Lithium supplementing material, preparation method thereof, positive electrode material and secondary battery

Abstract

The application discloses a lithium supplement material, a preparation method thereof, a positive electrode material and a secondary battery. The lithium supplement material comprises a transition metal lithium-rich material and a supporting material. The supporting material is compounded with the transition metal lithium-rich material, and the decomposition voltage of the supporting material is higher than the highest charging voltage of the transition metal lithium-rich material. The lithium supplement material has the advantages that the supporting material has a higher decomposition voltage, so after the transition metal lithium-rich material is charged to a certain voltage and decomposes a higher capacity, the supporting material can still exist in the lithium supplement material and stabilize the structure of the lithium supplement material, so as to inhibit the micro-cracks in the particles and the grains of the lithium supplement material in the charging process, and effectively improve the structural stability and the electrochemical performance of the lithium supplement material.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a lithium replenishment material and its preparation method, a cathode material, and a secondary battery. Background Technology

[0002] Rechargeable lithium-ion batteries (LIBs) are widely used in portable electronic devices and electric vehicles due to their long lifespan and high energy density. With the continued growth of the electric vehicle market, high-energy-density LIBs are increasingly used to extend range. However, traditional graphite anode LIBs consume active lithium to form a solid electrolyte interface (SEI), resulting in permanent lithium loss during the first cycle. This irreversible loss of active lithium inevitably reduces capacity and energy density, hindering the achievement of emerging high-energy-density requirements.

[0003] Lithium replenishment in the cathode involves adding an additional lithium source to the positive electrode active material. However, current lithium replenishment materials, after decomposing to a certain voltage and achieving a high capacity, experience significant volume shrinkage due to the deep delithiation, accompanied by the generation of large amounts of oxygen. This leads to numerous microcracks within the lithium replenishment material. These microcracks not only degrade the structural stability of the lithium replenishment material but also inhibit the transport of electrons and lithium ions through the particle-electrolyte interface, reducing electrical performance. Furthermore, electrolyte seeps into the cracks, resulting in unnecessary electrolyte waste. Therefore, preventing the formation of microcracks in lithium replenishment materials has become crucial. Summary of the Invention

[0004] The purpose of this invention is to provide a lithium replenishment material and its preparation method, a cathode material and a secondary battery, and to solve the problem of microcracks generated inside the lithium replenishment material.

[0005] To achieve the objectives of this application, the following technical solution is provided:

[0006] In a first aspect, the present invention provides a lithium replenishment material, comprising a transition metal lithium-rich material and a support material, wherein the support material is compounded with the transition metal lithium-rich material, and the decomposition voltage of the support material is higher than the maximum charging voltage of the transition metal lithium-rich material.

[0007] The lithium replenishment materials provided in this application include transition metal lithium-rich materials and support materials. Since the lithium replenishment effect of transition metal lithium-rich materials is mainly reflected in the upper limit of the first-cycle voltage, the upper limit of the voltage of general lithium-rich materials needs to be between 4.0-4.5V to meet the decomposition of active lithium. In addition to meeting the voltage window, sufficient conductivity support is also required. Since the decomposition voltage of the support material is higher than the maximum charging voltage of the transition metal lithium-rich material (the support material meets the window above 4.6V), and the decomposition voltage of the transition metal lithium-rich material does not overlap with that of the transition metal lithium-rich material, they will not affect each other. Furthermore, since the support material does not have sufficient conductivity support, it is difficult to decompose effectively in terms of kinetics. Therefore, the support material can serve as a support structure for the transition metal lithium-rich material.

[0008] In one embodiment, the content of the supporting material is less than that of the lithium-rich transition metal material, and the supporting material and the lithium-rich transition metal material form a solid solution.

[0009] In one embodiment, the transition metal lithium-rich material includes a plurality of primary grains, and the outer surface of the primary grains is connected to a plurality of supporting materials; the plurality of primary grains are connected through the supporting materials to form secondary grains.

[0010] In one embodiment, the mass ratio of the transition metal lithium-rich material to the support material is 100:(2.5~20).

[0011] In one embodiment, the supporting material and the lithium-rich transition metal material together form a core, and the lithium replenishment material further includes a passivation layer covering the outer surface of the core, the passivation layer comprising a metal oxide.

