Method for synthesizing lithium-rich manganese-based positive electrode through three-stage calcination strategy

Abstract

The invention discloses a method for synthesizing a lithium-rich manganese-based positive electrode by a three-stage calcination strategy. The method comprises the following steps: heating a mixture of a lithium-rich manganese-based positive electrode material precursor and lithium carbonate to a first temperature at a first heating rate, and carrying out heat preservation for a first time for pre-calcination; and after the pre-calcination is finished, heating to a second temperature at a first heating rate, then heating to a third temperature at a second heating rate, keeping the temperature for a second time, cooling to the second temperature at a first cooling rate, and finally cooling to the room temperature at a second cooling rate. According to the method, the formation process of the lithium-rich manganese-based positive electrode layered structure is regulated and controlled by stages through a three-stage calcination strategy, so that the formation of an ordered and stable layered structure with less lithium-nickel mixing and oxygen vacancies is facilitated, irreversible oxygen loss and structural phase change in the circulation process are inhibited, the circulation performance of an electrode material is obviously improved, and the service life of the lithium-rich manganese-based positive electrode is prolonged. And the production energy consumption is reduced by effectively shortening the constant-high-temperature calcination time.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology, specifically to a method for synthesizing lithium-rich manganese-based cathodes using a three-stage calcination strategy. Background Art

[0002] With the increasing demand for longer driving range in new energy vehicles, lithium-rich manganese-based cathode materials have become a candidate for high-energy-density power battery electrode materials due to their advantages such as high capacity and high operating voltage. However, the poor cycle performance of lithium-rich manganese-based cathode materials limits their commercial development. Poor cycle performance of cathode materials can significantly shorten the lifespan of battery packs, which can impose a significant economic burden on consumers. Therefore, developing lithium-rich manganese-based cathode materials with excellent cycle performance is of great significance for the future development of high-energy-density power batteries with stable performance and long service life.

[0003] The cycling performance of lithium-rich manganese-based cathode materials is closely related to the stability of the layered bulk structure responsible for lithium-ion diffusion. Due to irreversible oxygen loss and transition metal ion mixing, the layered structure is prone to phase transitions during cycling, leading to irreversible voltage and capacity drops. Numerous efforts have been made to overcome these problems, such as coating and heteroatom doping. However, these modification strategies primarily affect the surface and interface structures of the cathode material, with limited effect on stabilizing the bulk structure. Furthermore, the relatively complex modification processes can increase production costs.

[0004] Achieving more comprehensive and in-depth stabilization of the layered structure is one of the current efforts to improve the cycle performance of lithium-rich manganese-based cathode materials. The ordered layered structure of lithium-rich manganese-based cathode materials mainly forms in the high-temperature region, that is, after pre-calcination, the precursor and lithium salt gradually form the target layered structure through a high-temperature solid-state reaction. Traditional calcination procedures typically involve rapidly heating to a high temperature followed by prolonged holding at that temperature to obtain the target product. However, prolonged exposure of the cathode material to a constant-temperature calcination environment easily leads to the destruction of transition metal-oxygen bonds, resulting in excessive oxygen vacancies and threatening the stability of the layered structure. Therefore, developing a calcination strategy suitable for forming a more ordered and stable layered structure to achieve deep stabilization is of great significance. Summary of the Invention

[0005] In order to improve the poor cycle performance of lithium-rich manganese-based cathode materials, this invention provides a calcination method for synthesizing lithium-rich manganese-based cathode materials with excellent cycle performance in a highly efficient, controllable, and low-cost manner.

[0006] The technical solution to achieve the objective of this invention is: a method for synthesizing lithium-rich manganese-based cathodes using a three-stage calcination strategy, comprising the following steps:

[0007] (1) The mixture of lithium-rich manganese-based cathode material precursor and lithium carbonate is heated to a first temperature at a first heating rate and then held at the temperature for a first time for pre-calcination.

[0008] (2) After the precalcination is completed, the temperature is raised to the second temperature at the first heating rate, then raised to the third temperature at the second heating rate and held for a second time, then cooled to the second temperature at the first cooling rate, and finally cooled to room temperature at the second cooling rate to obtain lithium-rich manganese-based cathode material.

