A germanium-doped lithium-rich manganese-based positive electrode material, a preparation method thereof and a battery

Abstract

The application relates to the technical field of lithium ion batteries, and discloses a germanium-doped lithium-rich manganese-based positive electrode material, a preparation method thereof and a battery, steps of which are as follows: a Ni 0.25 Mn 0.75 CO3 precursor is prepared by adopting a carbonated co-precipitation method of a continuous stirring reaction kettle; the above Ni 0.25 Mn 0.75 CO3 precursor is fully ground and uniformly mixed with Li in a lithium source and a germanium source according to a certain proportion; the mixture is placed in a high-temperature calcining furnace to perform calcining under an air atmosphere, and a germanium-doped lithium-rich manganese-based positive electrode material modified by germanium ions is prepared after annealing; the germanium-doped lithium-rich positive electrode material is realized by adopting a one-step sintering method, and nanometer-scale fast-ion conductor lithium germanate coating is realized; germanium ions are introduced in a crystal lattice to induce Ni 2+ oxidation, cation order of the material is improved, the nanometer-scale fast-ion conductor lithium germanate coating can effectively isolate interface side reactions of the electrode material, lithium ion transmission is accelerated, the structural stability of the battery material is improved, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a germanium-doped lithium-rich manganese-based cathode material, its preparation method, and a battery thereof. Background Technology

[0002] With the increasing demand for energy storage driven by social development, developing energy storage battery devices with higher energy density is a necessary strategy to meet the needs of social development and promote sustainable development. Therefore, the preparation of lithium-rich manganese-based cathode materials with high specific capacity has become one of the important pathways for the development of high-energy-density lithium-ion batteries.

[0003] However, the ultra-high energy density of lithium-rich manganese-based batteries mainly relies on anionic redox reactions occurring at high voltage (4.8V). But when anions participate in the charge compensation process, they can easily cause changes in the crystal structure of the material itself, leading to irreversible phase transitions and resulting in problems such as voltage hysteresis and voltage decay. Currently, modification methods such as bulk / surface ion doping, surface coatings, and interface treatments are generally used to stabilize the crystal structure of lithium-rich materials, thereby improving their electrochemical performance.

[0004] Applying coatings to the surface of lithium-rich cathode materials through wet chemical coating reactions and secondary high-temperature calcination is a common modification method. However, this conventional coating method usually involves an additional subsequent calcination process, which not only increases the energy consumption in the material modification process, but also increases the corresponding time cost.

[0005] In view of the above, this application is hereby submitted. Summary of the Invention

[0006] The problem with existing technologies is that coating and modifying the surface of lithium-rich cathode materials using wet chemical coating reactions and secondary high-temperature calcination requires additional subsequent calcination processes, which not only increases energy consumption but also time costs. The purpose of this invention is to provide a germanium-doped lithium-rich manganese-based cathode material, its preparation method, and a battery. This invention employs a one-step sintering method to simultaneously achieve germanium doping of the lithium-rich cathode material and the nanoscale fast-ion conductor lithium germanate coating. This is achieved by introducing germanium ions into the crystal lattice to induce Ni… 2+ Oxidation occurs, enhancing the cation order of the material. The nanoscale fast-ion conductor lithium germanate coating can effectively isolate the interfacial side reactions of the electrode material, while accelerating lithium-ion transport, improving the structural stability of the battery material, and thus improving the battery cycle performance.

[0007] This invention is achieved through the following technical solution:

[0008] In a first aspect, the present invention provides a germanium-doped lithium-rich manganese-based cathode material, comprising a germanium ion-doped lithium-rich manganese-based cathode material matrix and a fast ion conductor lithium germanate coating layer, wherein the fast ion conductor lithium germanate coating layer coats the outside of the germanium ion-doped lithium-rich manganese-based cathode material matrix to form a core-shell structure.

[0009] In one specific embodiment, the fast ion conductor lithium germanate on the coating layer is nanoscale.

