25 Mn 0.75 (OH)2 was mixed at 1500 rpm for 5 min, and then the temperature was increased from 30℃ to 600℃ at a heating rate of 5℃ / min. After pre-sintering for 5 h, the temperature was increased to 935℃ at a heating rate of 5℃ / min and sintered for 5 h to obtain intermediate powder particles.

[0083] (2) The remaining half of the LiOH and the intermediate powder particles were mixed at a speed of 1500 rpm for 5 min. The temperature was increased from 30℃ to 600℃ at a heating rate of 5℃ / min. After pre-sintering for 5 h, the temperature was increased to 950℃ at a heating rate of 5℃ / min and sintered for 12 h to obtain the cathode material (SC)D5.

[0084] Test Example 1

[0085] The physical properties of the cathode material in the above embodiments were tested.

[0086] The compaction density of the cathode material was measured using a micrometer.

[0087] The average particle size of the primary particles was measured using a laser particle size analyzer; the results are detailed in Table 1.

[0088] Table 1. Detection results of cathode material characteristics

[0089]

[0090] Table 1 (continued)

[0091]

[0092] Test Example 2

[0093] The electrochemical performance of the cathode materials (A1-A3 and D1-D5) prepared in Example 13 and Comparative Examples 1-5 was tested, and the results are detailed in Table 2.

[0094] Assemble lithium-ion batteries:

[0095] (1) Weigh the positive electrode material (A1-A3 and D1-D5), conductive agent (Super P / acetylene black), and binder (PVDF-polyvinylidene fluoride) according to a mass ratio of 8:1:1, mix them evenly, add an appropriate amount of NMP as a dispersant to form a slurry, coat it on aluminum foil, dry it, cut it into sheets, and make lithium-ion battery positive electrode sheets.

[0096] (2) A lithium-ion battery positive electrode sheet including positive electrode material is used, a lithium metal sheet is used as the negative electrode, the separator is Celgard2500, and the main components of the electrolyte are 1 mol / L LiPF6 as solute and a mixture of dimethyl carbonate, diethyl carbonate and ethylene carbonate in a volume ratio of 1:1:1 as solvent. The cells are assembled into button cells (A1-A3 and D1-D5) in an argon atmosphere glove box.

[0097] The constant current charge-discharge test of the battery was conducted using the Landian Test System (CT2001A LAND) from Wuhan Landian Electronics Co., Ltd., and the test method is as follows:

[0098] The test was conducted in a 30°C constant temperature chamber, and the charge and discharge tests were performed at a current rate of 0.1C (1C = 250mA) and a voltage range of 2-4.8V.

[0099] Data chart analysis:

[0100] Figure 1 These are SEM images of the cathode materials prepared in Example 1, Comparative Examples 4 and 5. Figure 1 It can be seen that, Figure 1 Figure (a) is a SEM schematic diagram of the cathode material prepared in Example 1. It can be seen that the primary particles are elongated and the primary particles are connected to each other in a tenon-and-mortise manner to form secondary particles. Figure 1 Figure (b) in the figure is a schematic SEM image of the cathode material prepared in Comparative Example 4. It can be seen that the primary particles agglomerate into spherical secondary particles. Figure 1 Figure (c) in the figure is a SEM schematic diagram of the cathode material prepared in Comparative Example 5. It can be seen that the primary particles are independently dispersed and spherical, without agglomerating into secondary particles, which is called "single crystal".

[0101] Figure 2 This is a schematic diagram of the first charge-discharge curves of the cathode materials prepared in Example 1, Comparative Examples 4 and 5. Figure 2 It can be seen that the volumetric capacity of Example 1 is 886.6 mAh / cm³. 3 Comparative Example 4, due to its smaller primary particles, produced many pores, resulting in a lower compaction density and a volumetric capacity of 702.4 mAh / cm³. 3 Comparative Example 5, due to its larger grain size and structural instability, experienced a decline in electrochemical performance, with a volumetric capacity of 600.3 mAh / cm³. 3 .

[0102] Figure 3 This is a schematic diagram of the discharge specific capacity curves of the cathode materials prepared in Example 1, Comparative Examples 4 and 5 at different current rates. Figure 3 It can be seen that at relatively low current rates (0.1C-1C), the cathode material prepared in Example 1 with micron-sized primary particles and the cathode material prepared in Comparative Example 4 with nano-sized primary particles have similar discharge specific capacities. However, at higher current rates (2C, 5C), the electrochemical performance of Example 1 is superior to that of Comparative Example 1. Comparative Example 5, on the other hand, exhibits poor electrochemical performance at all current rates from low to high, demonstrating that its large particle size and unstable structure affect its electrochemical performance.