[0009] Preferably, the first heating rate and the second cooling rate are both 5℃ / min, the second heating rate and the first cooling rate are both 0.5℃ / min, the first temperature is 450℃, the second temperature Tcs is 775~825℃, preferably 800℃, the third temperature is 850℃, the first holding time is 6h, and the second holding time is (3.6Tcs-2220)min.

[0010] Preferably, the precursor of lithium-rich manganese-based cathode material has a composition of Mn 0.54 Co 0.13 Ni 0.13 CO3.

[0011] Preferably, the mass ratio of lithium-rich manganese-based cathode material precursor to lithium carbonate is 1:0.45.

[0012] Compared with the prior art, the positive effects of the present invention are:

[0013] (1) Compared with conventional calcination process, the three-stage calcination strategy of the present invention, which slowly raises the temperature in the high-temperature region, helps to alleviate the generation of lithium-nickel mixing during the formation of layered structure;

[0014] (2) Compared with conventional calcination procedures, the shortening of the constant high temperature calcination time in the three-stage calcination strategy of the present invention helps to alleviate the damage of transition metal-oxygen bonds caused by long-term constant high temperature, and helps to reduce the generation of excessive oxygen vacancies during the ripening process of layered structures.

[0015] (3) Compared with conventional calcination process, the slow cooling in the high temperature region in the three-stage calcination strategy of the present invention helps to release the residual stress in the layered structure during the heat treatment process and helps to stabilize the formed layered structure.

[0016] (4) This invention not only achieves efficient and controllable synthesis of ordered and stable layered structures with fewer lithium-nickel mixtures and oxygen vacancies, but also effectively reduces production energy consumption by shortening the constant high temperature calcination time, providing a reference for the commercial production of lithium-rich manganese-based cathode materials in the future. Attached Figure Description

[0017] Figure 1This is a schematic diagram of the conventional calcination procedure in the comparative example and the three-stage calcination strategy (Tcs = 725, 750, 775, 800, 825℃) in Examples 1, 2, 3, 4, and 5.

[0018] Figure 2 It is a lithium-rich manganese-based cathode precursor (Mn 0.54 Ni 0.13 Co 0.13 TG / DSC curves of a mixture of CO3 and lithium carbonate.

[0019] Figure 3 The comparison example (Tcs = 850℃) and Examples 1, 2, 3, 4, and 5 (Tcs = 725, 750, 775, 800, and 825℃) shows the presence of Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 XRD pattern of O2.

[0020] Figure 4 The electrochemical performance graphs of the cathode materials in Comparative Examples and Examples 1, 2, 3, 4, and 5 are as follows: (a) Cycling performance graphs of each sample (Tcs = 725, 750, 775, 800, 825, 850 °C) (100 cycles at 1C); (b) Long-cycle performance graphs of the samples in Comparative Example (Tcs = 850 °C) and Example 4 (Tcs = 800 °C) (200 cycles at 1C); (c) and (d) are the discharge curves of Comparative Example and Example 4 at 1C for the first, 100, 150, and 200 cycles.

[0021] Figure 5 XPS curves of samples from the comparative example (Tcs = 850℃) and Example 4 (Tcs = 800℃) after 100 cycles at 1C: (a) and (d) O 1s spectrum, (b) and (e) Mn 2p spectrum, (c) and (f) Mn content in each sample. 3+ With Mn 4+ The relative content of.

[0022] Figure 6 The following are HRTEM images of the surface and interface of lithium-rich manganese-based cathode materials after 100 cycles at 1C under different calcination procedures: (a) Comparative example (Tcs = 850℃), (b) Example 4 (Tcs = 800℃). Detailed Implementation

[0023] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0024] The inventive concept of this invention is:

[0025] (1) When the calcination temperature exceeds the melting point of lithium carbonate, the lithium salt and transition metal oxide can react more fully to form the target layered structure. However, the relatively high calcination temperature can easily cause molten lithium to impact the transition metal skeleton when entering the interlayer, which in turn leads to the generation of more lithium-nickel mixture. Therefore, we adopt a temperature control program of slow heating to make molten lithium enter the interlayer more orderly and slowly, and suppress the generation of excess lithium-nickel mixture.

