Lithium ion battery layer oxygen structure positive electrode material regeneration method based on deep charging and defect active homogenization

Abstract

The invention discloses a method for regenerating a lithium ion battery layer oxygen structure positive electrode material based on deep charging and defect active homogenization, and belongs to the technical field of waste lithium ion battery recovery and positive electrode material regeneration. The method comprises the following steps: firstly, deeply charging a decommissioned lithium ion battery to obtain a lithium-removed positive electrode; the method comprises the following core steps: carrying out controllable heat treatment on a lithium-removed positive electrode, and actively driving and converting heterogeneous defect phases (such as a spinel phase and a rock salt phase) in a material into a single-phase rock salt phase precursor with uniform stoichiometry by utilizing the characteristic of thermally induced phase change (lamellar-spinel-rock salt) of the lithium-removed positive electrode, so as to realize'defect homogenization '. And then, supplementing lithium for the homogeneous precursor, and sintering to realize lattice reconstruction and performance recovery. Passive repair is changed into active drive, a phase change path is accurately controlled by constructing a heat treatment phase diagram, the bottleneck that atomic scale homogeneous regeneration is difficult to realize by a traditional method is solved, the process is simple, the cost is low, and the regenerated positive electrode is excellent in performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery recycling technology, specifically to a method for efficient and homogeneous regeneration of oxygen-layer structure cathode materials from retired lithium-ion batteries, and more particularly to a direct regeneration method based on deep charging pretreatment and utilizing the intrinsic thermal phase transition of the material to achieve active homogenization of defects. Background Technology

[0002] With the rapid development of electric vehicles, a large number of lithium-ion batteries are nearing the end of their service life. Ternary cathode materials (NCM / NCA) contain high-value elements such as nickel, cobalt, manganese, and lithium, making their recycling and regeneration crucial. Current recycling technologies are mainly divided into pyrometallurgy, hydrometallurgy, and direct recycling methods. Pyrometallurgy and hydrometallurgy aim to extract metal elements, but these processes are lengthy, energy-intensive, and difficult to preserve the high-value structure of the cathode material. Direct recycling methods focus on repairing the damaged cathode material structure, offering greater economic and environmental potential.

[0003] However, existing direct regeneration technologies face a bottleneck in the homogeneity of regenerated cathodes: retired cathode materials are complex systems containing multiphase heterogeneity, including bulk layered structures, near-surface spinel phases, and surface rock salt phases. The traditional "lithium replenishment-re-sintering" repair strategy is passive and cannot fundamentally eliminate these heterogeneous defects, resulting in non-uniformity of the regenerated material at both the atomic and microscale, and limited recovery of electrochemical performance. While the molten salt method can adequately replenish lithium, it is costly, involves complex post-processing, and similarly struggles to address the initial heterogeneity problem.

[0004] Therefore, developing a new method capable of uniform regeneration is a technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for regenerating lithium-ion battery layered oxygen structure cathode materials. This method innovatively utilizes the inherent thermally induced phase transition law of delithiated cathode materials, transforming "passive repair" into "active driving," converting heterogeneous defects into homogeneous precursors, laying the foundation for subsequent high-quality lattice reconstruction, and ultimately obtaining high-performance regenerated cathode materials.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for regenerating a lithium-ion battery layered oxide structure cathode material includes the following steps:

[0008] Step 1: Deep charge the lithium-ion battery with the decommissioned layered oxide structure cathode material (deep charge to its upper voltage limit or higher, such as 4.5V or higher) to remove as much lithium as possible from the cathode; then safely disassemble the battery and separate the cathode electrode.

[0009] Step 2: Separate the delithiated positive electrode active material from the delithiated positive electrode sheet;

[0010] The positive electrode obtained in step one is separated and collected from current collectors such as aluminum foil by physical methods;

[0011] Step 3: The delithiation state positive electrode active material is subjected to a first-stage heat treatment in an oxygen-containing atmosphere to cause a directional phase transition in its crystal structure, transforming it into a homogeneous precursor dominated by rock salt phase.