[0103] Figure 4 This is a schematic diagram of the 100-cycle retention rate curves of the cathode materials prepared in Example 1, Comparative Examples 4 and 5. Figure 4 It can be seen that the cathode materials prepared in Example 1 and Comparative Example 2, which have micron-sized primary particles, have excellent cycle stability, while the cathode material prepared in Comparative Example 4 shows obvious capacity decay. This is because the small size of the primary particles leads to an increase in ineffective pores between materials. During cycling, the electrolyte will erode into the bulk phase of the material along these pores, resulting in side reactions and other adverse effects on cycle stability. Secondly, during the lithium insertion and extraction process, the small size of the primary particles will cause anisotropic volume deformation. The continuous accumulation of this anisotropic deformation leads to stress gradients between materials, which poses a risk of cracking.

[0104] Figure 5 These are XRD patterns of the cathode materials prepared in Example 1 and Comparative Example 3. Figure 5It can be seen that in the XRD pattern of the cathode material prepared in Example 1, diffraction peaks exist at 2θ of 17°-18°, 36°-37°, 43°-45°, 48°-49°, 58°-59°, 64°-65°, 65°-66°, and 68°-69°, indicating a layered phase; in the XRD pattern of the cathode material, diffraction peaks exist at 2θ of 20°-25°, indicating a lithium-rich phase; the cathode material prepared in Example 1 does not contain other crystalline structures, while the cathode material prepared by rapid heating in Comparative Example 3 contains other crystalline structures, such as the formation of a rock salt phase, due to the presence of Li in the rock salt phase. + The diffusion sites are occupied by transition metals, which hinders Li during cycling. + The diffusion of [something] leads to a decline in electrochemical performance.

[0105] Figure 6 These are SEM images of the cathode materials prepared in Example 1, Comparative Examples 4 and 5 after 100 cycles. Figure 6 It can be seen that, Figure 6 Figure (a) is a SEM image of the cathode material prepared in Example 1 after 100 cycles. It can be seen that no cracks were generated after 100 cycles. Figure 6 Figure (b) in the figure is a SEM image of the cathode material prepared in Comparative Example 4 after 100 cycles. It can be seen that obvious intergranular cracks were generated in the secondary particles, and intragranular cracks and crystal plane slip were also generated in the primary particles. Figure 6 Figure (c) in the figure is a SEM image of the cathode material prepared in Comparative Example 5 after 100 cycles, which shows that intracrystalline cracks were generated.

[0106] Table 2 Electrochemical performance test results

[0107]

[0108] pass Figure 1-5 As can be seen from the results in Tables 1-2, the lithium-ion batteries prepared in Examples 1-3 of this invention exhibit excellent electrochemical performance, with a first-cycle discharge specific capacity as high as 253.3 mAh / g, a first-cycle coulombic efficiency of 75.3%, and a first-cycle volumetric specific capacity as high as 886.6 mAh / cm³. 3 .

[0109] Compared to Examples 1-3, Comparative Examples 1-2 used heating rates of 10°C / min and 15°C / min, respectively. The cathode materials obtained through rapid heating contained other crystalline structures, such as the formation of a rock salt phase. This is because the Li in the rock salt phase... + The diffusion sites are occupied by transition metals, which hinders Li during cycling. + The diffusion of [something] leads to a decline in electrochemical performance.

[0110] Compared to Examples 1-3, the molar ratio of lithium source to precursor in Comparative Example 3 was 1.4:1, and the heating rate was 15℃ / min. This resulted in poor morphology and low structural integrity of the cathode material, containing not only layered and lithium-rich phases but also other impurity phases—rock salt phases. Due to the presence of Li in the rock salt phase... + The diffusion sites are occupied by transition metals, which hinders Li during cycling. + The diffusion of [something] reduces the electrochemical performance of the battery.

[0111] Compared to Examples 1-3, in Comparative Example 4, the temperature was first raised to 450°C and then to 900°C to obtain the cathode material (PC). Because the primary particles were too small, the number of ineffective pores between the materials increased. During cycling, the electrolyte would erode into the bulk phase of the material along these pores, leading to side reactions and other issues that were detrimental to cycle stability. Secondly, during the lithium insertion / extraction process, the small primary particles would cause anisotropic volumetric deformation. The continuous accumulation of this anisotropic deformation would lead to stress gradients between the materials, thus posing a risk of cracking and reducing the electrochemical performance of the battery.

