Lithium-excess and anion-cation co-doped lithium manganate positive electrode material with high cycle performance and preparation method of lithium manganate positive electrode material

Abstract

The invention discloses a lithium-excess and anion-cation co-doped lithium manganate positive electrode material with high cycle performance and a preparation method thereof, and belongs to the technical field of lithium ion battery positive electrode materials, the chemical formula of the lithium manganate positive electrode material is LiwAlxLayMn2-x-yO4-zFz, wlt; 1, 2, 0 lt; xlt; 0.05, 0 lt; yt; Yt; 0.05, 0 lt; z < = 0.02. The preparation method comprises the following steps: S1, uniformly mixing a lithium source, a manganese source, an aluminum-containing compound, a lanthanum-containing compound and a fluorine-containing compound in a high-efficiency mixer; s2, loading the mixed material into a sagger made of an aluminum oxide material, and sintering the sagger in a muffle furnace; and S3, crushing, screening and demagnetizing the sintered product to prepare the finished product lithium manganate material. The prepared lithium manganate positive electrode material with high cycle performance effectively solves the problems of unstable structure, manganese dissolution and the like of the lithium manganate positive electrode material in the charging and discharging process, and the cycle performance of the material is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery positive electrode materials, and particularly relates to a high-cycling performance lithium manganate positive electrode material with excess lithium and co-doping of anions and cations, and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are a new generation of green and environmentally friendly batteries, and their cathode materials are one of the key components in the manufacture of such batteries. Compared with other cathode materials, lithium manganese oxide (LiMn2O4) is not only low-cost and pollution-free, but also, as an important component of core energy storage technology in the wave of global energy transformation, its performance optimization and improvement has become a research hotspot. Lithium manganese oxide occupies an important position in the field of cathode materials due to its abundant resources, low cost, high safety and excellent high-current charge and discharge capabilities. However, the problem of capacity decay has always been the main bottleneck restricting its widespread application and technological progress.

[0003] The unique spinel structure of lithium manganese oxide provides a three-dimensional diffusion channel for lithium ions, allowing lithium ions to migrate efficiently and quickly during the charge and discharge process, making it very suitable for applications that require fast charge and discharge, such as electric vehicles and energy storage systems. However, this structure also brings challenges. In particular, during the discharge process, the Jahn-Teller effect occurs with the insertion and extraction of lithium ions, causing the crystal structure to distort, become unstable, and even cause structural collapse. In addition, Mn 2+ The disproportionation reaction with the electrolyte is also an important reason for the capacity decay of lithium manganese oxide. This reaction aggravates the destruction of the material structure, resulting in the loss of active materials and the decline of battery performance, especially under high temperature or harsh charging and discharging conditions, which seriously affects the cycle life of the battery. In order to alleviate these problems, researchers have explored and practiced from multiple angles. On the one hand, by improving the synthesis method and process conditions to optimize the crystal structure and morphology of lithium manganese oxide, its structural stability and cycle performance are enhanced; on the other hand, the surface coating and doping modification methods are used to improve the interfacial compatibility between lithium manganese oxide and the electrolyte, and reduce the occurrence of disproportionation reaction. At the same time, the development of new electrolytes and additives is also regarded as one of the effective strategies to improve the performance of lithium manganese oxide. Therefore, the development of a lithium manganese oxide positive electrode material with high cycle performance has become one of the important research directions in the current lithium-ion battery field. Summary of the Invention

[0004] In view of this, the present invention discloses a lithium excess and anion and cation co-doped high cycle performance lithium manganate positive electrode material and its preparation method. The present invention introduces lithium excess into the LiLiMnO3 protective layer, Al 3+ 、La 3+ Doping and F -Doping effectively solves the problems of structural instability and manganese dissolution of lithium manganese oxide positive electrode materials during the charging and discharging process, and significantly improves the cycle performance of the material.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention discloses a lithium excess and anion-cation co-doped high cycle performance lithium manganate positive electrode material, the chemical formula of the positive electrode material is Li w Al x La y Mn 2-x-y O 4-z F z , where: 0 <w<1.2,0<x<0.05,0<y<0.05,0<z≤0.02。