[0012] In one embodiment, the lithium replenishment material further includes a conductive layer covering the outer surface of the passivation layer, the conductive layer comprising a carbon material.

[0013] In one embodiment, the particle size D50 of the kernel is 1 μm to 15 μm.

[0014] In one embodiment, the thickness of the passivation layer is 0.5 nm to 10 nm.

[0015] In one embodiment, the thickness of the conductive layer is 10 nm to 150 nm.

[0016] In one embodiment, the mass ratio of the core, the passivation layer, and the conductive layer is (90~99):(0.01~0.5):(0.5~9).

[0017] Secondly, the present invention also provides a method for preparing a lithium replenishing material, comprising: mixing a lithium source, a transition metal source, and a supporting material precursor in a certain proportion to obtain a mixture; sintering the mixture under an inert atmosphere to obtain the lithium replenishing material; wherein the lithium replenishing material comprises a transition metal lithium-rich material and a supporting material, the supporting material being compounded with the transition metal lithium-rich material, and the decomposition voltage of the supporting material being higher than the maximum charging voltage of the transition metal lithium-rich material.

[0018] This application describes a lithium-rich material and a support material that can be prepared in one step by mixing and sintering a lithium source and a transition metal source. By controlling the mixing ratio and sintering parameters, the lithium-rich material and the support material together form a solid solution. In the lithium-rich material, the support material has a higher decomposition voltage. Therefore, after the lithium-rich material is charged to a certain voltage and decomposes to release a high capacity, the support material can still exist stably in the lithium-rich material and stabilize its structure. This suppresses microcracks in the particles and grains of the lithium-rich material during charging, effectively improving the structural stability and electrochemical performance of the lithium-rich material.

[0019] Thirdly, the present invention also provides a positive electrode material, the positive electrode material comprising a positive electrode active material and a lithium replenishing material, wherein the lithium replenishing material is the lithium replenishing material described in the first aspect, or the positive electrode material comprises a lithium replenishing material obtained by the preparation method of the lithium replenishing material described in the second aspect.

[0020] Fourthly, the present invention also provides a secondary battery, the secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, the separator being disposed between the positive electrode and the negative electrode, the positive electrode, the negative electrode, and the separator being immersed in the electrolyte, and the positive electrode comprising the positive electrode material described in the third aspect. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic cross-sectional view of a lithium supplement material according to one embodiment;

[0023] Figure 2 This is a cross-sectional schematic diagram of a lithium supplement material according to another embodiment;

[0024] Figure 3 This is a cross-sectional schematic diagram of a lithium replenishment material according to one embodiment, including a core, a passivation layer, and a conductive layer;

[0025] Figure 4 This is a flowchart illustrating a method for preparing a lithium-supplementing material according to one implementation.

[0026] Figure 5 This is a SEM (scanning electron microscope) image of a lithium supplement material with microcracks in one embodiment.

[0027] Figure 6 This is a magnified SEM (scanning electron microscope) image of microcracks on a lithium-filled material. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] It should be noted that when a component is said to be "fixed" to another component, it can be directly on the other component or it can be in a middle component. When a component is said to be "connected" to another component, it can be directly connected to the other component or it may be in a middle component.

[0030] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items.

[0031] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0032] The following are explanations of terms that appear in the text:

[0033] Solid solutions are alloy phases in which solute atoms dissolve into the solvent lattice while retaining the solvent's crystal structure. Generally, a solid solution is a crystal composed of atoms or molecules of other substances dissolved in a chemical matrix. Although solute atoms occupy some positions within the solvent lattice, the overall structure of the solid solution retains the solvent's crystal structure type. If the solvent's crystal structure can be stably maintained and homogeneous after the addition of a solute, such a mixture can be considered a solution.

[0034] This application provides a lithium supplement material; please refer to [reference needed]. Figure 1 The lithium supplement material includes a transition metal lithium-rich material 11 and a support material 12. The support material 12 is connected to the transition metal lithium-rich material 11, and the content of the support material 12 is less than that of the transition metal lithium-rich material 11. The support material 12 and the transition metal lithium-rich material 11 form a solid solution.