[0010] The germanium-doped lithium-rich manganese-based cathode material of the present invention can induce Ni by introducing germanium ions into the crystal lattice. 2+ Oxidation occurs, enhancing the cationic order of the material; by coating the outside with a nanoscale fast-ion conductor lithium germanate coating, the interfacial side reactions of the electrode material can be effectively isolated, while accelerating lithium-ion transport, improving the structural stability of the battery material, and thus improving the battery cycle performance.

[0011] Secondly, this invention provides a method for preparing a germanium-doped lithium-rich manganese-based cathode material, wherein Ni... 0.25 Mn 0.75 The mixture of CO3 precursor, lithium source and germanium-doped source is prepared by one-step high-temperature calcination.

[0012] In a specific embodiment, the preparation method is as follows:

[0013] Ni was prepared by carbonate coprecipitation in a continuously stirred reactor. 0.25 Mn 0.75 CO3 precursor;

[0014] The above Ni 0.25 Mn 0.75 The CO3 precursor is thoroughly ground and uniformly mixed with the Li and germanium sources in the lithium source in a certain proportion.

[0015] The mixture was placed in a high-temperature calcination furnace and calcined in air atmosphere. After annealing, germanium-modified germanium-doped lithium-rich manganese-based cathode material was obtained.

[0016] In one specific embodiment, the lithium source is Li2CO3 or LiOH, and the germanium doping source is GeO2.

[0017] In a particular implementation, the Ni 0.25 Mn 0.75 The molar ratio of Li to GeO2 in the CO3 precursor and lithium source is 1:1.5:(0.01~0.05).

[0018] In one specific embodiment, the high-temperature calcination includes pre-calcination and high-temperature calcination. The pre-calcination temperature is 450–550°C and the calcination time is 4–6 h. The high-temperature calcination temperature is 800–900°C and the calcination time is 10–14 h. The calcination is carried out at a heating rate of 3–5°C / min.

[0019] This invention employs a one-step sintering method to simultaneously achieve germanium doping of lithium-rich cathode materials and nanoscale fast ion conductor lithium germanate coating. This eliminates the secondary calcination process in commonly used modification preparation methods for lithium-rich manganese-based cathode materials, reducing energy consumption and time costs in the preparation process and facilitating the industrial application and promotion of lithium-rich manganese-based cathode materials.

[0020] Thirdly, the present invention provides an application of germanium-doped lithium-rich manganese-based cathode material in lithium-ion batteries.

[0021] In a specific embodiment, the application method is as follows: the germanium-doped lithium-rich manganese-based cathode material is mixed with a conductive agent, a binder (PVDF) and a conductive agent (carbon black) in a mass ratio of 8:1:1, and uniformly coated on an aluminum foil. The coated electrode is then vacuum dried, and the prepared electrode is cut and weighed according to the battery assembly requirements.

[0022] In one specific implementation, the battery assembly uses a lithium sheet as the negative electrode, and the positive electrode sheet is assembled into a button cell in a glove box.

[0023] Fourthly, the present invention provides a lithium-ion battery comprising a positive electrode and a negative electrode, wherein the positive electrode is made of the germanium-doped lithium-rich manganese-based positive electrode material.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] 1. The present invention provides a germanium-doped lithium-rich manganese-based cathode material, which can induce Ni by introducing germanium ions into the crystal lattice. 2+ Oxidation occurs, enhancing the cation order of the material; by coating the outside with a nanoscale fast-ion conductor lithium germanate coating, the interfacial side reactions of the electrode material can be effectively isolated, while accelerating lithium-ion transport, improving the structural stability of the battery material, and achieving improved battery cycle performance.

[0026] 2. The method for preparing germanium-doped lithium-rich manganese-based cathode material provided in this embodiment of the invention adopts a one-step sintering method to simultaneously achieve germanium doping of lithium-rich cathode material and nanoscale fast ion conductor lithium germanate coating. This eliminates the secondary calcination process in commonly used modification preparation methods for lithium-rich manganese-based cathode materials, reduces energy consumption and time costs in the preparation process, and is conducive to the industrial application and promotion of lithium-rich manganese-based cathode materials. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the crystal structure of the tetravalent germanium ion-doped lithium-rich cathode material prepared according to an embodiment of the present invention;

