Lithium-ion battery positive electrode active material based on low-valent multi-electron transfer redox active metal elements and its preparation method and application

Abstract

The present invention provides a lithium ion battery positive electrode active material based on a low-valent multi-electron transfer redox active metal element, characterized in that the lithium ion battery positive electrode active material has the general structural formula: Li x (M1M2) 2‑x O2, where M1 is a low-valent metal element with multi-electron redox activity; M2 is a high-valent metal element with redox inertness, 0<x<2, and the crystal structure of the lithium-ion battery positive electrode active material is a salt rock structure with a space point group of Fm-3m. The total number of anions and cations in the lithium-ion battery positive electrode active material is balanced. This lithium-ion battery positive electrode active material has high specific capacity and energy density, as well as excellent cycling performance. It can be used in fields such as 3C products and electric vehicles, and has good application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery positive electrode materials, and more specifically, to a lithium-ion battery positive electrode active material based on a low-valent multi-electron transfer redox active metal element, and a preparation method and application thereof. Background Art

[0002] Since the 19th century, fossil fuels such as coal, oil, and natural gas have supported the progress of human civilization and economic and social development. However, the non-renewable nature of fossil fuels and their massive consumption by humanity have led to their gradual depletion, resulting in increasingly serious ecological and environmental problems. Against this backdrop, the development of renewable, sustainable, and environmentally friendly new energy sources has become a consensus. Lithium-ion batteries, owing to their high specific energy, lack of memory effect, low self-discharge, long cycle life, and environmental friendliness, have been widely used in consumer electronics and electric vehicles. However, the capacity of current lithium-ion batteries is limited by their cathode materials, making them inadequate for the development of long-range electric vehicles. Therefore, the development of high-capacity cathode materials is of great significance.

[0003] Energy storage and release in lithium-ion batteries occur through redox reactions in the electrode materials, accompanied by the insertion and extraction of lithium ions. Therefore, the electrode materials play a dual role in electron migration and lithium ion transport during the charge and discharge process. Taking the positive electrode material as an example, during the battery's charging process, lithium ions are extracted from the positive electrode material's crystal lattice, accompanied by an oxidation reaction of the active element, which increases its valence to provide charge compensation. Simultaneously, electrons flow from the positive electrode to the negative electrode via an external circuit. When the battery is discharged as a power source after charging, lithium ions are inserted into the positive electrode material, and electrons flow from the negative electrode to the positive electrode via an external circuit. The active element in the positive electrode material undergoes a reduction reaction, accompanied by a decrease in its valence. Thus, the reversible redox reaction of the active element provides electron storage and release for the positive electrode and is the source of the positive electrode material's capacity. The lithium-ion battery positive electrode materials currently being studied or widely used only have high-valence active elements. For example, the valence states of Ni, Co, and Mn elements in ternary materials are 3+, 3+, and 4+, respectively; Mn in lithium manganese oxide materials is a mixed valence state of 3+ / 4+; and Co in lithium cobalt oxide materials is 3+. All of them only have single-electron transfer capabilities, which limits the improvement of the positive electrode material capacity. Summary of the Invention

[0004] Based on the above technical problems existing in the prior art, the inventors found in their research that the cation disordered salt rock structure has the advantage of a wide composition space, which can accommodate lithium ions and low-valent transition metal ions with a small radius difference at the cation site at the same time. Therefore, low-valent transition metal ions can be used as redox active centers to achieve multi-electron transfer. Based on this, one of the purposes of the present invention is to provide a lithium ion battery positive electrode active material based on a low-valent multi-electron transfer redox active metal element. The general structural formula of the lithium ion battery positive electrode active material is Li x (M1M2) 2-x O2, wherein M1 is a low-valent metal element with multi-electron redox activity; M2 is a high-valent metal element with redox inertness, 0<x<2, the crystal structure of the lithium-ion battery positive electrode active material is a salt rock structure, the space point group is Fm-3m, and the total number of anions and cations of the metal oxide is balanced.

[0005] In some embodiments, 1≤x<1.5.

[0006] In some embodiments, the M1 is Co 2+ 、Mn 2+ 、Ni 2+ Cr 3+ 、V 3+ 、 Mo 3+ 、Fe 2+ At least one of; said M2 is Ti 4+ 、Zr 4+ 、Mn 4+ 、Nb 5+ 、Ta 5+ 、W 6+ 、Mo 6+ At least one of .