[0035] Specifically, the transition metal lithium-rich material 11 can be a lithium-rich transition metal-based lithium material, specifically composed of transition metal elements, lithium elements, and oxygen elements. The chemical formula of the transition metal lithium-rich material 11 can be Li. a N b O c Wherein, N is at least one of the transition metal elements such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, and Ru, and 1≤a≤8, 0<b, 0<c<7.

[0036] Optionally, the transition metal lithium-rich material 11 can also be a doped structure, with the chemical formula including Li. a N b1 M b2 O c Wherein, N is Fe and / or Co, M is at least one element selected from Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, V, Mo, Sn, 1≤a≤8, 0<b1+b2, b2<b1, 0<c<7.

[0037] In specific embodiments, the transition metal lithium-rich material 11 can be lithium-rich lithium iron ferrite (Li5FeO4), lithium-rich lithium cobalt oxide (Li6CoO4), or, the transition metal lithium-rich material 11 can be a lithium-rich iron-based material or a lithium-rich cobalt-based material, such as Li 4.985 Fe 0.967 Al 0.03 O 3.988 Li6Co 0.98 Ni 0.02 O4, Li8ZrO6. It needs to be explained that the above transition metal lithium-rich material 11 and the support material 12 have the same crystal phase, so the bonding effect between the two is the best. Therefore, the support material 12 and the transition metal lithium-rich material 11 are combined and form a solid solution.

[0038] Optionally, the support material 12 can be a lithium-containing support material, such as lithium oxide (Li2O) or lithium orthosilicate (Li4SiO4); in other embodiments, the support material 12 can also be a non-lithium support material, such as magnesium oxide. It should be explained that the support material 12 is a material with a high decomposition voltage, and the decomposition voltage is greater than the highest charging voltage of transition metal lithium-rich materials. Taking lithium oxide and lithium-rich lithium iron ferrite (Li5FeO4) as examples, in the prior art, the decomposition voltage of conventionally sized and unmodified lithium oxide is >4.7V; while the charging voltage of Li5FeO4 is approximately 2.5V~3.9V, and only the last lithium in Li5FeO4 is extracted at a voltage above 4.2V.

[0039] In the lithium supplementation material, the mass proportion of the support material 12 should be less than that of the transition metal lithium-rich material 11, and the transition metal lithium-rich material 11 and the support material 12 are formed simultaneously through the sintering of raw materials, rather than through simple solid-phase mixing, in order to form a stable solid solution. In a specific embodiment, by co-sintering the lithium source and the transition metal source, and by controlling the sintering temperature and time, a lithium supplementation material combining the transition metal lithium-rich material 11 and the support material 12 can be obtained.

[0040] Understandably, in lithium replenishment materials, the transition metal lithium-rich material 11 and the supporting material 12 together form a granular structure, which can be spherical, near-spherical, or other shapes. The transition metal lithium-rich material 11 acts as the "solvent" in the solid solution, and the supporting material 12 acts as the "solute" in the solid solution. Therefore, in lithium replenishment materials, the supporting material 12 can be distributed in a star-like pattern within the particles, such as... Figure 1 As shown.

[0041] The lithium replenishment material provided in this application includes a transition metal lithium-rich material 11 and a support material 12. Since the lithium replenishment effect of the transition metal lithium-rich material 11 is mainly reflected in the lithium replenishment capacity of the first cycle, the discharge voltage upper limit of general lithium-rich materials is between 4.0V and 4.5V to meet the decomposition of active lithium. In addition to meeting the voltage window, sufficient conductivity support is also required. Since the decomposition voltage of the support material 12 is higher than the maximum charging voltage of the transition metal lithium-rich material 11 (the support material 12 meets the decomposition voltage above 4.6V), and the decomposition voltage of the transition metal lithium-rich material 11 does not overlap, they will not affect each other. Furthermore, since the support material 12 is made of a material with relatively weak conductivity, it is difficult to decompose effectively in terms of kinetics. Therefore, the support material 12 can serve as a support structure for the transition metal lithium-rich material 11.