[0012] The delithiated cathode powder obtained in step two is placed in a tube furnace or similar equipment and subjected to a controlled first-stage heat treatment in an oxygen-containing atmosphere (such as air) to obtain a homogeneous rock salt phase precursor. This step is the core innovation: delithiated layered oxide cathode materials, especially ternary oxides, undergo a phase transition following a clear thermodynamic path upon heating: layered structure → spinel structure → rock salt structure. By precisely controlling the heat treatment temperature (T) and time (t), all heterogeneous regions in the material (including the originally existing defective spinel and rock salt phases) can be actively and synchronously "driven" to a unified, thermodynamically stable endpoint—the rock salt phase. This process is called "active homogenization of defects," which creates an ideal precursor platform with stoichiometric homogeneity and a single phase structure. The process can be precisely guided by experimentally establishing a "Tt-Phase" three-dimensional phase diagram for specific materials.

[0013] Step four: Add lithium source to the homogeneous precursor obtained in step three, mix evenly, and then perform a second-stage heat treatment in an oxygen-containing atmosphere to regenerate a ternary cathode material with a layered structure.

[0014] A stoichiometric lithium source (such as Li₂CO₃) is added to the homogeneous rock salt phase precursor obtained in step three and mixed thoroughly. Then, a second-stage high-temperature re-sintering is performed in an oxygen-containing atmosphere. During this process, lithium ions are re-intercalated into the rock salt phase lattice, driving a reverse phase transition and reconstructing an ordered layered crystal structure. Because the precursor is highly homogeneous before the second-stage high-temperature re-sintering, the recrystallization process during this second-stage high-temperature re-sintering can achieve uniform nucleation and growth at the atomic scale, thereby obtaining a regenerated ternary cathode material with a uniform microstructure and excellent electrochemical performance (approaching or reaching the level of virgin material).

[0015] The lithium battery cathode material mentioned in the steps includes cathode materials with various layered oxygen structures, such as LiCoO2, NMC ternary materials, and other lithium battery cathode materials with different structures.

[0016] The cutoff voltage for deep charging in step one is 100%-120% of the battery's rated upper limit voltage.

[0017] Step 2 involves separating the delithiated positive electrode active material from the aluminum foil current collector by crushing, sieving, and / or ultrasonic peeling.

[0018] In step three, the first stage of heat treatment is carried out at a temperature of 300℃ to 600℃ for 1 to 10 hours. The oxygen-containing atmosphere is air, oxygen, or a mixture of oxygen and an inert gas. The specific heat treatment process parameters are selected and controlled based on the Tt-Phase three-dimensional phase diagram established for the delithiated cathode material, with the aim of precisely controlling the complete transformation of the material into the rock salt phase.

[0019] In step four, the supplemented lithium source is at least one of lithium carbonate, lithium hydroxide, lithium nitrate, or lithium acetate; the amount of supplemented lithium is calculated based on the stoichiometric ratio (Li / transition metal) of the target recycled material, and an additional 0-10% excess lithium is added to compensate for losses during the sintering process.

[0020] Step four, the second stage of high-temperature re-sintering is carried out at a temperature of 500-1000℃ (more preferably 700-900℃) for 5-15 hours.

[0021] The present invention has the following beneficial effects: (1) It proposes and utilizes the thermally induced phase transition law of the delithiation state cathode for the first time, taking heterogeneous defects as the "intrinsic driving force" for homogenization, and realizing the fundamental transformation from a multiphase heterogeneous system to a single-phase homogeneous precursor through "active driving" rather than "passive repair". This provides a perfect starting point for subsequent lattice uniform reconstruction and breaks through the bottleneck of non-uniformity of recycled materials in traditional methods; (2) It introduces the concept of "thermal treatment phase diagram" to guide the homogenization process, so that the process shifts from experience trial and error to precise control, improving the reproducibility of the regeneration process and product consistency; (3) It avoids complex molten salt systems or strong acid leaching processes, the process is relatively short, and the energy consumption and chemical consumption are low, which is a green and economical direct regeneration strategy; (4) The cathode material obtained by regeneration can be comparable to commercial new materials in terms of crystal structure integrity, element distribution uniformity, and electrochemical performance such as specific capacity and cycle life, and has extremely high reuse value. Attached Figure Description

[0022] Figure 1 The performance of the case study (NCM ternary cathode) before and after regeneration, as well as the microstructure characterization of the sample, are presented. Among them:

[0023] (a) The figure shows the charge-discharge curves of waste NCM523 positive electrode at room temperature of 25℃, voltage range of 3-4.3V, and 0.1C rate (1C = 180mAh / g).