[0007] In some embodiments, the M1 is Co 2+ 、Mn 2+ 、Ni 2+ Cr 3+ 、V 3+ 、 Mo 3+ 、Fe 2+ One of them, M2 is Ti 4 + 、Zr 4+ 、Mn 4+ 、Nb 5+ 、Ta 5+ 、W 6+ 、Mo 6+ One of , and M1 and M2 are different elements.

[0008] A second object of the present invention is to provide a method for preparing a positive electrode active material for a lithium-ion battery based on a low-valent multi-electron transfer redox active metal element according to any of the above embodiments, the preparation method comprising the following steps:

[0009] S1. Fully mixing a compound having elements M1 and M2 and a lithium source to obtain a precursor;

[0010] S2, after fully mixing the precursor with molten salt, sintering at high temperature, and cooling to obtain the lithium ion battery positive electrode active material;

[0011] The high temperature sintering is specifically as follows: firstly heating the temperature to 300-600°C for pre-sintering, and then heating the temperature to 900-1200°C for sintering.

[0012] In some embodiments, the molar ratio of the molten salt to the precursor is 1 to 10:1.

[0013] In some embodiments, the molten salt is at least one of NaCl, KCl, Na2SO4, K2SO4, NaNO3, and KNO3.

[0014] In some embodiments, the lithium source is at least one of Li2CO3, LiOH, and Li2O.

[0015] In some embodiments, the compounds of M1 and M2 include but are not limited to compounds containing only M1 element, compounds containing only M2 element, and compounds containing both M1 and M2 elements. Specifically, they include but are not limited to at least one of the carbonates, nitrates, chlorides, and oxides of M1 and M2; more specifically, they include but are not limited to at least one of the carbonates, nitrates, chlorides, and oxides of M1 element; at least one of the carbonates, nitrates, chlorides, and oxides of M2 element; oxides containing both M1 and M2, etc.

[0016] In some embodiments, the pre-sintering time is 2 to 6 hours; and the sintering time is 6 to 24 hours.

[0017] In some embodiments, the temperature is raised to the pre-sintering temperature at a rate of 3 to 5° C. / min. After the pre-sintering is completed, the temperature is further raised to the sintering temperature at a rate of 3 to 5° C. / min.

[0018] In some embodiments, after sintering is completed, the furnace is cooled to room temperature.

[0019] In some embodiments, after cooling, the process further comprises the following steps: washing, separating, and drying the obtained product to obtain the lithium-ion battery positive electrode active material.

[0020] A third object of the present invention is to provide a positive electrode plate, which includes the above-mentioned lithium-ion battery positive electrode active material.

[0021] A fourth object of the present invention is to provide a lithium-ion battery comprising the above-mentioned positive electrode sheet.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention uses lithium ion metal oxides prepared by combining low-valent metal ions with multi-electron redox activity with high-valent metal ions without redox activity as the positive electrode active material of the lithium ion battery. Among them, the low-valent metal ions with multi-electron transfer activity serve as carriers for electron storage and release, and can achieve multi-electron transfer during the charge and discharge process, ensuring nearly twice the capacity output with the same active element content. The high-valent redox-inert metal ions can form a stable spatial structure with the low-valent metal, making the space group of the crystal Fm-3m, thereby making the lithium ion battery positive electrode active material have higher stability during use, thereby making the lithium ion battery positive electrode active material have high capacity output and excellent cycle stability.

[0024] The present invention breaks through the composition design limitations of traditional lithium-ion battery positive electrode active materials and provides a new high-capacity lithium-ion battery positive electrode active material. The lithium-ion battery positive electrode active material has high specific capacity and energy density, as well as excellent cycle performance. It can be used in 3C products and electric vehicles and other fields, and has good commercial application prospects.

[0025] The preparation method provided by the present invention uses a low-melting-point molten salt as a reaction medium, forming a liquid-phase reaction environment during high-temperature treatment, in which partially dissolved reactants can quickly migrate, greatly accelerating the reaction speed and lowering the reaction temperature. By regulating the type and mass ratio of the molten salt, controllable growth of the crystal nucleus can be achieved.