[0042] Furthermore, the transition metal lithium-rich material 11 and the support material 12 together form a solid solution, with the transition metal lithium-rich material 11 acting as the "solvent" and the support material 12 acting as the "solute". The advantage of this structure is that the support material 12 has a higher decomposition voltage. Therefore, after the transition metal lithium-rich material 11 is charged to a certain voltage and decomposes to release a higher capacity, the support material 12 can still exist stably in the lithium replenishment material and stabilize the structure of the lithium replenishment material. This suppresses microcracks in the lithium replenishment material particles and grains during the charging process, effectively improving the structural stability and electrochemical performance of the lithium replenishment material.

[0043] In one implementation method, please refer to Figure 1 The transition metal lithium-rich material 11 includes multiple primary grains, which are connected by a support material 12 to form secondary grains.

[0044] Specifically, the transition metal lithium-rich material 11 and the supporting material 12 together constitute the secondary grains. It should be explained that the lithium-replenishing materials provided by this invention all exist in a particulate structure within the positive electrode, and the positive electrode contains multiple lithium-replenishing material particles. The number of lithium-replenishing material particles in the positive electrode is not limited, and each lithium-replenishing material particle is a secondary grain, which is a particle formed by the aggregation or agglomeration of multiple primary grains.

[0045] Optionally, the primary grains can be spherical or near-spherical, or other irregular shapes, preferably spherical. Therefore, the secondary grains formed by connecting multiple primary grains can be spherical or near-spherical, or other irregular shapes, without any specific limitation.

[0046] It is understandable that after cleaning the lithium replenishment material from the positive electrode, multiple secondary grains are obtained. These secondary grains can be further broken down into primary grains through crushing or other methods. Therefore, the primary grain is the smallest particulate unit that makes up the secondary grains, and the secondary grain is the smallest unit used in this invention to assemble the positive electrode.

[0047] The transition metal lithium-rich material 11 includes multiple primary grains, and the support material 12 may also include multiple primary grains. The primary grains of the transition metal lithium-rich material 11 and the primary grains of the support material 12 are mixed together to form a solid solution. Furthermore, the mixing of multiple primary grains (including the primary grains of the transition metal lithium-rich material 11 and the primary grains of the support material 12) forms secondary grains, so the secondary grains can have a garnet-like structure, such as... Figure 1 As shown, in the cross-section of the secondary grains of the lithium replenishment material, A represents the primary grain of the transition metal lithium-rich material 11, and B represents the primary grain of the support material 12.

[0048] Understandably, during the delithiation process of the transition metal lithium-rich material 11, the diffusion of transition metal ions leads to an increase in the number of vacant Li sites, accompanied by changes in lattice constant and volume, as well as oxygen release from the lattice, resulting in thermal and structural instability. Secondly, the primary grains of the transition metal lithium-rich material 11 have different crystallographic orientations and slip planes. During lithium-ion intercalation / deintercalation, due to anisotropy, lattice volume expansion, contraction, and intercalation occur between grains, leading to microcracks (such as...) in the grains. Figure 5 and Figure 6 As shown, microcracks become new reaction sites with the electrolyte, leading to the disruption of conductive pathways between grains. The disruption of conductive pathways and the instability caused by heat generation from material decomposition lead to the degradation of the electrochemical performance of the cathode material, thereby reducing the battery's electrical performance. Therefore, the support material 12, placed between multiple primary grains, can suppress the crystallographic orientation and slip planes between adjacent primary grains, thus preventing the electrolyte from causing electrical disconnection between grains, thereby ensuring the electrochemical performance of the lithium replenishment material.

[0049] In one implementation method, please refer to Figure 1 The outer surface of the primary grain is connected to a plurality of supporting material 12 grains, and there is a spacing between the plurality of supporting material 12 grains.

[0050] Specifically, based on the above embodiments, the outer surface of the primary grains of the transition metal lithium-rich material 11 can be connected to multiple ring-shaped distributed grains of support material 12. For example... Figure 1 As shown, the primary grains of the transition metal lithium-rich material 11 have a larger grain size, thus having a larger surface area to connect the grains of multiple support materials 12. On the same primary grain of the transition metal lithium-rich material 11, the grains of two adjacent support materials 12 have a spacing distance.