[0026] (2) In the traditional calcination process, long-term constant high-temperature calcination can easily cause the destruction of transition metal-oxygen bonds, which in turn leads to the generation of excess oxygen vacancies. Therefore, we have effectively shortened the constant high-temperature calcination time, which not only inhibits the generation of excess oxygen vacancies, but also reduces production energy consumption.

[0027] (3) Rapid cooling after constant-temperature calcination in conventional calcination procedures can easily lead to the inability to release the residual internal stress in the layered structure during heat treatment, resulting in large lattice deformation during cooling. Therefore, we adopted a slow cooling method after constant-temperature calcination to slowly release the residual internal stress in the layered structure, thereby stabilizing the formed ordered layered structure. (4) In order to ensure that lithium carbonate in the molten state can fully react with the lithium-rich manganese-based precursor, the starting temperature of the three-stage calcination was set higher than the melting point of lithium carbonate (718℃). In order to explore the suitable starting temperature of the three-stage calcination strategy, we selected 5 temperature points (Tcs = 725, 750, 775, 800, 825℃) between the melting point of lithium carbonate and the highest calcination temperature. It is worth mentioning that in order to control the calcination time of conventional calcination procedures and the three-stage calcination strategy in the high-temperature region to be the same, the second holding time of the three-stage calcination strategy at the third temperature, i.e., 850℃, was set to (3.6Tcs-2220) min according to the Tcs value.

[0028] Comparative Example

[0029] Combination Figure 1 The Tcs is 850℃. In this comparative example, lithium-rich manganese-based cathode material was synthesized using a conventional calcination procedure, and was obtained through the following steps:

[0030] (1) The lithium-rich manganese-based cathode precursor (Mn 0.54 Co 0.13 Ni 0.13 A mixture of CO3 (1g, Haian Zhichuan Battery Materials Technology Co., Ltd.) and lithium carbonate (0.45g) (total 1.45g) was precalcined in a muffle furnace at a temperature of 5℃ / min to 450℃ and held for 6h.

[0031] (2) After the pre-calcination is completed, the temperature is increased to 850℃ at a rate of 5℃ / min and held for 14 hours. After the holding period, the temperature is increased to 850℃ at a rate of 5℃ / min.

[0032] The temperature was reduced to room temperature by 0.5 min to obtain lithium-rich manganese-based cathode material. The lithium-rich manganese-based cathode material synthesized under conventional calcination procedure was named with the code "Tcs=850℃".

[0033] Example 1

[0034] Combination Figure 1 The Tcs in Example 1 is 725℃. The lithium-rich manganese-based cathode material synthesized using a three-stage calcination strategy was prepared through the following steps:

[0035] (1) The lithium-rich manganese-based cathode precursor (Mn 0.54 Co 0.13 Ni 0.13 A mixture of CO3 (1g, Haian Zhichuan Battery Materials Technology Co., Ltd.) and lithium carbonate (0.45g) (total 1.45g) was precalcined in a muffle furnace at a temperature of 5℃ / min to 450℃ and held for 6h.

[0036] (2) After pre-calcination, the temperature was increased to 725°C at 5°C / min, then slowly increased to 850°C at 0.5°C / min, and then held at 850°C for 6.5 hours. After the holding period, the temperature was slowly decreased to 725°C at 0.5°C / min, and finally rapidly decreased to room temperature at 5°C / min to obtain the lithium-rich manganese-based cathode material. The lithium-rich manganese-based cathode material synthesized by the three-stage calcination strategy in this example is named with the code "Tcs=725°C".

[0037] Example 2

[0038] Combination Figure 1 The Tcs in Example 2 is 750℃. The lithium-rich manganese-based cathode material synthesized using a three-stage calcination strategy was prepared through the following steps:

[0039] (1) The lithium-rich manganese-based cathode precursor (Mn 0.54 Co 0.13 Ni 0.13 A mixture of CO3 (1g, Haian Zhichuan Battery Materials Technology Co., Ltd.) and lithium carbonate (0.45g) (total 1.45g) was precalcined in a muffle furnace at a temperature of 5℃ / min to 450℃ and held for 6h.

