Nickel-manganese spinel positive electrode material and preparation method and application thereof

Abstract

The invention discloses a nickel-manganese spinel positive electrode material and a preparation method and application thereof, the chemical formula of the nickel-manganese spinel positive electrode material provided by the invention is Li (1-x) NiyMnzM (2-y-z) O4, x is more than or equal to 0 and less than or equal to 0.05, and y < lt > is more than or equal to 0.5; 0.7, 1.3 lt, 0.7, 1.3 lt; z is less than or equal to 1.5, M comprises one or more of Co, Al, Ta, Ti, Nb, Ge, Y, Nb, W, Zr, Ce, Ca and Sr, and the nickel-manganese spinel positive electrode material has a spinel phase and does not contain a lithium-rich phase Li2MnO3. Compared with the prior art, the single-crystal nickel-manganese spinel positive electrode material is synthesized by adopting the low Li / Me mixed material, so that a lithium-rich phase Li2MnO3 can be prevented from being generated in the sintering process, the integrity of a spinel phase is ensured, a guarantee is further provided for transmission of lithium ions, and the nickel-manganese spinel positive electrode material shows excellent stability and rate capability in electrochemical charging and discharging.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and more particularly, to a nickel-manganese spinel cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] Nickel-substituted spinel LiNi 2-y-z , , z ,

[0006] Mn 1.5 O4 (LNMO) cathode material has become one of the most promising cathode materials that achieve a balance between cost and performance. As a low-nickel and cobalt-free material, the key component manganese in LNMO has a large elemental abundance in the earth's crust, with excellent economy and environmental friendliness. These factors make the manganese-based cathode material LNMO more economically green and sustainable. The most significant feature of LNMO is the utilization of the entire redox ability of nickel (Ni 2+ / 4+ ), which has a significantly high and flat voltage plateau at about 4.7V (vsLi / Li + ). Although the theoretical specific capacity of LNMO is only about 147mAh / g, due to its ultra-high working voltage, its energy density can reach 650Wh / g. While the high working voltage brings advantages, it also places higher requirements on the material structure. Currently, the prepared nickel-substituted spinel cathode materials cannot meet such high requirements. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above deficiencies of the prior art and provide a nickel-manganese spinel cathode material, a preparation method thereof, and an application thereof.

[0004] The present invention solves its technical problems by adopting the following technical solutions.

[0005] The present invention provides a nickel-manganese spinel cathode material, and the chemical formula of the nickel-manganese spinel cathode material is Li 1- x Ni y Mn z M 2-y-z O4, where 0≤x≤0.〇5, 0.5≤y<0.7, 1.3<z≤1.5, M includes one or more of Co, Al, Ta, Ti, Nb, Ge, Y, Nb, W, Zr, Ce, Ca, Sr, and the nickel-manganese spinel cathode material has a spinel phase and does not contain a lithium-rich phase Li2MnO3.

[0006] The present invention also provides a preparation method of the above nickel-manganese spinel cathode material, including the following steps: sintering a mixture of a precursor and a lithium source to obtain the nickel-manganese spinel cathode material, wherein: in the mixture, the molar ratio of lithium in the lithium source to the transition metal in the precursor, Li / Me, is (0.95 - 1.00):1.

[0007] The present invention provides a secondary battery comprising the above-mentioned nickel-manganese spinel cathode material.

[0008] The present invention has the following beneficial effects: This invention innovatively designs a micro-lithium-deficient spinel structure at the mixing end. While ensuring that the nickel-manganese spinel cathode material can exert its due capacity, it avoids the formation of a lithium-rich phase Li2MnO3 during high-temperature sintering due to excessive lithium source input. This reduces the formation of two-phase interfaces in the nickel-manganese oxide cathode material structure, reduces stress and strain during the charge-discharge reaction, improves the stability of the crystal structure, and thus significantly enhances the electrochemical performance. Attached Figure Description

[0009] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 A scanning electron microscope image of the nickel-manganese spinel cathode material prepared in Example 1; Figure 2 The XRD pattern of the nickel-manganese spinel cathode material prepared in Example 1; Figure 3 The room temperature activation charge-discharge curve of the coin cell provided in Example 1; Figure 4 This is a comparison of the high-temperature cycling performance of the coin cells provided in Example 1 and Comparative Examples 1 and 2; Figure 5 The XRD diffraction patterns of Example 1 and Comparative Examples 1 and 2 at the (020) peak position in lithium-rich Li2MnO3 are magnified for comparison. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0012] The following is a detailed description of a nickel-manganese spinel cathode material, its preparation method, and its application, provided by embodiments of the present invention.