[0029] Figure 2 XRD patterns (a) and 003 diffraction peak patterns (b) of the germanium-doped lithium-rich manganese-based cathode material prepared in the embodiments of the present invention and the comparative examples;

[0030] Figure 3 XPS full spectrum and fine elemental spectra of Ni, Mn and Ge of the germanium-doped lithium-rich manganese-based cathode material prepared in the embodiments of the present invention and the comparative examples;

[0031] Figure 4 TEM images of the cathode material prepared for comparative example (ae) and the germanium-doped lithium-rich manganese-based cathode material prepared in Example 2 of the present invention (fj), and elemental distribution diagram of Example 2 (ko);

[0032] Figure 5 The cycling performance (a) and corresponding average voltage decay curve (b) of the electrode material prepared for the embodiments of the present invention at 1C current; the charge-discharge curves (cd) of G0 and G2 electrode materials and dQ / dV diagrams (ef) for different number of cycles. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0034] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known structures, circuits, materials, or methods have not been specifically described in order to avoid obscuring the invention.

[0035] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0036] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0038] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0039] Currently, coating the surface of lithium-rich cathode materials with a coating layer through wet chemical coating reaction and secondary high-temperature calcination is one of the commonly used modification methods. However, this conventional coating method usually involves an additional subsequent calcination process, which not only increases the energy consumption in the material modification process, but also increases the corresponding time cost.

[0040] To solve the above technical problems:

[0041] In a first aspect, the present invention provides a germanium-doped lithium-rich manganese-based cathode material, comprising a germanium ion-doped lithium-rich manganese-based cathode material matrix and a fast ion conductor lithium germanate coating layer, wherein the fast ion conductor lithium germanate coating layer coats the outside of the germanium ion-doped lithium-rich manganese-based cathode material matrix to form a core-shell structure.

[0042] In one specific embodiment, the fast ion conductor lithium germanate of the coating layer is nanoscale.

[0043] The germanium-doped lithium-rich manganese-based cathode material of the present invention can induce Ni by introducing germanium ions into the crystal lattice. 2+ Oxidation occurs, enhancing the cationic order of the material; by coating the outside with a nanoscale fast-ion conductor lithium germanate coating, the interfacial side reactions of the electrode material can be effectively isolated, while accelerating lithium-ion transport, improving the structural stability of the battery material, and thus improving the battery cycle performance.

[0044] Secondly, this invention provides a method for preparing a germanium-doped lithium-rich manganese-based cathode material, wherein Ni... 0.25 Mn 0.75 The mixture of CO3 precursor, lithium source and germanium-doped source is prepared by one-step high-temperature calcination.

[0045] In a specific embodiment, the preparation method is as follows:

[0046] Ni was prepared by carbonate coprecipitation in a continuously stirred reactor. 0.25 Mn 0.75 CO3 precursor;

[0047] The above Ni 0.25 Mn 0.75 The CO3 precursor is thoroughly ground and uniformly mixed with the Li and germanium sources in the lithium source in a certain proportion.

[0048] The mixture was placed in a high-temperature calcination furnace and calcined in air atmosphere. After annealing, germanium-modified germanium-doped lithium-rich manganese-based cathode material was obtained.

[0049] In one specific embodiment, the lithium source is Li2CO3 or LiOH, and the germanium doping source is GeO2.

[0050] In a particular implementation, the Ni 0.25 Mn 0.75 The molar ratio of Li to GeO2 in the CO3 precursor and lithium source is 1:1.5:(0.01~0.05).

[0051] In one specific embodiment, the high-temperature calcination includes pre-calcination and high-temperature calcination. The pre-calcination temperature is 450–550°C and the calcination time is 4–6 h. The high-temperature calcination temperature is 800–900°C and the calcination time is 10–14 h. The calcination is carried out at a heating rate of 3–5°C / min.

[0052] This invention employs a one-step sintering method to simultaneously achieve germanium doping of lithium-rich cathode materials and nanoscale fast ion conductor lithium germanate coating. This eliminates the secondary calcination process in commonly used modification preparation methods for lithium-rich manganese-based cathode materials, reducing energy consumption and time costs in the preparation process and facilitating the industrial application and promotion of lithium-rich manganese-based cathode materials.