[0007] The present invention also provides a method for preparing the above-mentioned lithium excess and anion and cation co-doped high cycle performance lithium manganate positive electrode material, comprising the following steps:

[0008] S1. According to the formula, weigh an appropriate amount of lithium source, manganese source, aluminum compound, lanthanum compound, fluorine-containing compound, and place the above raw materials in an efficient mixer and mix thoroughly;

[0009] S2. The mixed material in step S1 is loaded into a sagger made of alumina and the sagger is placed in a muffle furnace for sintering;

[0010] S3. The sintered product of step S2 is crushed, sieved, and demagnetized to obtain a finished lithium manganate material, i.e., a lithium manganate positive electrode material with high cycle performance.

[0011] Preferably, in step S1, the lithium source is one of Li2CO3, LiOH, LiNO3, CH3COOLi or a combination thereof; the manganese source is one of Mn(CH3COO)2, Mn(NO3)2, Mn3O4 or a combination thereof; the aluminum-containing compound is Al2O3, the lanthanum-containing compound is La2O3, and the fluorine-containing compound is LiF.

[0012] Preferably, in step S1, the molar ratio of lithium to manganese in the lithium source and the manganese source is (1-1.2):2.

[0013] Preferably, in step S2, the sintering process in the muffle furnace is: starting from room temperature, first heating to 500-600°C at a rate of 2-4°C / min and keeping warm for 80-100 minutes, then heating to 750-850°C at a rate of 0.5-1.5°C / min and keeping warm for 150-200 minutes, then cooling to 200-300°C at a rate of -1°C / min, and finally naturally cooling to room temperature.

[0014] Preferably, in step S2, the sintering process in the muffle furnace is: starting from room temperature, first heating to 550°C at a rate of 3°C / min and keeping warm for 70 minutes, then heating to 800°C at a rate of 1.0°C / min and keeping warm for 150 minutes, then cooling to 250°C at a rate of -1°C / min, and finally naturally cooling to room temperature.

[0015] Preferably, in step S2, the sintering atmosphere in the muffle furnace is an air atmosphere or an oxygen atmosphere.

[0016] The present invention also provides the use of the above-mentioned lithium excess and anion and cation co-doped high cycle performance lithium manganate positive electrode material in the preparation of lithium ion batteries.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention introduces excess lithium into the original LiMn2O4 chemical formula, so that a LiLiMnO3 protective layer is formed on the outside of lithium manganate during the high-temperature solid-phase sintering process. In this protective layer, manganese mainly exists in the +4 valence state, which is higher than that of Mn. 3+ , Mn 4+ It has higher thermodynamic stability and is less susceptible to the Jahn-Teller effect. Because the manganese in the LiLiMnO3 protective layer is in a stable +4 valence state, its interaction with the electrolyte is weak and almost no disproportionation reaction occurs, which effectively reduces the possibility of manganese dissolving from the positive electrode material into the electrolyte and solves the problem of manganese dissolution. At the same time, the LiLiMnO3 protective layer acts as a physical barrier to isolate the electrolyte from direct contact with the internal LiMn2O4 material, reducing the probability of unnecessary side reactions and further protecting the internal active substances from damage. The LiLiMnO3 protective layer not only enhances the structural stability of the entire positive electrode material, but also enables the material to maintain a good lattice structure during repeated charge and discharge, reducing the problem of capacity decay due to structural changes; it also helps to improve the interfacial compatibility between the positive electrode material and the electrolyte, reduce interfacial resistance, and increase ion conduction efficiency, thereby enhancing the overall electrochemical performance of the battery.