[0013] In a first aspect, the present invention provides a nickel-manganese spinel cathode material, the chemical formula of which is Li.1-x Ni y Mn z M 2-y-z O4, where 0 ≤ x ≤ 0.05, 0.5 ≤ y < 0.7, 1.3 < z ≤ 1.5, M includes one or more of Co, Al, Ta, Ti, Nb, Ge, Y, Nb, W, Zr, Ce, Ca, Sr, and the nickel manganese spinel cathode material has a spinel phase and does not contain the lithium-rich phase Li2MnO3.

[0014] In the currently prepared nickel manganese spinel cathode material, in addition to the spinel phase, most also contain the lithium-rich phase Li2MnO3. The lithium-rich phase Li2MnO3 belongs to an electrochemically inert phase, which is difficult to activate and is prone to irreversible phase transformation at high voltages. In addition, the crystal structure of the lithium-rich phase is quite different from that of the spinel phase, which results in a large number of two-phase interfaces existing in the material. The two phases with large property differences will increase stress and strain during charge and discharge, damaging the overall structure of the material, and causing the nickel manganese spinel cathode material to fail faster and the capacity to decay rapidly during the cycle.

[0015] To overcome the above problems existing in the prior art, the present invention provides a nickel manganese spinel cathode material. Through the design of slightly lithium-deficient, it avoids the generation of the lithium-rich phase Li2MnO3 in the nickel manganese spinel cathode material, reduces stress and strain, ensures the integrity of the spinel phase, and further provides a guarantee for the transmission of lithium ions, so that the material exhibits excellent stability and rate performance in electrochemical charge and discharge.

[0016] It is worth noting that the relative contents of Ni and Mn are restricted by y and z respectively. Among them, when y = 0.5, the material maintains a typical spinel structure and the theoretical specific capacity is at a relatively high level (146.8 mAh / g); when 0.5 < y < 0.7, as y increases, the cycle stability of the material improves while the specific capacity decreases, and the cost increases with the increase of the Ni content. The appropriate ratio can be selected according to requirements; when y > 0.7, the spinel structure loses stability.

[0017] In some optional embodiments, the crystal form of the nickel manganese spinel cathode material is single crystal or pseudo single crystal.

[0018] In some optional embodiments, the nickel manganese spinel cathode material satisfies one or more of the following conditions: the surface residual alkali content is 200 - 400 ppm; the specific surface area BET is 0.3 - 0.8 m 2 / g; the particle size D50 is 4 - 7 μm; the distance ratio K90 is 0.4 - 1.2.

[0019] The residual alkali content on the surface of the nickel-manganese spinel cathode material provided above is 200~400ppm. Due to incomplete reaction between the precursor and lithium salt during sintering, and the reaction between the material surface and water and carbon dioxide in the air after sintering, residual alkali (LiOH, Li2CO3) is inevitable in the sintering product, with a content typically between 200~400ppm (or 0.02~0.04wt%). Excessive residual alkali will affect the subsequent use of the material, such as causing gelation during battery slurry preparation and generating corrosive HF during battery charging and discharging; insufficient residual alkali usually only occurs when the lithium metal ratio is too low, as mentioned above, which has an adverse effect on performance.

[0020] The specific surface area (BET) of the nickel-manganese spinel cathode material provided above is 0.3~0.8 m². 2 / g, specific surface area (BET) is a measure of the area of ​​a unit mass of material surface in contact with the electrolyte (electrochemically active surface). A large specific surface area is beneficial for rapid electrochemical reactions and improves specific capacity and rate performance, but it will aggravate surface side reactions and reduce cycle stability.