[0026] In addition, the preparation method of the present invention can prepare single-crystal metal oxides in a spherical shape and effectively avoid particle agglomeration, so that the obtained lithium-ion battery positive electrode active material has a particle size of 1 to 5 μm and a uniform grain size. Compared with the traditional solid-phase reaction synthesis method, molten salt assistance can provide a liquid environment for multiphase solid-phase reaction, block the growth of grain boundaries, modify the single crystal morphology, and at the same time reduce and homogenize the grain size, avoiding subsequent grinding treatment. In addition, molten salt can isolate the air and prevent low-valent active elements from being oxidized to high-valent states by air during the calcination process. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The process flow for preparing the positive electrode active material of the lithium ion battery of the present invention;

[0028] Figure 2 Li in Example 1 1.2 Co 0.4 Nb 0.4 XRD pattern of O2;

[0029] Figure 3 Li in Example 1 1.2 Co 0.4 Nb 0.4 SEM image of O2;

[0030] Figure 4 Li in Example 1 1.2 Co 0.4 Nb 0.4 The charge and discharge curve of O2;

[0031] Figure 5 Li in Example 1 1.2 Co 0.4 Nb 0.4 O2 cycle performance diagram;

[0032] Figure 6 Li in Example 2 1.2 Ni 0.4 Nb 0.4 XRD pattern of O2;

[0033] Figure 7 Li in Example 2 1.2 Ni 0.4 Nb 0.4 SEM image of O2;

[0034] Figure 8 Li in Example 2 1.2 Ni 0.4 Nb 0.4 The charge and discharge curve of O2;

[0035] Figure 9 Li in Example 2 1.2 Ni 0.4 Nb 0.4 O2 cycle performance diagram;

[0036] Figure 10 is the SEM image of LiCoO2 in Comparative Example 1;

[0037] Figure 11 is the XRD pattern of LiCoO2 in Comparative Example 1;

[0038] Figure 12 The charge and discharge curve of LiCoO2 in Comparative Example 1 (1.5-4.4V);

[0039] Figure 13The cycle performance diagram of LiCoO2 in Comparative Example 1 (1.5-4.4V);

[0040] Figure 14 The charge and discharge curve of LiCoO2 in Comparative Example 1 (1.5-4.3V);

[0041] Figure 15 This is the cycle performance diagram of LiCoO2 in Comparative Example 1 (1.5-4.3V). DETAILED DESCRIPTION

[0042] The following description sets forth numerous specific details to facilitate a thorough understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific implementations disclosed below.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0044] Example 1

[0045] This embodiment provides a lithium-ion battery positive electrode active material based on a low-valent multi-electron transfer redox active metal element, the chemical formula of which is Li 1.2 Co 2+ 0.4 Nb 5+ 0.4 O2, the preparation method of the lithium ion battery positive electrode active material is as follows Figure 1 As shown, the following steps are included:

[0046] S1. Li2CO3, CoCO3, and Nb2O5 are weighed and mixed according to the stoichiometric ratio to obtain a precursor, wherein Li2CO3 and CoCO3 are in excess of 10% and 5%, respectively, to prevent loss during high-temperature sintering; the precursors are mixed uniformly by ball milling to obtain a precursor powder;

[0047] S2. Weigh the precursor powder, add KCl molten salt with a molar ratio of 1:1 to Li2CO3 and mix well; then place the precursor powder in a tube furnace and perform high-temperature sintering under argon atmosphere; wherein the high-temperature sintering is divided into two steps, the first step is pre-sintering, the pre-sintering temperature is 600°C, and the pre-sintering time is 3h; the second step is sintering at a temperature of 1000°C and a sintering time of 6h; the heating rate of the two sintering steps is controlled at 3°C / min; the cooling process adopts furnace cooling;

[0048] S3, the obtained product was washed with distilled water and filtered, then washed with distilled water and ethanol 3 times each, and dried under vacuum at 80 ° C for 6 h to obtain Li 1.2 Co 2+ 0.4 Nb 5+ 0.4 O2 lithium-ion battery cathode active material.

[0049] The XRD pattern of the positive electrode active material of the lithium ion battery obtained in this example is shown in Figure 2 The XRD spectrum shows that its structure is salt rock structure, and the space point group is Fm-3m; its SEM picture is as follows Figure 3 As shown in the figure, the prepared lithium-ion battery positive electrode active material is spherical and has a particle size distribution of 1-5 μm.

[0050] The Li 1.2 Co 2+ 0.4 Nb 5+ 0.4 O2 lithium ion battery positive electrode active material is made into positive electrode sheet, specifically: 1.2 Co 2+ 0.4 Nb 5+ 0.4 O2 powder was mixed with acetylene black and polyvinylidene fluoride (PVDF, adhesive) in a mass ratio of 70:20:10, and an appropriate amount of N-methylpyrrolidone (NMP) solution was added as a dispersant. The mixture was magnetically stirred for 2 hours to prepare a slurry. The slurry was then coated on an aluminum foil current collector, vacuum dried at 120°C for 8 hours, and transferred to an Ar atmosphere glove box for use.