[0019] (2) The present invention adopts Al 3+ 、La 3+ Chemically stable ions partially replace Mn 3+ The position of can effectively reduce the crystal structure distortion and instability caused by the Jahn-Teller effect. The Jahn-Teller effect is one of the main reasons for the structural instability of lithium manganese oxide during the charge and discharge process. By introducing cations with stable valence, this situation can be significantly improved, the overall structural stability of the material can be enhanced, and the cycle life and thermal stability of the battery can be improved.

[0020] (3) The present invention uses F - Replace some oxygen atoms to form F-Mn chemical bonds, F - The chemical bond formed between F and Mn is stronger than that between O and Mn, which helps to reduce the damage of crystal structure during charge and discharge. - The doping of Mn contributes to the reduction of the overall valence, making some Mn 4+ Reduced to Mn 3+ , thereby increasing the energy density or capacity of the material. Due to the strong electronegativity of fluorine, F - Doping can improve the interfacial compatibility between electrode materials and electrolytes, thereby further improving battery performance. By enhancing structural stability and improving interfacial compatibility, F - Doping can improve the cycle performance of the battery, allowing the battery to maintain good capacity and performance after multiple charge and discharge cycles.

[0021] In summary, the present invention introduces excessive lithium into the LiLiMnO3 protective layer, Al 3+ 、La 3+ Doping and F - Doping effectively solves the problems of structural instability and manganese dissolution in lithium manganese oxide positive electrode materials during the charge and discharge process, significantly improves the cycle performance, energy density and safety of the materials, and provides strong support for the development of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is an SEM image of the high cycle performance lithium manganate positive electrode material of Example 1 of the present invention;

[0023] Figure 2 This is a normal temperature cycle curve diagram of a lithium-ion battery made using the high cycle performance lithium manganate positive electrode material of Example 1 of the present invention and the lithium manganate positive electrode material of Comparative Example 1;

[0024] Figure 3 This is a first charge and discharge curve diagram of a lithium-ion battery manufactured using the high cycle performance lithium manganate positive electrode material of Example 1 of the present invention and the lithium manganate positive electrode material of Comparative Example 1. DETAILED DESCRIPTION

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0026] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0027] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0028] The present invention discloses a lithium excess and anion-cation co-doped high cycle performance lithium manganate positive electrode material, the chemical formula of the positive electrode material is Li w Al x La y Mn 2-x-y O 4-z F z , where: 0 <w<1.2,0<x<0.05,0<y<0.05,0<z≤0.02。

[0029] The present invention also provides a method for preparing the above-mentioned lithium excess and anion and cation co-doped high cycle performance lithium manganate positive electrode material, comprising the following steps:

[0030] S1. According to the formula, weigh an appropriate amount of lithium source, manganese source, aluminum compound, lanthanum compound, fluorine-containing compound, and place the above raw materials in an efficient mixer and mix thoroughly;

[0031] S2. The mixed material in step S1 is loaded into a sagger made of alumina and the sagger is placed in a muffle furnace for sintering;

[0032] S3. The sintered product of step S2 is crushed, sieved, and demagnetized to obtain a finished lithium manganate material, i.e., a lithium manganate positive electrode material with high cycle performance.

[0033] Among them, the above-mentioned lithium source is one of Li2CO3, LiOH, LiNO3, CH3COOLi or a combination thereof, the manganese source is one of Mn(CH3COO)2, Mn(NO3)2, Mn3O4 or a combination thereof, the aluminum-containing compound is Al2O3, the lanthanum-containing compound is La2O3, and the fluorine-containing compound is LiF; the molar ratio of lithium to manganese in the lithium source and the manganese source is (1~1.2):2.

[0034] The sintering process in the muffle furnace in step S2 is as follows: starting from room temperature, first heating to 500-600°C at a rate of 2-4°C / min and keeping warm for 80-100 min, then heating to 750-850°C at a rate of 0.5-1.5°C / min and keeping warm for 150-200 min, then cooling to 200-300°C at a rate of -1°C / min, and finally naturally cooling to room temperature.