[0053] Thirdly, the present invention provides an application of germanium-doped lithium-rich manganese-based cathode material in lithium-ion batteries.

[0054] In a specific embodiment, the application method is as follows: the germanium-doped lithium-rich manganese-based cathode material is mixed with a conductive agent, a binder (PVDF) and a conductive agent (carbon black) in a mass ratio of 8:1:1, and uniformly coated on an aluminum foil. The coated electrode is then vacuum dried, and the prepared electrode is cut and weighed according to the battery assembly requirements.

[0055] In one specific implementation, the battery assembly uses a lithium sheet as the negative electrode, and the positive electrode sheet is assembled into a button cell in a glove box.

[0056] Fourthly, the present invention provides a lithium-ion battery comprising a positive electrode and a negative electrode, wherein the positive electrode is made of the germanium-doped lithium-rich manganese-based positive electrode material.

[0057] Example 1

[0058] The present invention provides a method for preparing a germanium-doped lithium-rich manganese-based cathode material, comprising the following steps:

[0059] Ni was prepared by carbonate coprecipitation in a continuously stirred reactor. 0.25 Mn0.75 A CO3 precursor was prepared by mixing the precursor, Li in lithium carbonate, and germanium dioxide (GeO2) in a molar ratio of 1:1.5:0.01. The mixture was thoroughly ground and homogeneously mixed, then placed in a high-temperature calcination furnace and calcined in air at a heating rate of 3–5 °C / min. The mixture was first pre-calcined at 500 °C for 5 h, followed by high-temperature calcination at 800 °C for 12 h. After annealing, germanium-modified germanium-doped lithium-rich manganese-based material G1 was obtained. The germanium-doped lithium-rich manganese-based material G1 was characterized by XRD, XPS, and TEM.

[0060] Example 2

[0061] The present invention provides a method for preparing a germanium-doped lithium-rich manganese-based cathode material, comprising the following steps:

[0062] Ni was prepared by carbonate coprecipitation in a continuously stirred reactor. 0.25 Mn 0.75 A CO3 precursor was prepared by mixing the precursor, Li in lithium carbonate, and germanium dioxide (GeO2) in a molar ratio of 1:1.5:0.02. The mixture was thoroughly ground and homogeneously mixed, then placed in a high-temperature calcination furnace and calcined in air at a heating rate of 3–5 °C / min. The mixture was first pre-calcined at 500 °C for 5 h, followed by high-temperature calcination at 800 °C for 12 h. After annealing, germanium-modified germanium-doped lithium-rich manganese-based material G2 was obtained. The germanium-doped lithium-rich manganese-based material G2 was characterized by XRD, XPS, and TEM.

[0063] Example 3

[0064] The present invention provides a method for preparing a germanium-doped lithium-rich manganese-based cathode material, comprising the following steps:

[0065] Ni was prepared by carbonate coprecipitation in a continuously stirred reactor. 0.25 Mn 0.75 A CO3 precursor was prepared by mixing the precursor, Li in lithium carbonate, and germanium dioxide (GeO2) in a molar ratio of 1:1.5:0.03. The mixture was thoroughly ground and homogeneously mixed, then placed in a high-temperature calcination furnace and calcined in air at a heating rate of 3–5 °C / min. The mixture was first pre-calcined at 500 °C for 5 h, followed by high-temperature calcination at 800 °C for 12 h. After annealing, germanium-modified germanium-doped lithium-rich manganese-based material G3 was obtained. The germanium-doped lithium-rich manganese-based material G3 was characterized by XRD, XPS, and TEM.

[0066] Comparative Example

[0067] The comparative example provides a method for preparing a germanium-doped lithium-rich manganese-based cathode material, comprising the following steps:

[0068] Ni was prepared by carbonate coprecipitation in a continuously stirred reactor. 0.25 Mn 0.75 A CO3 precursor was prepared by mixing the precursor and Li in lithium carbonate at a molar ratio of 1:1.5, grinding them thoroughly and mixing them uniformly. The mixture was then placed in a high-temperature calcination furnace and calcined in air at a heating rate of 3–5 °C / min. The furnace was first pre-calcined at 500 °C for 5 h, followed by high-temperature calcination at 800 °C for 12 h. After annealing, undoped lithium-rich manganese-based material G0 was obtained. The lithium-rich manganese-based material G0 was characterized by XRD, XPS, and TEM.