[0112] Compared with Examples 1-3, the cathode material (SC) prepared by Comparative Example 5 using a different preparation method has unstable structure and reduced electrochemical performance of the battery because the primary particles are independently dispersed and spherical, and do not agglomerate into secondary particles.

[0113] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A lithium-rich manganese-based cathode material, characterized in that, The cathode material contains lithium and manganese, and is composed of a layered phase and a lithium-rich phase. The cathode material includes multiple secondary particles, which are formed by the aggregation of multiple primary particles. The primary particles are elongated and are interconnected with each other in a tenon-and-mortise manner to form secondary particles. The method for preparing the positive electrode material includes: The lithium source and precursor are mixed and sintered to obtain the cathode material; The molar ratio of the lithium source to the precursor is (1.55-1.75):1, the lithium source is LiOH, and the precursor is selected from Ni. 0.19 Co 0.1 Mn 0.675 (OH)2, Ni 0.25 Mn 0.75 (OH)2, Ni 0.2 Co 0.1 Mn 0.7 (OH)2 and Ni 0.1625 Co 0.1625 Mn 0.675 At least one of (OH)2; The sintering process includes: heating from room temperature to 500-650℃ at a heating rate of 3-7℃ / min, pre-sintering for 2-8 hours, then heating to 920-980℃ at a heating rate of 3-7℃ / min, and sintering for 8-14 hours.

2. The cathode material according to claim 1, wherein, The cathode material has a chemical composition expressed by the following general formula: xLi₂MnO₃·(1-x)LiMO₂, where M is at least one of Ni, Co, and Mn, and 0 <x<1。 3. The cathode material according to claim 1, wherein, The compaction density of the cathode material is 3-4 g / cm³.

4. The cathode material according to claim 3, wherein, The compaction density of the cathode material is 3.2-3.5 g / cm³.

5. The cathode material according to claim 3, wherein, The average length of the primary particles is 1-4 μm.

6. The cathode material according to claim 5, wherein, The average length of the primary particles is 2.5-3 μm.

7. The cathode material according to claim 1, wherein, The average width of the primary particles is 0.4-0.8 μm.

8. The cathode material according to claim 7, wherein, The average width of the primary particles is 0.5-0.7 μm.

9. The cathode material according to claim 1, wherein, The average aspect ratio of the primary particles is 5-6.

10. The cathode material according to claim 9, wherein, The average aspect ratio of the primary particles is 5.2-5.

8.

11. The cathode material according to claim 1, wherein, The average particle size of the secondary particles is 4-7 μm.

12. The cathode material according to claim 11, wherein, The average particle size of the secondary particles is 5-6 μm.

13. A method for preparing the lithium-rich manganese-based cathode material according to any one of claims 1-12, characterized in that, The method includes: The lithium source and precursor are mixed and sintered to obtain the cathode material; The molar ratio of the lithium source to the precursor is (1.55-1.75):1, the lithium source is LiOH, and the precursor is selected from Ni. 0.19 Co 0.1 Mn 0.675 (OH)2, Ni 0.25 Mn 0.75 (OH)2, Ni 0.2 Co 0.1 Mn 0.7 (OH)2 and Ni 0.1625 Co 0.1625 Mn 0.675 At least one of (OH)2; The sintering process includes: heating from room temperature to 500-650℃ at a heating rate of 3-7℃ / min, pre-sintering for 2-8 hours, then heating to 920-980℃ at a heating rate of 3-7℃ / min, and sintering for 8-14 hours.

14. The preparation method according to claim 13, wherein, The molar ratio of the lithium source to the precursor is (1.6-1.7):

1.

15. The preparation method according to claim 13, wherein, The sintering process includes: heating from room temperature to 550-620℃ at a heating rate of 4-6℃ / min, pre-sintering for 3-7 hours, then heating to 940-960℃ at a heating rate of 4-6℃ / min, and sintering for 10-12 hours.

16. The preparation method according to claim 13, wherein, The mixing conditions include: a rotation speed of 1300-1700 rpm and a mixing time of 3-7 min.

17. The preparation method according to claim 16, wherein, The mixing conditions include: a rotation speed of 1400-1600 rpm and a mixing time of 4-6 min.

18. A lithium-rich manganese-based cathode material prepared by the preparation method according to any one of claims 13-17.

19. A positive electrode sheet for a lithium-ion battery, characterized in that, The lithium-ion battery cathode material comprises the lithium-rich manganese-based cathode material as described in any one of claims 1-12 and 18.

20. A lithium-ion battery, characterized in that, The lithium-ion battery includes the lithium-ion battery positive electrode sheet as described in claim 19.

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