[0040] (2) After pre-calcination, the temperature was increased to 750°C at 5°C / min, then slowly increased to 850°C at 0.5°C / min, and then held at 850°C for 8 hours. After the holding period, the temperature was slowly decreased to 750°C at 0.5°C / min, and finally rapidly decreased to room temperature at 5°C / min to obtain the lithium-rich manganese-based cathode material. The lithium-rich manganese-based cathode material synthesized by the three-stage calcination strategy in this example is named with the code "Tcs=750°C".

[0041] Example 3

[0042] Combination Figure 1 The Tcs in Example 3 is 775℃. The lithium-rich manganese-based cathode material synthesized using a three-stage calcination strategy was prepared through the following steps:

[0043] (1) The lithium-rich manganese-based cathode precursor (Mn 0.54 Co 0.13 Ni 0.13 A mixture of CO3 (1g, Haian Zhichuan Battery Materials Technology Co., Ltd.) and lithium carbonate (0.45g) (total 1.45g) was precalcined in a muffle furnace at a temperature of 5℃ / min to 450℃ and held for 6h.

[0044] (2) After pre-calcination, the temperature was increased to 775°C at 5°C / min, then slowly increased to 850°C at 0.5°C / min, and then held at 850°C for 9.5 hours. After the holding period, the temperature was slowly decreased to 775°C at 0.5°C / min, and finally rapidly decreased to room temperature at 5°C / min to obtain the lithium-rich manganese-based cathode material. The lithium-rich manganese-based cathode material synthesized by the three-stage calcination strategy in this example is named with the code "Tcs=775°C".

[0045] Example 4

[0046] Combination Figure 1 In Example 4, the lithium-rich manganese-based cathode material synthesized using a three-stage calcination strategy with Tcs = 800℃ was obtained through the following steps:

[0047] (1) The lithium-rich manganese-based cathode precursor (Mn 0.54 Co 0.13 Ni 0.13 A mixture of CO3 (1g, Haian Zhichuan Battery Materials Technology Co., Ltd.) and lithium carbonate (0.45g) (total 1.45g) was precalcined in a muffle furnace at a temperature of 5℃ / min to 450℃ and held for 6h.

[0048] (2) After pre-calcination, the temperature was increased to 800℃ at 5℃ / min, then slowly increased to 850℃ at 0.5℃ / min, and then held at 850℃ for 11 hours. After the holding period, the temperature was slowly decreased to 800℃ at 0.5℃ / min, and finally rapidly decreased to room temperature at 5℃ / min to obtain the lithium-rich manganese-based cathode material. The lithium-rich manganese-based cathode material synthesized by the three-stage calcination strategy in this example is named with the code "Tcs=800℃".

[0049] Example 5

[0050] Combination Figure 1 The Tcs in Example 5 is 825℃. The lithium-rich manganese-based cathode material synthesized using a three-stage calcination strategy was prepared through the following steps:

[0051] (1) The lithium-rich manganese-based cathode precursor (Mn 0.54 Co 0.13 Ni 0.13 A mixture of CO3 (1g, Haian Zhichuan Battery Materials Technology Co., Ltd.) and lithium carbonate (0.45g) (total 1.45g) was precalcined in a muffle furnace at a temperature of 5℃ / min to 450℃ and held for 6h.

[0052] (2) After pre-calcination, the temperature was increased to 825°C at 5°C / min, then slowly increased to 850°C at 0.5°C / min, and then held at 850°C for 12.5 hours. After the holding period, the temperature was slowly decreased to 825°C at 0.5°C / min, and finally rapidly decreased to room temperature at 5°C / min to obtain the lithium-rich manganese-based cathode material. The lithium-rich manganese-based cathode material synthesized by the three-stage calcination strategy in this example is named with the code "Tcs=825°C".