[0021] The aforementioned nickel-manganese spinel cathode material has a particle size D50 of 4~7μm and a particle size distance K90 of 0.4~1.2. D50 and K90 are dimensional parameters of secondary particles formed by the agglomeration of primary particles, primarily determined by the precursor particle size and sintering temperature, but also influenced by sintering time and lithium metal ratio. When the particle size is too small, the material's powder flowability and processability are poor; when the particle size is too large, the specific surface area is usually small, the lithium-ion / electron transport path is long, and the capacity and rate performance decrease. Small particle size distances typically correspond to lower sintering temperatures, resulting in a near-monocrystalline or polycrystalline material with a large specific surface area. In this case, the material may suffer from under-sintering. Large particle size distances typically correspond to higher sintering temperatures, resulting in a monocrystalline material with a smaller specific surface area. During sintering, primary particles fuse and grow, secondary particles adhere, and the sphericity of the secondary particles decreases, potentially leading to over-sintering. Furthermore, low sphericity may reduce the material's compaction density, thereby increasing contact resistance.

[0022] Secondly, the present invention provides a method for preparing the above-mentioned nickel-manganese spinel cathode material, comprising: sintering a mixture of a precursor and a lithium source to obtain the nickel-manganese spinel cathode material, wherein: in the mixture, the molar ratio of lithium in the lithium source to the transition metal in the precursor, Li / Me, is (0.95-1.00):1. Exemplarily, the molar ratio of lithium in the lithium source to the transition metal in the precursor, Li / Me, can be 0.95:1, 0.955:1, 0.96:1, 0.965:1, 0.97:1, 0.975:1, 0.98:1, 0.985:1, 0.99:1, 0.995:1, 1.00:1, etc.

[0023] Currently, when preparing nickel-manganese spinel cathode materials by sintering nickel-manganese precursors and lithium sources, the lithium metal ratio (Li / Me) is generally above 1.05 to reduce lithium loss and ensure more complete lithiation. During high-temperature sintering, excess Li in the lithium source reacts with Mn in the nickel-manganese precursor to form a lithium-rich phase, Li2MnO3, which is difficult to activate. The presence of the lithium-rich phase Li2MnO3 has the following two effects: First, a small amount of lithium-rich phase Li2MnO3 is an impurity phase mixed in the spinel phase, which destroys the integrity of the spinel phase and hinders lithium-ion transport during charging and discharging, mainly affecting capacity and rate performance. Second, the lithium-rich phase Li2MnO3, as an impurity phase mixed in the spinel phase, generates a large number of two-phase interfaces. Due to the large difference in properties between the two phases, a large amount of stress and strain will be generated at the two-phase interfaces, causing the material to fail faster during cycling and the capacity to decay rapidly. Therefore, suppressing the formation of impurity-rich lithium phases at high temperatures is an important means to improve the electrochemical performance of spinel lithium nickel manganese oxide cathode materials.

[0024] Based on the above ideas, this invention provides a method for preparing nickel-manganese spinel cathode materials. The method employs a low Li / Me mixing ratio to synthesize the nickel-manganese spinel cathode material. By reducing the amount of lithium source input, the formation of the lithium-rich phase Li₂MnO₃ is avoided during high-temperature sintering. The absence of the lithium-rich Li₂MnO₃ phase reduces impurities in the material, enhancing the integrity of the spinel phase and improving the material's cycle stability. Thanks to the slightly lithium-deficient lithium nickel manganese oxide cathode material design, the charge-discharge capacity of the material does not decrease after activation, and the cycle performance is significantly improved. This invention targets high-temperature sintered single-crystal nickel-manganese spinel materials; by optimizing the low-lithium ratio at the mixing stage, a nickel-manganese spinel cathode material with excellent electrochemical performance can be obtained.

[0025] It should be noted that while a low lithium metal ratio can completely eliminate the lithium-rich phase, it reduces the number of active lithium ions that can participate in electrochemical reactions and causes other inactive phases to form in the lithium-deficient areas, significantly reducing the material's initial specific capacity, cycle performance, and rate performance. Therefore, the lithium metal ratio must be limited to the range specified in this invention.

[0026] In some alternative embodiments, the molar ratio of lithium in the lithium source to the transition metal in the precursor, Li / Me, is (0.96~0.98):1.

[0027] In some alternative embodiments, the precursor has the chemical formula Ni. y Mn z M 1-y-z(OH)2, where 0.25 ≤ y < 0.35, 0.65 < z ≤ 0.75, and M includes one or more of Co, Al, Ta, Ti, Nb, Ge, Y, Nb, W, Zr, Ce, Ca, Sr; the lithium source includes one or more of lithium hydroxide monohydrate, anhydrous lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate.