[0051] In one implementation method, please refer to Figure 2 The outer surface of the primary grain is connected to multiple grains of support material 12, and the multiple grains of support material 12 are connected to form a surface film of support material 12.

[0052] Specifically, based on the above embodiments, the outer surface of the primary grains of the transition metal lithium-rich material 11 can be connected to multiple grains of support material 12 to form a surface film. For example... Figure 2 As shown, on the primary grains of the same transition metal lithium-rich material 11, the grains of two adjacent support materials 12 are connected, thereby forming a surface film of the support material 12 by connecting the grains of multiple support materials 12.

[0053] Optionally, the surface film of the support material 12 can cover part of the outer surface of the primary grains of the transition metal lithium-rich material 11.

[0054] In one embodiment, the support material 12 forms a continuous three-dimensional skeleton structure, and the transition metal lithium-rich material 11 is connected to the three-dimensional skeleton structure.

[0055] Specifically, based on the above-described embodiment, gaps are formed between the primary grains of the plurality of transition metal lithium-rich materials 11, and the support material 12 fills these gaps. Since the lithium replenishment material can contain multiple primary grains of transition metal lithium-rich materials 11, the gaps formed between the primary grains of the plurality of transition metal lithium-rich materials 11 can be continuous, that is, the support material 12 filling the gaps is also continuous.

[0056] In one embodiment, the mass ratio of the transition metal lithium-rich material 11 to the support material 12 is 100:(2.5~20). Optionally, the mass ratio of the transition metal lithium-rich material 11 to the support material 12 can be 100:2.5, 100:5, 100:7.5, 100:10, 100:12.5, 100:15, 100:17.5, or 100:20.

[0057] Maintaining the mass ratio of the transition metal lithium-rich material 11 to the support material 12 within the aforementioned range not only ensures the stability of the support material 12 in the structure of the transition metal lithium-rich material 11 and prevents microcracks, but also avoids increasing the decomposition voltage of the lithium replenishment material. If the mass ratio of the support material 12 is too low, its effect on stabilizing the structure of the transition metal lithium-rich material 11 will be poor, and cracks will still appear in the lithium replenishment material. If the mass ratio of the support material 12 is too high, the composition of the lithium replenishment material will contain a large amount of support material 12, and since the decomposition voltage of the support material 12 is higher than that of the transition metal lithium-rich material 11, the lithium replenishment material will only be able to release lithium ions at a higher voltage, which will also increase the gas production of the material.

[0058] In one implementation method, please refer to Figure 3 The core 10 is composed of the support material 12 and the transition metal lithium-rich material 11. The lithium supplementation material also includes a passivation layer 20, which covers the outer surface of the core 10 and includes a metal oxide.

[0059] Specifically, the support material 12 and the transition metal lithium-rich material 11 can jointly form the core 10. The core 10 can contain multiple secondary particles of the transition metal lithium-rich material 11, and the outer surface of each secondary particle can be coated with the support material 12, such as... Figure 3 As shown, the core 10 is the main structure that provides lithium ions to the lithium replenishment material. The passivation layer 20 covers the outer surface of the core 10, meaning that the passivation layer 20 can be connected to the support material 12.

[0060] The passivation layer 20 is mainly composed of metal oxides, and the metal elements in the metal oxides can be one or more of Al, Ti, Fe, Ca, Zn, Cu, Ba, and Cr. Optionally, the passivation layer 20 is prepared by atomic layer deposition technology, so the thickness of the passivation layer 20 is relatively thin. The purpose of setting the passivation layer 20 is to: 1) effectively prevent the core 10 interface from reacting with water and carbon dioxide in the environment, resulting in the formation of excessive residual alkali, and maintain the structural stability and performance stability of the core 10; 2) the passivation layer 20 has high density, which can prevent external moisture from corroding the core 10 and improve the moisture resistance and processing performance of the lithium replenishment material; 3) the nanoscale metal oxide has high catalytic ability and can catalyze the release of lithium ions from the core 10 at a lower voltage.

[0061] In one embodiment, the particle size D50 of the core 10 is 1 μm to 15 μm. Optionally, the particle size D50 of the core 10 can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm.