[0051] Half-cells were assembled in an Ar atmosphere glove box, using metallic lithium as the counter electrode and a LiPF6 / ethylene carbonate (EC:DMC:DEC = 1:1:1) solution as the electrolyte, forming CR2016 button cells. Charge and discharge tests were conducted using a galvanostatic charge / discharge mode at a current density of C / 10 (20 mA / g), with a charge cutoff voltage of 4.4 V and a discharge cutoff voltage of 1.5 V.

[0052] The electrochemical performance test results of the lithium ion battery positive electrode active material prepared in this embodiment are as follows: Figure 4 and Figure 5 shown.

[0053] Example 2

[0054] This embodiment provides a lithium-ion battery positive electrode active material based on a low-valent multi-electron transfer redox active metal element, the chemical formula of which is Li 1.2 Ni 2+ 0.4 Nb5+ 0.4 O2, the preparation method of the lithium ion battery positive electrode active material is as follows Figure 1 As shown, the following steps are included:

[0055] S1. Li2CO3, NiCO3, and Nb2O5 are weighed and mixed according to the stoichiometric ratio to obtain a precursor, wherein Li2CO3 and NiCO3 are in excess of 10% and 5%, respectively, to prevent loss during high-temperature sintering; the precursors are mixed uniformly by ball milling to obtain a precursor powder;

[0056] S2. Weigh the precursor powder, add KCl molten salt with a molar ratio of 1:1 to Li2CO3 and mix well; then place the precursor powder in a tube furnace and perform high-temperature sintering under argon atmosphere; wherein the high-temperature sintering is divided into two steps, the first step is pre-sintering, the pre-sintering temperature is 600°C, and the pre-sintering time is 3h; the second step is sintering at a temperature of 1000°C and a sintering time of 6h; the heating rate of the two sintering steps is controlled at 3°C / min; the cooling process adopts furnace cooling;

[0057] S3, the obtained product was washed with distilled water and filtered, then washed with distilled water and ethanol 3 times each, and dried under vacuum at 80 ° C for 6 h to obtain Li 1.2 Ni 2+ 0.4 Nb 5+ 0.4 O2 lithium ion battery positive electrode active material. The XRD spectrum of the lithium ion battery positive electrode active material of this embodiment is shown in Figure 6 , SEM pictures are as follows Figure 7 shown.

[0058] The Li prepared in this example 1.2 Ni 2+ 0.4 Nb 5+ 0.4 The positive electrode sheet was made from the positive active material of the O2 lithium-ion battery and a lithium-ion half-cell was assembled. Charge and discharge tests were conducted using a constant current charge / discharge mode at a current density of C / 10 (20 mA / g), with a charge cutoff voltage set at 4.3 V and a discharge cutoff voltage set at 1.5 V.

[0059] The electrochemical performance test results of the lithium ion battery positive electrode active material prepared in this example are shown in Figure 8 and Figure 9 .

[0060] Comparative Example 1

[0061] This comparative example provides a traditional lithium ion battery positive electrode active material LiCo 3+O2, the preparation method thereof is specifically as follows: Li2CO3 and CoCO3 are weighed according to the stoichiometric ratio, wherein Li2CO3 and CoCO3 are respectively in excess of 10% and 5% to prevent loss during high-temperature sintering; the precursors are mixed uniformly by ball milling to obtain precursor powder; then, the temperature is raised to 1000°C at a heating rate of 2°C / min in a pure oxygen atmosphere, and the temperature is kept for 12 hours and then cooled in the furnace to obtain the positive electrode active material LiCo of the lithium ion battery. 3+ O2. The obtained lithium-ion battery positive electrode active material LiCo 3+ The XRD pattern of O2 can be found in Figure 11 , XRD spectrum shows that the obtained LiCo 3+ O2 has an R-3m structure; its SEM image is as follows Figure 10 shown.