[0028] In some optional embodiments, the rotation speed of the equipment during mixing of the lithium source and the precursor is set to 1000 - 3000 rpm, preferably 1500 - 2500 rpm; the running time is set to 0.5 - 10 min, preferably 2 - 5 min.

[0029] Exemplarily, the rotation speed of the equipment during mixing of the lithium source and the precursor can be 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, and any other value between 1000 - 3000 rpm, and the running time can be 0.5 min, 2.5 min, 4.5 min, 6.5 min, 8.5 min, 10 min, and any other value between 0.5 - 10 min.

[0030] In some optional embodiments, the sintering temperature is set to 920 - 1150 °C, preferably 950 - 1100 °C, the heating rate is set to 1 - 10 °C / min, preferably 3 - 5 °C / min, and the sintering time is preferably 8 - 12 h.

[0031] Exemplarily, the sintering temperature can be 920 °C, 940 °C, 960 °C, 980 °C, 1000 °C, 1020 °C, 1040 °C, 1060 °C, 1080 °C, 1100 °C, 1120 °C, 1140 °C, 1150 °C, and any other value between 920 - 1150 °C, the heating rate can be 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min, and any other value between 1 - 10 °C / min. The sintering time can be 8 h, 8.5 h, 9 h, 9.5 h, 10 h, 10.5 h, 11 h, 11.5 h, 12 h, and any other value between 8 - 12 h.

[0032] In some optional embodiments, the sintering atmosphere is one of air and oxygen, preferably air; the gas flow rate is 0.1 - 10 L / min, preferably 1 - 5 L / min.

[0033] For example, the gas flow rate is 0.1 L / min, 1 L / min, 2 L / min, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 10 L / min, and any other value between 0.1 and 10 L / min.

[0034] In some alternative embodiments, the process further includes crushing and sieving the sintered product.

[0035] In some alternative embodiments, crushing includes coarse crushing and fine crushing, wherein: a jaw crusher is selected for coarse crushing, with a jaw plate gap of 0.1-5 mm, preferably 0.5-2 mm; and an ultracentrifugal mill is selected for fine crushing, with a rotation speed of 6000-20000 rpm, preferably 12000-16000 rpm.

[0036] For example, the jaw plate gap of the jaw crusher can be any other value between 0.1 mm, 1.0 mm, 2.0 mm, 3.0 mm, 4.0 mm, 5.0 mm, and 0.1-5 mm, and the rotational speed of the ultracentrifugal grinder can be any other value between 6000 rpm, 10000 rpm, 15000 rpm, 20000 rpm, and 6000-20000 rpm.

[0037] In some alternative embodiments, sieving is performed on a vibrating sieve with a screen size of 25-63 μm, preferably 38-45 μm, and an amplitude of 0.5-2.5 mm, preferably 1-2 mm.

[0038] For example, the screen size of the vibrating screen is 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 63μm and any other value between 25-63μm, and the amplitude can be 0.5mm, 1.0mm, 1.5mm, 2.0mm, 2.5mm and any other value between 0.5 and 2.5mm.

[0039] Thirdly, the present invention provides a secondary battery comprising the aforementioned nickel-manganese spinel cathode material.

[0040] As can be seen from the above, this invention provides a lithium nickel manganese oxide cathode material, its preparation method, and its application. In the preparation of the lithium nickel manganese oxide cathode material, a low Li / Me mixing ratio is adopted, and a reasonable heating rate and sintering temperature are designed during the high-temperature sintering stage to avoid the formation of the lithium-rich phase Li2MnO3. Since the lithium-rich phase Li2MnO3 is an electrochemically inert phase, it is difficult to activate and is prone to irreversible phase transitions under high voltage. Furthermore, the crystal structure of the lithium-rich phase differs significantly from that of the spinel phase, resulting in a large number of two-phase interfaces existing in the material. The two phases with significantly different properties increase stress and strain during charge and discharge, damaging the overall structure of the material. This invention aims to suppress the formation of the lithium-rich phase Li2MnO3 during sintering, reduce stress and strain, and ensure the integrity of the spinel phase, thereby providing a guarantee for lithium-ion transport. This results in the material exhibiting excellent stability and rate performance during electrochemical charge and discharge.

[0041] The present invention will be further described below with reference to embodiments.