[0062] If the particle size D50 of the core 10 is within the above range, it not only has a good lithium replenishment effect, but also facilitates the combination of the lithium replenishment material and the positive electrode active material, further improving its lithium replenishment effect.

[0063] In one embodiment, the thickness of the passivation layer 20 is 0.5 nm to 10 nm. Optionally, the thickness of the passivation layer 20 can be 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, or 10 nm.

[0064] The thickness of the passivation layer 20 is within the aforementioned range, which effectively prevents the formation of residual alkali, maintains the structural and performance stability of the core 10, and has little impact on carrier migration and transport. If the thickness of the passivation layer 20 is too high, it will affect the utilization of active components and lithium efficiency in the core 10; if the thickness of the passivation layer 20 is too low, it will be detrimental to improving the structural and performance stability of the core 10.

[0065] In one implementation method, please refer to Figure 3 The lithium replenishment material also includes a conductive layer 30, which is coated on the outer surface of the core 10 and includes a carbon material.

[0066] Specifically, the outer surface layer of the core 10 also includes a conductive layer 30. The conductive layer 30 can be directly coated on the outer surface of the core 10, or it can be coated on the outer surface of the passivation layer 20 mentioned above. The main material of the conductive layer 30 is carbon, including at least one of graphene, carbon nanotubes, conductive carbon black, and conductive graphite. These carbon materials all have good conductivity and can effectively improve the electron transport efficiency of the lithium-ion material.

[0067] In one embodiment, the thickness of the conductive layer 30 is 10nm to 150nm. Optionally, the thickness of the conductive layer 30 can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, or 150nm.

[0068] Ensuring the thickness of the conductive layer 30 is within the aforementioned range effectively improves electron transport efficiency. If the thickness of the conductive layer 30 is too high, it will affect the utilization of the active components and lithium efficiency in the core 10; if the thickness of the conductive layer 30 is too low, it will hinder the improvement of the overall conductivity of the lithium replenishment material.

[0069] In one embodiment, the mass ratio of the core 10, the passivation layer 20, and the conductive layer 30 is (90~99):(0.01~0.5):(0.5~9). Optionally, the mass ratio of the core 10, the passivation layer 20, and the conductive layer 30 can be 90:(0.01~0.5):(0.5~9), 93:(0.01~0.5):(0.5~9), 96:(0.01~0.5):(0.5~9), 99:(0.01~0.5):(0.5~9), (90~99):0.01:(0.5~9), (90~99):0.05:(0.5~9), (90~99):0.05:(0.5~9), (90~99):0.01 ...9):0.01:(0.5~9), (90~999):0.01:(0.5~9), (90~999):0.01:(0.5~9), (90~999):0.01:(0.5~9), (90~999):0.01:(0.5~9), (90~999):0.01:(0.5~9), (90~999):0.01 9):0.1:(0.5~9)(90~99):0.3:(0.5~9)(90~99):0.5:(0.5~9)(90~99):(0.01~0.5):0.5,(90~99):(0.01~0.5):1,(90~99):(0.01~0.5):3,(90~99):(0.01~0.5):6,(90~99):(0.01~0.5):9。

[0070] Maintaining the mass ratio of core 10, passivation layer 20, and conductive layer 30 within the aforementioned range effectively prevents the formation of residual alkali, maintains the structural and performance stability of core 10, and has minimal impact on carrier migration and transport; it also effectively improves electron transport efficiency. If the mass ratio of passivation layer 20 or conductive layer 30 is too high, it reduces the content of transition metal lithium-rich material 11 and support material 12 in the lithium replenishment material, thereby affecting the lithium replenishment effect; if the mass ratio of passivation layer 20 or conductive layer 30 is too low, it cannot achieve the passivation effect, or its effect on improving the conductivity of the lithium replenishment material is limited.

[0071] In one embodiment, the present invention also provides a method for preparing a lithium-supplementing material, please refer to [reference needed]. Figure 4 Specifically, it includes the following steps:

[0072] Step S10: Mix the lithium source, transition metal source and support material precursor in a certain proportion to obtain a mixture.

[0073] Step S20: The mixture is sintered under an inert atmosphere to obtain a lithium supplement material.