[0035] The most preferred sintering process in the muffle furnace in step S2 is: starting from room temperature, first heating to 550°C at a rate of 3°C / min and keeping warm for 70 minutes, then heating to 800°C at a rate of 1.0°C / min and keeping warm for 150 minutes, then cooling to 250°C at a rate of -1°C / min, and finally cooling naturally to room temperature.

[0036] In the above step S2, the sintering atmosphere in the muffle furnace is an air atmosphere or an oxygen atmosphere.

[0037] The present invention also provides the use of the above-mentioned lithium excess and anion and cation co-doped high cycle performance lithium manganate positive electrode material in the preparation of lithium ion batteries.

[0038] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0039] Example 1

[0040] This embodiment has a high cycle performance lithium manganate positive electrode material Li 1.03 Al 0.04 La 0.04 Mn 1.92 O 3.98 F 0.02 The preparation method comprises the following steps:

[0041] S1. 964.73 g of lithium carbonate, 3801.69 g of manganese tetraoxide, 52.49 g of aluminum oxide, 167.73 g of lanthanum oxide, and 13.35 g of lithium fluoride were placed in a high-efficiency mixer and mixed at 49 Hz for 50 min.

[0042] S2. The mixed materials in step S1 are placed in an alumina sagger, and the sagger is placed in a muffle furnace and sintered according to the following process: starting from room temperature, first heat it to 550°C at a rate of 3°C / min and keep it at that temperature for 90 minutes, then heat it to 800°C at a rate of 1.0°C / min and keep it at that temperature for 150 minutes, then cool it to 250°C at a rate of -1°C / min, and finally cool it naturally to room temperature. The atmosphere in the muffle furnace is an oxygen atmosphere.

[0043] S3. The sintered product of step S2 was placed in a ball mill for crushing for 30 min, sieved through a 280-mesh sieve, and demagnetized to obtain a finished lithium manganate material Li 1.03 Al 0.04 La 0.04 Mn 1.92 O 3.98 F 0.02 .

[0044] Figure 1 The SEM image of the high cycle performance lithium manganate positive electrode material prepared in this embodiment with excess lithium and anion and cation co-doping is shown in Figure 2. Figure 1 It can be seen that the high-cycling performance lithium manganate positive electrode material with excess lithium and co-doping of anions and cations prepared in this embodiment exhibits a spherical structure, the surface of which is not smooth, but has a certain degree of roughness and a granular structure. This spherical structure helps to improve the cycling stability and electrochemical performance of the material. The spherical particles can provide more active sites, which is conducive to the insertion and extraction of lithium ions, thereby improving the capacity and cycle life of the battery.

[0045] Example 2

[0046] This embodiment has a high cycle performance lithium manganate positive electrode material Li 1.08 Al 0.04 La 0.02 Mn 1.94 O 3.99 F 0.01 The preparation method comprises the following steps:

[0047] S1. 776.1 g of lithium hydroxide, 4441.8 g of manganese tetraoxide, 61.2 g of aluminum oxide, 97.8 g of lanthanum oxide, and 7.8 g of lithium fluoride were placed in a high-efficiency mixer and mixed at 49 Hz for 60 min.

[0048] S2. The mixed materials in step S1 are placed in an alumina sagger, and the sagger is placed in a muffle furnace and sintered according to the following process: starting from room temperature, first heat it to 500°C at a rate of 2°C / min and keep it warm for 100 minutes, then heat it to 750°C at a rate of 0.5°C / min and keep it warm for 200 minutes, then cool it to 200°C at a rate of -1°C / min, and finally cool it naturally to room temperature. The atmosphere in the muffle furnace is an oxygen atmosphere.

[0049] S3. The sintered product of step S2 was placed in a ball mill for crushing for 20 min, sieved through a 250-mesh sieve, and demagnetized to obtain a finished lithium manganate material Li 1.08 Al 0.04 La 0.02 Mn 1.94 O 3.99 F 0.01 .