[0024] (b) The figure shows the case study: the first charge-discharge curve of the regenerated NCM523 cathode at room temperature of 25℃, voltage range of 3-4.3V, and 0.1C rate (1C = 180mAh / g).

[0025] (c) The figure shows a case study: the capacity retention of the regenerated NCM523 cathode was 75% after 200 cycles at room temperature of 25℃, voltage range of 3-4.3V, and 0.1C rate (1C = 180mAh / g).

[0026] (d) The figure shows a case study: the atomic structure distribution of the regenerated NCM523 cathode is uniform. Detailed Implementation

[0027] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0028] Example 1

[0029] Step 1: After the waste NCM523 battery is left to stand for 12 hours on the battery testing system, it is charged to 4.5 V at a rate of 0.1C (where 1C = 180 mA / g), and then kept in a constant voltage charging state.

[0030] Step 2: Quickly immerse the NCM523 battery from Step 1 into a liquid nitrogen (-196 ℃) freezing environment to ensure that the electrolyte in the battery is quickly and fully frozen. Then, remove the battery and quickly disassemble it in a freezing and inert gas environment to obtain the waste NCM523 positive electrode sheet in a charging state.

[0031] Step 3: The waste NCM523 positive electrode sheet obtained in Step 2 and charged to 4.5 V is crushed, dissolved, washed and dried to obtain waste NCM523 positive electrode powder.

[0032] Step four: The waste NCM523 cathode powder obtained in step three is calcined in air at 350°C for 4 hours, and then cooled to room temperature in the furnace to obtain NCM oxide with uniform phase structure.

[0033] Step five: The NCM oxide obtained in step four is mixed with lithium according to the stoichiometric ratio, then calcined at 800°C for 8 hours in an oxygen-containing atmosphere, followed by furnace cooling to room temperature to obtain regenerated NCM523 cathode powder. In the case study, the sample was used in a battery for cycle performance testing, such as... Figure 1 The regenerated cathode exhibits a uniform microstructure, resulting in improved performance.

Claims

1. A method for recycling lithium ion battery layered-oxide cathode materials based on deep charging and active homogenization of defects, characterized in that, The method comprises the following steps: Step one, deep charge the retired lithium ion battery containing layered oxygen structure cathode material to its upper limit voltage or higher, then disassemble to obtain delithiated cathode sheet; Step two, separate delithiated cathode active material from the delithiated cathode sheet; Step three, perform first stage heat treatment on the delithiated cathode active material in an oxygen-containing atmosphere to make the crystal structure thereof undergo directional phase change and be converted into a homogeneous precursor mainly in rock salt phase; Step four, supplement lithium source to the homogeneous precursor obtained in step three, mix uniformly, and then perform second stage heat treatment in an oxygen-containing atmosphere to make the material regenerate into ternary cathode material with layered structure.

2. The method according to claim 1, characterized in that The cut-off voltage of the deep charge in step one is 100%-120% of the upper limit voltage of the battery.

3. The method of claim 1, wherein, The temperature of the first stage heat treatment in step three is 300-600 DEG C, and the holding time is 1-10 hours; the oxygen-containing atmosphere is air, oxygen or a mixture of oxygen and inert gas.

4. The method of claim 3, wherein, The heat treatment process parameters in step four are selected and controlled based on the T-t-Phase three-dimensional phase diagram established for the delithiated cathode material to accurately control the complete conversion of the material into rock salt phase.

5. The method of claim 1, wherein, In step five, the supplemented lithium source is at least one of lithium carbonate, lithium hydroxide, lithium nitrate or lithium acetate; the amount of lithium supplement is calculated according to the stoichiometric ratio (Li / transition metal) of the target regenerated material, and 0-10% excess lithium is additionally added to compensate for the loss in the sintering process.

6. The method according to claim 1 or 5, characterized in that, In step five, the temperature of the second stage heat treatment is 500-1000 DEG C, and the holding time is 5-15 hours.

7. The method of claim 1, wherein, In step three, the delithiated cathode active material is separated from the aluminum foil current collector by means of crushing, screening and / or ultrasonic peeling.

8. The method of claim 1, wherein, The layered oxygen structure cathode material is selected from LiCoO2, ternary material and other lithium battery cathode materials.

9. A positive electrode material of a layered oxygen structure, characterized by It is regenerated by the method of any one of claims 1-7.

10. A lithium-ion battery, characterized by, The cathode thereof comprises the layered oxygen structure cathode material of claim 9.

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