[0069] Battery assembly

[0070] Positive electrode sheets were prepared using the lithium-rich manganese-based materials obtained in Examples 1-3 and Comparative Example 1, respectively. The lithium-rich manganese-based materials, binder (PVDF), and conductive agent (carbon black) were dried and prepared for use. They were then homogenized at a mass ratio of 8:1:1 and uniformly coated onto aluminum foil. The coated electrode sheets were then vacuum dried. The prepared electrode sheets were cut and weighed according to battery assembly requirements. Using lithium foil as the negative electrode, coin cell half-cells were assembled using the positive electrode sheets in a glove box.

[0071] Constant current charge-discharge testing was performed with a voltage window of 2.0-4.8V and a capacitance of 250mAg. -1 The current was set to 1C, and the battery test temperature was 25℃.

[0072] Test Results

[0073] like Figure 2 As shown, the main XRD diffraction peaks of electrode materials G0, G1, G2, and G3 all belong to the layered hexagonal phase R-3m, and no diffraction peaks of heterogeneous phases were observed in any of the electrode materials. Notably, the weak diffraction peaks appearing at 20-22° are attributed to the unique LiMn6 superlattice in the transition metal layer of the lithium-rich cathode material, indicating the presence of a monoclinic phase C2 / m within all electrode materials, meaning the prepared lithium-rich material is a two-phase composite. Due to instrument detection limitations and insufficient lithium germanate coating loading, no XRD diffraction peaks corresponding to lithium germanate (Cmc21) crystals were found in the XRD spectra. Furthermore, the obvious splitting of the doublets 006 / 102 and 018 / 110 indicates that all electrode materials are well-crystallized layered structures. Figure 2 (b) is Figure 2 The magnified image of the 003 diffraction peak in (a) shows that as the amount of germanium ion doping increases, the 003 peak shifts slightly to a lower angle, indicating that during long-term high-temperature calcination, tetravalent germanium ions diffuse and migrate into the interior of the lithium-rich material lattice, thereby changing the lattice parameters of the material.

[0074] XPS with a depth of less than 20 nm was used for characterization to investigate the effect of germanium ion doping on the valence states of other transition metal elements in lithium-rich materials. Figure 3 (a) shows the XPS full spectrum of the G0, G1, G2 and G3 electrode materials. The XPS full spectrum can be used to find the XPS signals of the main elements Ni, Mn and O and the dopant element Ge. Figure 3 (bd) represents the fitting and analysis of the fine XPS spectra of each element. The XPS spectrum of Ni 2p is shown in... Figure 3 In (b), Ni 2p3 / 2 shifts to higher binding energy sites, indicating that the chemical valence state of surface Ni is affected by germanium ion doping. As the doping content increases (from 1 mol% to 3 mol%), the valence state of Ni 2p, representing Ni... 2+ The peak area at (855.18 eV) decreases, meaning that Ni 2+ The relative content of Ni gradually decreases, while the content of Ni that represents Ni decreases. 3+ The relative content of Ni (856.38 eV) gradually increases. After peak separation and semi-quantitative analysis of Ni 2p3 / 2 using software, the Ni content within the lithium-rich material was calculated. 2+ and Ni 3+ The relative content of Ni2+ is negatively correlated with the doping amount of germanium ions. The undoped G0 material Ni... 2+ The relative content of is 52.83%, while that of G3 material has dropped to 28.67%, indicating that the germanium ions introduced into the material lattice can induce Ni 2+ Oxidation occurs to generate Ni in a higher oxidation state. 3+ The modified material contains less Ni. 2+ This is beneficial for improving cation ordering and reducing cation mixing, and this analytical result is completely consistent with the XRD analysis results. The Mn 2p3 / 2 peak position in the modified material shows a slight tendency to shift towards lower binding energies, such as... Figure 3 As shown in (c), this is attributed to a portion of Mn 4+ Converted to Mn3 + To achieve charge balance within the material. The XPS spectrum of the doped element Ge 3d is shown in... Figure 3 (d) As the doping content increases, the relative intensity of the XPS signal representing the element Ge also increases, which is consistent with the experimental design of the change in germanium ion content.