[0042] Example 1: Spherical nickel-manganese hydroxide and lithium carbonate were weighed separately with a Li / Me ratio of 0.98. The powder was poured into a blade mixer and milled at 2500 rpm for 1 min, repeated 4 times. The well-mixed powder was then poured into a sagger and gently shaken. The sagger containing the material was transferred to a sintering furnace, and dry air was purged for 20 min at a flow rate of 3 L / min. The furnace was then heated to 1000℃ and held for 10 h. The furnace was then cooled to room temperature, with air continuously purging throughout the sintering process. After sintering, the sagger was removed using heat-resistant gloves. The material inside the sagger was coarsely crushed in a jaw crusher and finely crushed in an ultracentrifugal mill. The crushed material was collected and sieved through a 40 μm screen in a vibrating sieve with an amplitude of 1.5 mm / g and a sieve time of 2 min. After sieving, the finished material was collected in a collection tray.

[0043] Example 2: Unlike Example 1, in step (1), the lithium metal ratio Li / Me is 0.97, and in step (2), the sintering temperature is 920°C. The rest are the same as in Example 1.

[0044] Example 3: Unlike Example 1, in step (1), the lithium metal ratio Li / Me is 0.96, and in step (2), the sintering temperature is 1150℃. The rest are the same as in Example 1.

[0045] Example 4: Unlike Example 1, in step (1), the lithium metal ratio Li / Me is 0.95, while the rest remains the same as in Example 1.

[0046] Example 5: Unlike Example 1, in step (1), the lithium metal ratio Li / Me is 1.00, while the rest remains the same as in Example 1.

[0047] Example 6: Unlike Example 1, in step (2), the sintering temperature is 950°C, while the rest remains the same as in Example 1.

[0048] Example 7: Unlike Example 1, in step (2), the sintering temperature is 970°C, while the rest remains the same as in Example 1.

[0049] Example 8: Unlike Example 1, in step (2), the sintering atmosphere used is O2, while the rest remains the same as in Example 1.

[0050] Example 9: Unlike Example 1, in step (2), the sintering time is 8 hours, while the rest is the same as in Example 1.

[0051] Example 10: Unlike Example 1, in step (2), the sintering time is 12 hours, while the rest is the same as in Example 1.

[0052] Comparative Example 1: Unlike Example 1, in step (1), the lithium metal ratio Li / Me is 0.90, while the rest remains the same as in Example 1.

[0053] Comparative Example 2: Unlike Example 1, in step (1), the lithium metal ratio Li / Me is 1.05, while the rest remains the same as in Example 1.

[0054] Comparative Example 3: Unlike Example 1, in step (2), the sintering atmosphere used is N2, while the rest remains the same as in Example 1.

[0055] Comparative Example 4: Unlike Example 1, in step (2), the sintering time is 15 hours, while the rest is the same as in Example 1.

[0056] Comparative Example 5: Unlike Example 1, in step (2), the sintering temperature is 850°C, while the rest is the same as in Example 1.

[0057] Comparative Example 6: Unlike Example 1, in step (2), the sintering temperature is 1200°C, while the rest is the same as in Example 1.

[0058] Experimental Example 1: The morphology of the product was observed using a field emission scanning electron microscope. The length L and width W of the visible primary particles were measured and counted at appropriate magnification of the micrographs (defined as: the particles are transformed into rectangles of equal area and closest shape, with the longer side being the length L and the shorter side being the width W), and the ratio L / W was calculated. Powder X-ray diffraction (PXRD) was performed on the product with an accelerating voltage of 40 kV and a current of 100 mA, a scanning speed of 5° / min, and a scanning range of 10 to 90°. The particle size distribution (D50) of the samples from each example and comparative example was measured using a Mastersizer 3000 laser particle size analyzer, and the radius K90 was calculated. The morphology characterization results and XRD patterns of Example 1 are shown below. Figure 1 , 2 As shown, the remaining characterization results are shown in Tables 1 and 2.

[0059] Table 1. Process parameters and specific surface area of ​​finished products for the examples and comparative examples.

[0060] Table 2. Morphology, particle size, and primary particle size of the final products in each embodiment and comparative example.