[0050] Example 3

[0051] This embodiment has a high cycle performance lithium manganate positive electrode material Li 0.98 Al 0.03 La 0.02 Mn 1.95 O 3.99 F 0.01 The preparation method comprises the following steps:

[0052] S1. 675.7 g of lithium nitrate, 3489.5 g of manganese nitrate, 15.3 g of aluminum oxide, 32.6 g of lanthanum oxide, and 2.6 g of lithium fluoride were placed in a high-efficiency mixer and mixed at 49 Hz for 60 min.

[0053] S2. The mixed materials in step S1 are placed in an alumina sagger, and the sagger is placed in a muffle furnace and sintered according to the following process: starting from room temperature, first heat it to 600°C at a rate of 4°C / min and keep it at that temperature for 80 minutes, then heat it to 850°C at a rate of 1.5°C / min and keep it at that temperature for 150 minutes, then cool it to 300°C at a rate of -1°C / min, and finally cool it naturally to room temperature. The atmosphere in the muffle furnace is air.

[0054] S3. The sintered product of step S2 was placed in a ball mill for crushing for 30 min, sieved through a 300-mesh sieve, and demagnetized to obtain a finished lithium manganate material Li 0.98 Al 0.03 La 0.02 Mn 1.95 O 3.99 F 0.01 .

[0055] Comparative Example 1

[0056] This embodiment is a method for preparing lithium manganese oxide LiMn2O4, a positive electrode material for lithium ion batteries, and the specific steps are as follows:

[0057] (1) 399 g of lithium carbonate and 1601 g of manganese tetraoxide were placed in a high-efficiency mixer and mixed at 49 Hz for 50 min.

[0058] (2) The mixed materials in step (1) are placed in a sagger made of alumina, and the sagger is placed in a muffle furnace and sintered according to the following process: starting from room temperature, first heating to 550°C at a rate of 3°C / min and keeping warm for 90 minutes, then heating to 800°C at a rate of 1.0°C / min and keeping warm for 150 minutes, then cooling to 250°C at a rate of -1°C / min, and finally naturally cooling to room temperature, wherein the atmosphere in the muffle furnace is an oxygen atmosphere.

[0059] (3) The sintered product of step (2) was placed in a ball mill for crushing for 30 minutes, and then sieved through a 280-mesh sieve to remove magnetism to obtain finished product lithium manganate LiMn2O4.

[0060] The lithium manganese oxide positive electrode materials prepared in Example 1 and Comparative Example 1 were made into button batteries and subjected to electrochemical performance tests. The specific analysis is as follows.

[0061] Figure 2The cycle performance curves of button-type batteries made from the lithium manganese oxide positive electrode materials prepared in Example 1 and Comparative Example 1 are shown after 33 cycles at room temperature at a current density of 1C. As can be seen from the figure, the capacity retention rate of Example 1 shows a slow downward trend with increasing cycle number. In the first few cycles, the capacity retention rate fluctuates slightly, but is generally stable. At the 33rd cycle, the capacity retention rate is 98.94%. The capacity retention rate of Comparative Example 1 shows a rapid downward trend with increasing cycle number. In the first few cycles, the capacity retention rate decreases significantly, especially after the third cycle, where the downward trend becomes more pronounced. At the 33rd cycle, the capacity retention rate is 94.8%. This demonstrates that the lithium-ion battery made from the lithium manganese oxide positive electrode material prepared in Example 1 of the present invention has better cycling stability and can maintain a high capacity during multiple charge and discharge processes, thereby extending the battery's service life.