[0053] Figure 2 It is a lithium-rich manganese-based cathode precursor (Mn 0.54 Ni 0.13 Co 0.13 TG / DSC curves of a mixture of CO3 and lithium carbonate were obtained. A significant decrease in the mass of the mixture was observed as the temperature increased from 350°C to 500°C, corresponding to the decomposition of the transition metal carbonate. As the temperature gradually increased, the mass decrease slowed, accompanied by the gradual reaction of the transition metal oxide with the lithium salt to form the target product. Notably, an endothermic peak at 719°C corresponds to the melting of lithium carbonate, indicating that the molten lithium carbonate can then react more fully with the transition metal oxide. An endothermic peak at 830°C corresponds to the completion of the ordered layered structure. An exothermic peak at 928°C corresponds to the decomposition of lithium carbonate. Based on the physicochemical changes of the precursor and lithium salt mixture during the heating process, to ensure a more complete reaction between the transition metal oxide and the lithium salt, we selected 725°C (above the melting point of lithium carbonate) as the initial calcination temperature for the three-stage calcination strategy.

[0054] Figure 3 The comparison example (Tcs = 850℃) and Examples 1, 2, 3, 4, and 5 (Tcs = 725, 750, 775, 800, and 825℃) shows the presence of Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 XRD pattern of O2. For example... Figure 3As shown, the XRD pattern of the sample synthesized by the three-stage calcination strategy corresponds to the α-NaFeO2 layered structure. In addition, the superlattice diffraction peak at 20-25° corresponds to LiMn6, which means that the three-stage calcination strategy successfully synthesized the layered structure of lithium-rich manganese-based cathode. The diffraction peak intensities of the sample synthesized by the three-stage calcination strategy are significantly improved compared to the sample synthesized by the conventional calcination procedure, which means that the crystallinity of the cathode material is significantly improved after optimization. The peak intensity ratio of diffraction peaks (003) and (104) can reflect the lithium-nickel mixture in the layered structure. After calculation, the I of the cathode material in Examples 1, 2, 3, 4, 5 (Tcs = 725, 750, 775, 800, 825℃) and the comparative example (Tcs = 850℃) is significantly improved. (003) / I (104) The values ​​were 1.44, 1.33, 1.38, 1.65, 1.54, and 1.28, respectively, indicating that the three-stage calcination strategy effectively suppressed lithium-nickel mixing. The cathode material in Example 4 (Tcs = 800℃) exhibited the lowest degree of lithium-nickel mixing. The degree of splitting of the two pairs of diffraction peaks (108) / (110) and (006) / (102) reflects the orderliness of the synthesized layered structure. Figure 3 As shown in (b), compared with the sample synthesized by the conventional calcination strategy in the comparative example, the two pairs of diffraction peaks of the cathode material synthesized by the three-stage calcination strategy in the example are more clearly split, which means that the three-stage calcination strategy helps to form a more ordered layered structure.

[0055] To investigate the impact of the above three-stage calcination strategy on the electrochemical performance of the cathode material Figure 4 (a) shows the cycling performance graphs (100 cycles at 1C) of Examples 1, 2, 3, 4, 5 and the comparative examples. As shown in the figure, the capacity retention rates of each sample (Tcs = 725, 750, 775, 800, 825, 850 °C) after 100 cycles at 1C were 81.2%, 82.7%, 86.1%, 93.6%, 89.5%, and 88.5%, respectively. Among them, the cathode material in Comparative Example 4 (Tcs = 800 °C) showed the best cycling performance, which was significantly higher than that of the cathode material synthesized by the conventional calcination process. This means that selecting an appropriate calcination start temperature to carry out a three-stage calcination strategy can significantly improve the cycling performance of the electrode material.

[0056] To further investigate the impact of the three-stage calcination strategy on the cycle performance of lithium-rich manganese-based cathode materials, we compared the cathode materials in the comparative example (Tcs = 850℃) and Example 4 (Tcs = 800℃). Figure 4 As shown in (b), the capacity retention rates of the two samples after 200 cycles at 1C were 38% and 85.2%, respectively. This indicates that the three-stage calcination strategy in Example 4 (Tcs = 800℃) significantly improved the cycling performance of the lithium-rich manganese-based cathode material. Figure 4 As shown in (c) and (d) in the example, compared with the cathode material synthesized by the conventional calcination process in the comparative example, the cathode material synthesized by the three-stage calcination strategy (Tcs = 800 °C) in Example 4 exhibits a smaller voltage drop during cycling.