[0061] Experimental Example 2: The product was thoroughly mixed with PVDF binder, conductive carbon black, and N-methylpyrrolidone solvent to form a uniform slurry, which was then evenly coated onto aluminum foil. After drying, compaction, and die-cutting, the positive electrode sheet for the button cell was formed. This slurry was then assembled with lithium sheets as both positive and negative electrodes to create button cells. Testing was conducted at room temperature, with a voltage range of 3.0–4.9V. After the half-cells were allowed to stand for 12 hours, they were activated by performing three cycles at 25°C and 0.33°C. The activated half-cells were divided into two groups. The room temperature rate performance of the first group was tested, while the high-temperature cycling performance of the second group was tested. Specifically, the activated first group of half-cells underwent a stepped rate test at 1C, 2C, 3C, 5C, and 10C (at 25°C); the high-temperature cycling performance of the activated second group of half-cells was tested at 0.33°C (at 45°C, voltage range 3.0–4.9V). Example 1: The activation charge-discharge curves for the first three activations at 0.33C at 25°C are as follows. Figure 3 As shown, Figure 3The charge-discharge curves of the sample from Example 1 in the button cell test after three activation cycles are shown. The charging voltage plateau in the second cycle is generally lower than that in the first cycle, while the discharging voltage plateau is generally higher, indicating that the activation process reduces the polarization of the button cell. The charge-discharge curve of the third cycle is almost identical to that of the second cycle, indicating that the button cell has been fully activated. A comparison of the high-temperature cycling performance of Example 1 with Comparative Examples 1 and 2 is shown below. Figure 4 The remaining results are shown in Table 3.

[0062] Table 3 Electrochemical data for each example and comparative example

[0063] Experimental Example 3: A method for identifying lithium-rich phase Li₂MnO₃: Li₂MnO₃ exhibits a superstructure at the (020) characteristic peak in its XRD diffraction pattern. The intensity difference of the (020) characteristic peak revealed by XRD corresponds closely to the proportion of Li₂MnO₃ in the chemical formula. This allows for the determination of whether each sample contains a lithium-rich phase. Local magnified images of the (020) characteristic peak positions in Example 1 and Comparative Examples 1 and 2 are shown below. Figure 5 As shown.

[0064] Combining the test results in Tables 1 to 3 above and Figure 3-5 It can be seen that during the sintering process of the mixture of precursor and lithium source, when the lithium metal ratio increases from 0.90 to 1.05, the intensity of the characteristic peak of the lithium-rich phase (the content of lithium-rich impurity phase can be qualitatively characterized by the characteristic peak (020) of the lithium-rich phase in XRD) gradually increases (see...). Figure 5 (Results of Example 1, Comparative Examples 1 and 2). When the lithium metal ratio was increased to 1.05, the lithium-rich phase content in the nickel-manganese spinel cathode material was too high, and the capacity retention and high-rate performance of the nickel-manganese spinel cathode material were significantly reduced (see Table 3). Figure 4 (Results of Comparative Example 2). When the lithium metal ratio is not higher than the upper limit of the scope of this invention, the amount of active lithium ions is roughly positively correlated with the lithium metal ratio (when it is higher than the upper limit of the scope of this invention, the excess lithium ions exist in the form of residual alkali). When the lithium metal ratio is lower than 0.90, the content of active lithium ions is too low, resulting in too few lithium ions participating in the charge and discharge reaction, and may lead to partial structural deactivation, resulting in a significant reduction in initial specific capacity, capacity retention, and high-rate performance (see Table 3). Figure 4 (Results of Comparative Example 1). It can be seen that the lithium metal ratio is the main factor affecting the crystal structure (content of lithium-rich impurity phase), the amount of active lithium ions, and the residual alkali content. When the lithium metal ratio is controlled within the range required by this invention, the overall performance can be maintained at a good level.

[0065] Furthermore, when the mixture of precursor and lithium source is sintered at a relatively low sintering temperature, the nickel-manganese spinel cathode material exhibits polycrystalline or near-monocrystalline properties, with a D50 consistent with the precursor, a small K90, small primary particle size, and a large specific surface area. This results in a slight decrease in cycle and rate performance. If the sintering temperature is too low, the cycle and rate performance decrease significantly, and the initial capacity decreases slightly (see the results of Examples 2, 6, and 7 in Tables 1-3, and Comparative Example 5). After sintering at a higher temperature, the material exhibits large primary single-crystal particles, with larger D50 and K90, and a smaller specific surface area. This leads to a longer lithium-ion / electron transport path, a smaller electrochemical active surface, and a corresponding decrease in battery performance (see the results of Example 3 in Tables 1-3, and Comparative Example 6). The effect of sintering time is similar to that of sintering temperature (see the results of Examples 9 and 10 in Tables 1-3, and Comparative Example 4). Furthermore, since the average oxidation states of Ni and Mn increase from +2 to +3.5 when transforming from the precursor to nickel-manganese spinel cathode material, the sintering process must be carried out in an oxygen concentration of appropriate level to ensure good development of the spinel crystal structure and growth of primary particles. If the oxygen concentration is too high, the growth of primary particles is inhibited, resulting in reduced particle size and a slight decrease in battery performance (see the results of Example 8 in Tables 1-3); if the oxygen concentration is too low, the spinel crystal structure is not fully developed, leading to a significant decrease in performance (see the results of Comparative Example 3 in Tables 1-3).