[0062] Figure 3 The first cycle charge-discharge curves of button cells made from the lithium manganese oxide positive electrode materials prepared in Example 1 and Comparative Example 1 at a charge-discharge voltage range of 2.7V to 4.3V at a current density of 1C are shown. The figure shows that the discharge capacity of Example 1 of the present invention slowly decreases with increasing cycle number, with slight fluctuations in the capacity retention rate in the first few cycles, but is generally stable. At the 33rd cycle, the discharge capacity is 126.4 mAh / g. The discharge capacity of Comparative Example 1 decreases rapidly with increasing cycle number, significantly decreasing in the first few cycles, and the downward trend becomes more pronounced after the third cycle. At the 33rd cycle, the discharge capacity is only 118.5 mAh / g. This demonstrates that the lithium-ion battery made from the lithium manganese oxide positive electrode material prepared in Example 1 of the present invention has better cycle stability and higher discharge capacity retention rate.

[0063] The above is a detailed introduction to a lithium excess and anion and cation co-doped high cycle performance lithium manganate positive electrode material and its preparation method disclosed in the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A lithium excess and anion and cation co-doped high cycle performance lithium manganate positive electrode material, characterized in that: The chemical formula of the positive electrode material is Li w Al x La y Mn 2-x-y O 4-z F z , where: 0 <w<1.2,0<x<0.05,0<y<0.05,0<z≤0.02。 2. The method for preparing the lithium excess and anion-cation co-doped high cycle performance lithium manganate positive electrode material according to claim 1, characterized in that: The steps include: S1. According to the formula, weigh an appropriate amount of lithium source, manganese source, aluminum compound, lanthanum compound, fluorine-containing compound, and place the above raw materials in an efficient mixer and mix thoroughly; S2. The mixed material in step S1 is loaded into a sagger made of alumina and the sagger is placed in a muffle furnace for sintering; S3. The sintered product of step S2 is crushed, sieved, and demagnetized to obtain a finished lithium manganate material, i.e., a lithium manganate positive electrode material with high cycle performance.

3. The method for preparing a high cycle performance lithium manganate positive electrode material with excess lithium and anion and cation co-doping according to claim 2, characterized in that: In step S1, the lithium source is one of Li2CO3, LiOH, LiNO3, CH3COOLi or a combination thereof; the manganese source is one of Mn(CH3COO)2, Mn(NO3)2, Mn3O4 or a combination thereof; the aluminum-containing compound is Al2O3, the lanthanum-containing compound is La2O3, and the fluorine-containing compound is LiF.

4. The method for preparing a high cycle performance lithium manganate positive electrode material with excess lithium and anion and cation co-doping according to claim 3, characterized in that: In step S1, the molar ratio of lithium to manganese in the lithium source and the manganese source is (1-1.2):

2.

5. The method for preparing a high cycle performance lithium manganate positive electrode material with excess lithium and anion and cation co-doping according to claim 2, characterized in that: In step S2, the sintering process in the muffle furnace is as follows: starting from room temperature, first heating to 500-600°C at a rate of 2-4°C / min and keeping warm for 80-100 minutes, then heating to 750-850°C at a rate of 0.5-1.5°C / min and keeping warm for 150-200 minutes, then cooling to 200-300°C at a rate of -1°C / min, and finally naturally cooling to room temperature.

6. The method for preparing a high cycle performance lithium manganate positive electrode material with excess lithium and anion and cation co-doping according to claim 5, characterized in that: In step S2, the sintering process in the muffle furnace is as follows: starting from room temperature, first heating to 550°C at a rate of 3°C / min and keeping warm for 70 minutes, then heating to 800°C at a rate of 1.0°C / min and keeping warm for 150 minutes, then cooling to 250°C at a rate of -1°C / min, and finally naturally cooling to room temperature.

7. The method for preparing a high cycle performance lithium manganate positive electrode material with excess lithium and anion and cation co-doping according to claim 5, characterized in that: In step S2, the sintering atmosphere in the muffle furnace is an air atmosphere or an oxygen atmosphere.

8. Use of the lithium-excess and anion-cation co-doped high-cycling performance lithium manganate positive electrode material according to claim 1 in the preparation of lithium-ion batteries.

Images