[0074] Among them, the lithium replenishment material includes transition metal lithium-rich material and support material. The support material is compounded with the transition metal lithium-rich material, and the decomposition voltage of the support material is higher than the maximum charging voltage of the transition metal lithium-rich material.

[0075] Optionally, in step S10, the lithium source includes at least one of lithium nitrate, lithium carbonate, lithium acetate, lithium oxalate, lithium borate, lithium phosphate, lithium chloride, hydrogen support material, oversupport material, and support material.

[0076] Optionally, in step S10, the transition metal source includes an iron source and / or a cobalt source, specifically including but not limited to iron hydroxide, iron oxide, iron nitrate, cobalt oxide, cobalt hydroxide, cobalt carbonate, etc.

[0077] Optionally, in step S10, when the support material is lithium oxide, the support material precursor can be the same material as the transition metal source. When the support material is magnesium oxide or lithium orthosilicate, the support material precursor can be magnesium oxide or silicon dioxide, etc.

[0078] Optionally, in step S20, the sintering conditions of the mixture can be 600℃~900℃, and the sintering time can be 1h~6h.

[0079] In one embodiment, the method for preparing the lithium-supplementing material further includes fabricating a passivation layer and a conductive layer; please refer to [reference needed]. Figure 4 Specifically, it includes the following steps:

[0080] Step S30: A transition metal lithium-rich material and a support material are used as the core, and a passivation layer is formed on the outer surface of the core. The passivation layer includes a metal oxide.

[0081] Step S40: A conductive layer is formed on the outer surface of the passivation layer. The conductive layer includes a carbon material.

[0082] Optionally, in step S30, a dense passivation layer can be formed on the outer surface of the core using atomic layer deposition technology, and the metal element in the metal oxide can be one or more of Al, Ti, Fe, Ca, Zn, Cu, Ba, and Cr.

[0083] Optionally, in step S40, the material obtained after step S30 can be mixed with carbon material by high-speed ball milling in a certain proportion, and the carbon material includes at least one of graphene, carbon nanotubes, conductive carbon black, and conductive graphite.

[0084] This application describes a lithium-rich material and a support material that can be prepared in one step by mixing and sintering a lithium source and a transition metal source. By controlling the mixing ratio and sintering parameters, the lithium-rich material and the support material together form a solid solution. In the lithium-rich material, the support material has a higher decomposition voltage. Therefore, even if a phase change occurs during the delithiation process after the lithium-rich material is charged to a certain voltage and decomposes to release lithium ions, the support material can still exist stably in the lithium-rich material and help stabilize the structure of the lithium-rich material. This helps to suppress microcracks in the particles and grains of the lithium-rich material during charging, effectively improving the structural stability and electrochemical performance of the lithium-rich material.

[0085] In one embodiment, the present invention also provides a cathode material, which includes a cathode active material and a lithium replenishment material. The lithium replenishment material includes the lithium replenishment material provided in the above embodiments. Optionally, the cathode active material can be a phosphate cathode active material and a ternary cathode active material. In specific embodiments, it includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, lithium fluorinated vanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0086] In one embodiment, the content of the lithium replenishing material in the cathode material can be controlled at 1% to 6% of the mass of the cathode active material. This ratio can precisely compensate for the loss of active lithium during the first charge of the battery. If the amount of lithium replenishing material added to the cathode material is too low, the lost active lithium in the cathode active material cannot be fully replenished, which is not conducive to improving the energy density and capacity retention of the battery. If the amount of lithium replenishing material added to the cathode active material is too high, it will occupy the original reversible capacity and increase the cost. In some specific embodiments, the mass percentage of the lithium replenishing material in the cathode material can be 1%, 2%, 4%, 6%, etc.

[0087] In one embodiment, the present invention also provides a positive electrode sheet, the positive electrode sheet comprising a current collector and an active material layer disposed on the current collector, the active material layer comprising the lithium-supplementing material of any of the above embodiments. Alternatively, the active material layer comprises a lithium-supplementing material obtained by the preparation method of the lithium-supplementing material in the above embodiments.