[0062] The prepared LiCo 3+ The positive electrode sheet was made of O2 material and the lithium ion half-cell was assembled. The charge and discharge test was carried out at a current density of 20mA / g using the constant current charge and discharge mode. The charge cut-off voltage was set to 4.4V and the discharge cut-off voltage was set to 1.5V. The test results are as follows: Figure 12 As shown in Figure 13. Using the constant current charge and discharge mode, the charge and discharge test was carried out at a current density of 20mA / g, the charge cut-off voltage was set to 4.3V, and the discharge cut-off voltage was set to 1.5V. The test results are shown in Figure 13. Figure 14 and Figure 15 shown.

[0063] contrast Figure 3 、 Figure 7 and Figure 10 The molten salt-assisted solid-phase reaction can modify the morphology of the precursor and block the grain boundary propagation growth during the high-temperature reaction process, thereby obtaining spherical single crystals with uniform morphology and a particle size of 1-3 microns. The materials synthesized by the solid-phase method have a wider particle size distribution after grinding, which shows that the molten salt method can effectively homogenize the grain size.

[0064] contrast Figure 4 and Figure 12 , at a charge cut-off voltage of 4.4 V, based on the low-valent multi-electron transfer oxidation active element Co 2+ Li 1.2 Co 2+ 0.4 Nb 5+ 0.4 The first cycle discharge capacity of O2 is 210.8 mAh / g, which is higher than the traditional LiCoO2 181.1 mAh / g. Figure 5 and Figure 13 , Li 1.2 Co 2+ 0.4 Nb5+ 0.4 The 30-cycle specific capacity retention rate of O2 reaches 87.9%, which is much higher than the 30-cycle specific capacity retention rate of traditional LiCoO2 of 77.7%.

[0065] contrast Figure 8 and Figure 14 , Figure 9 and Figure 15 , set the charge cut-off voltage to 4.3V, under the condition that the initial specific capacity is not much different, based on the multi-electron transfer oxidation active element Ni 2+ Li 1.2 Ni 2+ 0.4 Nb 5+ 0.4 The specific capacity retention rate of O2 after 30 cycles is 89.2%, which is much higher than the specific capacity retention rate of traditional LiCoO2 after 30 cycles of 79.8%.

[0066] The above results show that the lithium-ion battery positive electrode active material based on low-valent multi-electron transfer redox active metal elements provided by the present invention is applied to secondary batteries and exhibits ultra-high capacity and good cycle performance.

[0067] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0068] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A lithium-ion battery cathode active material based on a low-valent multi-electron transfer redox active metal element, characterized in that: The general structural formula of the positive electrode active material of the lithium ion battery is: Li x (M1M2) 2-x O2, where M1 is Co 2+ or Ni 2+ , M2 is Nb 5+ , x=1.2; the crystal structure of the positive electrode active material of the lithium ion battery is a salt rock structure, the space point group is Fm-3m, and the total number of anions and cations in the positive electrode active material of the lithium ion battery is balanced; The preparation method comprises the following steps: S1. Fully mixing a compound having elements M1 and M2 and a lithium source to obtain a precursor; S2, after fully mixing the precursor with molten salt KCl, sintering at high temperature, and cooling to obtain the lithium ion battery positive electrode active material; The high temperature sintering is specifically as follows: firstly heating the temperature to 600°C for pre-sintering, and then heating the temperature to 1000°C for sintering; The molar ratio of the molten salt to the precursor is 1:

1.

2. The method for preparing the positive electrode active material for a lithium ion battery according to claim 1, comprising the following steps: S1. Fully mixing a compound having elements M1 and M2 and a lithium source to obtain a precursor; S2, after fully mixing the precursor with molten salt KCl, sintering at high temperature, and cooling to obtain the lithium ion battery positive electrode active material; The high temperature sintering is specifically as follows: firstly heating the temperature to 600°C for pre-sintering, and then heating the temperature to 1000°C for sintering; The molar ratio of the molten salt to the precursor is 1:

1.

3. The method for preparing a positive electrode active material for a lithium ion battery according to claim 2, wherein: The temperature is raised to the pre-sintering temperature at a rate of 3 to 5°C / min. After the pre-sintering is completed, the temperature is raised to the sintering temperature at a rate of 3 to 5°C / min; and / or, the pre-sintering time is 2 to 6 hours; the sintering time is 6 to 24 hours.

4. A positive electrode plate, characterized in that: The invention comprises the lithium ion battery positive electrode active material according to claim 1 or the lithium ion battery positive electrode active material obtained by the preparation method according to any one of claims 2 to 3.

5. An electrochemical energy storage device, characterized in that Including the positive electrode sheet according to claim 4.

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