[0075] Figure 4 (ae) shows the TEM high-resolution image and FFT images of different regions of the G0 electrode material. The surface and bulk regions of the G0 material exhibit identical and clearly visible lattice fringes, indicating the absence of other heterogeneous phases, consistent with XRD analysis. Secondly, the lattice fringes are marked in the magnified TEM image. Corresponding to the (111) crystal plane of the monoclinic C2 / m phase, the diffraction spots of C2 / m in the FFT image were further confirmed. After germanium ion modification, an epitaxial heterophase coating with a thickness of approximately 5 nm was present on the surface of the G2 material. The coating was uniform and tightly bonded to the host material. The lattice fringe spacing of the nanoscale epitaxial coating was [missing information]. By comparing the standard card with the (220) crystal plane of the Cmc21 phase lithium germanate (Li2GeO3), and the presence of diffraction spots corresponding to Cmc21 in its selected area FFT image, it was further confirmed that the uniform nanoscale coating on the surface is lithium germanate. The germanium-containing heterogeneous phase coating formed on the surface may be due to the reaction of some GeO2 with the lithium carbonate on the surface under high temperature calcination to form well-crystallized lithium germanate, and the coating is very uniform due to the presence of interfacial ion diffusion. This is consistent with the SEM analysis above, that is, the number of surface pores of germanium ion modified materials is significantly suppressed. The main region of the G2 material still exhibits a typical lithium-rich layered monoclinic phase C2 / m, in which The lattice fringes correspond to the (1-10) crystal plane of C2 / m. To investigate the distribution of germanium ions in the material, elemental mapping analysis of the G2 material was performed using TEM, such as... Figure 4 As shown in (ko), all elements such as Ni, Mn, Ge, and O are uniformly distributed on the surface of the material particles. Combined XRD, XPS, and TEM tests demonstrate the successful simultaneous realization of lattice germanium ion doping and a fast-ion conductor lithium germanate coating during lithiation.

[0076] The cycling performance of electrode materials G0, G1, G2, and G3 after 300 cycles is as follows: Figure 5 As shown in (a), the G0 material can release 202.29 mAh g at a current of 1C. -1 The initial discharge specific capacity was high, but only 46.52% of the initial capacity was retained at the end of the cycle, exhibiting rapid capacity decay. After modification with a germanium-containing heterophase coating, the long-term cycling stability of the materials was significantly improved. Under the same current density test, the capacity retention rates of materials G1, G2, and G3 were 88.57%, 92.26%, and 85.87%, respectively. In particular, material G2 was still able to release 180.87 mAh g⁻¹ at the end of the cycle. -1 The discharge specific capacity was determined. Since the material with a doping concentration of 2 mol% exhibited the best capacity retention among all modified samples, subsequent analysis will primarily focus on comparing the electrochemical performance of G0 and G2 electrode materials to explore the mechanism of germanium-containing heterophase coating doping. The average discharge voltage curves of G0 and G2 materials are shown below. Figure 5As shown in (b), after 300 cycles, the average voltage retention of the G0 material was only 76.83%, and its average discharge voltage had dropped below 3.0V by cycle 122. At the end of the cycle, its average voltage was 2.69V, indicating a severe crystal structure transformation (from layered to spinel) within the G0 material. Furthermore, with repeated charge and discharge cycles, the spinel structure formed on the material surface gradually spreads and diffuses into the material's interior, eventually forming a large number of inactive spinel structures, leading to voltage hysteresis and voltage decay. In contrast, the G2 material maintained an average voltage retention of 83.32% after 300 cycles, and its discharge voltage at the end of the cycle was higher than 3.0V (3.17V), indicating that the irreversible phase transition within the G2 material was significantly suppressed. Figure 5 (cd) shows the charge-discharge curves of G0 and G2 materials. The yellow curve represents the first charge-discharge cycle, consistent with the charging plateau characteristic of lithium-rich manganese-based substrate cathode materials, exhibiting a two-phase delithiation process. The specific capacity of G2 material is 10 mAh g⁻¹ lower than that of G0 material. This is because the lithium germanate coating on the surface of G2 material provides some resistance during the first charge cycle, preventing lithium ions from rapidly detaching from the lattice. The selected-cycle charge-discharge curves further verify that G0 material exhibits severe voltage decay (black arrow), while G2 material maintains a relatively stable discharge plateau, with its voltage decline trend greatly suppressed. The corresponding dQ / dV images are obtained after processing the charge-discharge curves, as shown below. Figure 5 As shown in (ef), the oxidation and reduction peaks of material G0 show significant shifts, indicating obvious voltage polarization during cycling. Furthermore, as the number of cycles increases, the reduction peak gradually shifts to the potential corresponding to the spinel phase structure, indicating a lattice transformation. In contrast, the oxidation and reduction peaks of material G2 show better overlap, with less internal voltage polarization. Although the reduction peak also tends to shift to lower potentials with cycling, it remains above 3.0V after 300 cycles. Therefore, this demonstrates that germanium-containing surface integration modification can enhance the material's stable reversibility and extend its cycle life.