[0057] Figure 5 The XPS curves of the cathode material in the comparative example and Example 4 (Tcs = 800°C) after 100 cycles at 1C are shown. Figure 5 As shown in (a) and (d), the relative content of lattice oxygen on the surface of the cathode material in Comparative Example and Example 4 (Tcs = 800 °C) after 100 cycles was 17.4% and 20.7%, respectively. This indicates that the novel calcination strategy helps to suppress irreversible oxygen loss. The lithium-rich manganese-based cathode material showed increased Mn content before and after cycling. 4+ With Mn 3+ Changes in relative content are closely related to irreversible oxygen loss from the layered structure and structural phase transitions during cycling. For example... Figure 5 As shown in (c) and (f) in the figure, after 100 cycles, the surface Mn of the cathode material synthesized by the conventional calcination process in the comparative example is... 4+ The relative content decreased significantly, and after cycling, it was much lower than that of Mn. 3+ The relative content indicates that the synthesized cathode underwent severe irreversible oxygen loss and structural phase transformation during cycling; while the cathode material synthesized by the three-stage calcination strategy in Comparative Example 4 showed Mn content after cycling. 4+ The relative content decreased only slightly compared to before cycling, which means that the three-stage strategy suppressed irreversible oxygen loss and structural phase transition during cycling.

[0058] Figure 6 These are HRTEM images of the cathode material in the comparative example and Example 4 (Tcs = 800°C) after 100 cycles at 1C. Figure 6 As shown in (a) of the comparative example, the cathode material synthesized by the conventional calcination process not only exhibited a disordered rock salt state (layered → spinel → rock salt state) on its surface after 100 cycles, but also a spinel phase with a disordered structure appeared near the surface. This indicates that the cathode material synthesized by the conventional calcination process underwent a severe structural phase transition; as shown in (a) of the comparative example, the cathode material synthesized by the conventional calcination process underwent a severe structural phase transition. Figure 6 As shown in (b) of Example 4 (Tcs = 800℃), the cathode material synthesized by the three-stage calcination strategy has a relatively regular and ordered near-surface layered structure after 100 cycles, and only a small amount of the layered structure transforms into the spinel phase. This means that the three-stage calcination strategy effectively suppresses the structural phase transformation of the cathode material during cycling.

[0059] In summary, compared to conventional calcination procedures, this invention successfully developed a three-stage calcination strategy to synthesize lithium-rich manganese-based cathode materials (Li1O2O3O4O5O6O7) with excellent cycle performance. 1.2 Mn0.54 Ni 0.13 Co 0.13 O2 not only helps to form an ordered and stable layered structure with less lithium-nickel mixing and higher oxygen vacancy concentration, but also reduces production energy consumption by effectively shortening the constant high temperature calcination time. This provides a reference for the future efficient, controllable, and low-cost synthesis of electrode materials with excellent cycle performance.

Claims

1. A method for synthesizing lithium-rich manganese-based cathodes using a three-stage calcination strategy, characterized in that, A three-stage calcination strategy is adopted, including the following steps: (1) The mixture of lithium-rich manganese-based cathode material precursor and lithium carbonate is heated to a first temperature at a first heating rate and then held at the temperature for a first time for pre-calcination. (2) After the precalcination is completed, the temperature is raised to the second temperature at the first heating rate, then raised to the third temperature at the second heating rate and held for a second time, then cooled to the second temperature at the first cooling rate, and finally cooled to room temperature at the second cooling rate to obtain lithium-rich manganese-based cathode material.

2. The method as described in claim 1, characterized in that, The first heating rate and the second cooling rate are both 5℃ / min, the second heating rate and the first cooling rate are both 0.5℃ / min, the first temperature is 450℃, the second temperature Tcs is 775~825℃, the third temperature is 850℃, the first holding time is 6h, and the second holding time is (3.6Tcs-2220) min.

3. The method as described in claim 1, characterized in that, The second temperature, Tcs, is 800℃.

4. The method as described in claim 1, characterized in that, The precursor of lithium-rich manganese-based cathode material has the composition of Mn 0.54 Co 0.13 Ni 0.13 CO3.

5. The method as described in claim 1, characterized in that, The mass ratio of lithium-rich manganese-based cathode material precursor to lithium carbonate is 1:0.

45.

6. The lithium-rich manganese-based cathode synthesized by the method according to any one of claims 1-5.

Images