[0066] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A nickel-manganese spinel cathode material, characterized in that, The chemical formula of the nickel-manganese spinel cathode material is Li 1- x Ni y Mn z M 2-y-z O4, where 0 ≤ x ≤ 0.05, 0.5 ≤ y < 0.7, 1.3 < z ≤ 1.5, M includes one or more of Co, Al, Ta, Ti, Nb, Ge, Y, Nb, W, Zr, Ce, Ca, Sr, and the nickel-manganese spinel cathode material has a spinel phase and does not contain the lithium-rich phase Li2MnO3.

2. The nickel-manganese spinel cathode material according to claim 1, characterized in that, The nickel-manganese spinel cathode material is a single crystal or a near-single crystal.

3. The nickel-manganese spinel cathode material according to claim 1 or 2, characterized in that, The specific surface area (BET) of the nickel-manganese spinel cathode material is 0.3~0.8 m². 2 / g; particle size D50 is 4~7μm; diameter spacing K90 is 0.4~1.

2.

4. The nickel-manganese spinel cathode material according to claim 1 or 2, characterized in that, The residual alkali content on the surface of the nickel-manganese spinel cathode material is 200~400ppm.

5. A method for preparing a nickel-manganese spinel cathode material according to any one of claims 1-4, characterized in that, It includes: The nickel-manganese spinel cathode material is prepared by sintering a mixture of precursor and lithium source, wherein the molar ratio of lithium in the lithium source to transition metal in the precursor, Li / Me, is (0.95-1.00):

1.

6. The preparation method according to claim 5, characterized in that, The molar ratio of lithium to transition metal in the precursor, Li / Me, in the lithium source is (0.96~0.98):

1.

7. The preparation method according to claim 5, characterized in that, The chemical formula of the precursor is Ni y Mn z M 1-y-z (OH)2, where 0.25 ≤ y < 0.35, 0.65 < z ≤ 0.75, and M includes one or more of Co, Al, Ta, Ti, Nb, Ge, Y, Nb, W, Zr, Ce, Ca, Sr; the lithium source includes one or more of lithium hydroxide monohydrate, anhydrous lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate; Preferably, the rotation speed of the equipment when mixing the lithium source and the precursor is set to 1000~3000 rpm, more preferably 1500~2500 rpm; the running time is set to 0.5~10 min, more preferably 2~5 min.

8. The preparation method according to claim 5, characterized in that, The sintering temperature is set to 920~1150℃, preferably 950~1100℃, the heating rate is set to 1~10℃ / min, preferably 3~5℃ / min, and the sintering time is preferably 8~12h; Preferably, the sintering atmosphere is either air or oxygen, with air being preferred; the gas flow rate is 0.1~10 L / min, preferably 1~5 L / min.

9. The preparation method according to claim 5, characterized in that, Also includes: The sintered products are crushed and sieved. Preferably, the crushing includes coarse crushing and fine crushing, wherein: a jaw crusher is selected for coarse crushing, with a jaw plate gap of 0.1-5mm, preferably 0.5-2mm; and an ultracentrifugal mill is selected for fine crushing, with a rotation speed of 6000-20000rpm, preferably 12000-16000rpm. Preferably, the sieving is performed on a vibrating sieve with a screen size of 25-63μm, preferably 38-45μm, and an amplitude of 0.5-2.5mm, preferably 1-2mm.

10. A secondary battery, characterized in that, It includes the nickel-manganese spinel cathode material according to any one of claims 1-4 or the nickel-manganese spinel cathode material prepared by any one of claims 5-9.

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