[0077] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A germanium-doped lithium-rich manganese-based cathode material, characterized in that, It includes a germanium-doped lithium-rich manganese-based cathode material matrix and a fast-ion conductor lithium germanate coating layer, wherein the fast-ion conductor lithium germanate coating layer coats the outside of the germanium-doped lithium-rich manganese-based cathode material matrix to form a core-shell structure.

2. The germanium-doped lithium-rich manganese-based cathode material according to claim 1, characterized in that, The fast ion conductor lithium germanate in the coating layer is nanoscale.

3. The method for preparing the germanium-doped lithium-rich manganese-based cathode material according to claim 1 or 2, characterized in that, Ni 0.25 Mn 0.75 The mixture of CO3 precursor, lithium source and germanium-doped source is prepared by one-step high-temperature calcination.

4. The method for preparing germanium-doped lithium-rich manganese-based cathode material according to claim 3, characterized in that, The specific preparation method is as follows: Preparation of Ni 0.25 Mn 0.75 CO3 precursor; The above Ni 0.25 Mn 0.75 CO3 precursor is ground and uniformly mixed with lithium source and germanium source in a certain proportion; The mixture was placed in a high-temperature calcination furnace and calcined in air atmosphere. After annealing, germanium-doped lithium-rich manganese-based cathode material was obtained.

5. The method for preparing germanium-doped lithium-rich manganese-based cathode material according to claim 3, characterized in that, The lithium source is Li2CO3 or LiOH, and the germanium doping source is GeO2.

6. The method for preparing germanium-doped lithium-rich manganese-based cathode material according to claim 5, characterized in that, The Ni 0.25 Mn 0.75 The molar ratio of Li to GeO2 in the CO3 precursor and lithium source is 1:1.5:(0.01~0.05).

7. The method for preparing germanium-doped lithium-rich manganese-based cathode material according to claim 3, characterized in that, The high-temperature calcination includes pre-calcination and high-temperature calcination. The pre-calcination temperature is 450–550°C and the calcination time is 4–6 hours. The high-temperature calcination temperature is 800–900°C and the calcination time is 10–14 hours.

8. The application of the germanium-doped lithium-rich manganese-based cathode material according to claim 1 or 2, or the germanium-doped lithium-rich manganese-based cathode material prepared by any of the preparation methods according to claims 3 to 7, in lithium-ion batteries.

9. The application of the germanium-doped lithium-rich manganese-based cathode material according to claim 8 in lithium-ion batteries, characterized in that, The application method is as follows: the germanium-doped lithium-rich manganese-based cathode material is mixed with a conductive agent, a binder and a conductive agent, and uniformly coated on an aluminum foil. After drying, a cathode sheet is obtained, and then assembled into a lithium-ion battery.

10. A lithium-ion battery comprising a positive electrode and a negative electrode, characterized in that, The cathode is prepared using the germanium-doped lithium-rich manganese-based cathode material as described in claim 1 or 2, or the preparation method described in any one of claims 3 to 7.

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