[0088] In one embodiment, the positive electrode sheet includes a positive current collector, and a positive active layer is formed on the positive current collector. The positive active layer includes components such as a positive active material, a lithium supplementation material, a conductive agent, and a binder. This invention does not specifically limit these materials; suitable materials can be selected according to actual application requirements. The positive current collector includes, but is not limited to, any one of copper foil and aluminum foil. The conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes, and the content of the conductive agent in the positive active layer is 3wt% to 5wt%. The binder includes one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives, and the content of the binder in the positive active layer is 2wt% to 4wt%.

[0089] In one embodiment, the present invention also provides a secondary battery, the secondary battery comprising a negative electrode, a separator, and a positive electrode as described above. The positive electrode comprises the aforementioned composite positive electrode material.

[0090] The technical solution of the present invention will be described in detail below through specific embodiments.

[0091] Example 1

[0092] This embodiment provides a lithium supplementation material, including a core, a passivation layer, and a conductive layer; wherein, the core includes a lithium-rich iron-based material (Li5FeO4) and a support material (Li2O), the passivation layer includes aluminum oxide (Al2O3), and the conductive layer includes conductive carbon black.

[0093] The mass ratio of Li5FeO4 to Li2O is 97:3; the core particle size is 8 μm; the passivation layer thickness is 30 nm; the conductive layer thickness is 100 nm; and the mass ratio of the core, passivation layer, and conductive layer is 97:0.05:2.95.

[0094] The method for preparing the lithium supplementation material provided in this embodiment is as follows:

[0095] (1) Lithium source LiOH and transition metal source Fe2O3 are mixed evenly in proportion to obtain a mixture. The mixture is placed under an inert atmosphere and sintered at 700-900℃ for 10-20h and then crushed to obtain the core.

[0096] (2) Place the core powder in an atomic layer deposition device and set an Al2O3 passivation layer on the core surface after 5-30 cycles.

[0097] (3) The core with the passivation layer is fused with the carbon source at high speed to form a conductive carbon layer on the surface of the passivation layer.

[0098] Example 2

[0099] This embodiment provides a lithium supplementation material, including a core, a passivation layer, and a conductive layer; wherein, the core includes a lithium-rich iron-based material (Li5FeO4) and a support material (Li2O), the passivation layer includes aluminum oxide (Al2O3), and the conductive layer includes conductive carbon black.

[0100] The mass ratio of Li5FeO4 to Li2O is 98.5:1.5; the core particle size is 8 μm; the passivation layer thickness is 30 nm; the conductive layer thickness is 100 nm; and the mass ratio of the core, passivation layer, and conductive layer is 97:0.05:2.95.

[0101] The difference between this embodiment and Embodiment 1 is that the mass ratio of Li5FeMO4 to Li2O is 98.5:1.5.

[0102] Example 3

[0103] This embodiment provides a lithium supplementation material, including a core, a passivation layer, and a conductive layer; wherein, the core includes a lithium-rich iron-based material (Li5FeO4) and a support material (Li2O), the passivation layer includes aluminum oxide (Al2O3), and the conductive layer includes conductive carbon black.

[0104] The mass ratio of Li5FeO4 to Li2O is 94:6; the core particle size is 8 μm; the passivation layer thickness is 30 nm; the conductive layer thickness is 100 nm; and the mass ratio of the core, passivation layer, and conductive layer is 97:0.05:2.95.

[0105] The difference between this embodiment and Embodiment 1 is that the mass ratio of Li5FeO4 to Li2O is 94:6.

[0106] Example 4

[0107] This embodiment provides a lithium supplement material, including a core, a passivation layer, and a conductive layer; wherein, the core includes a lithium-rich cobalt-based material (Li6CoO4) and a support material (Li2O), the passivation layer includes aluminum oxide (Al2O3), and the conductive layer includes conductive carbon black.

[0108] The mass ratio of Li6CoO4 to Li2O is 97:3; the core particle size is 8 μm; the passivation layer thickness is 30 nm; the conductive layer thickness is 100 nm; and the mass ratio of the core, passivation layer, and conductive layer is 97:0.05:2.95.

[0109] The difference between this embodiment and Embodiment 1 is that the core includes a lithium-rich cobalt-based material (Li6CoO4) and a supporting material (Li2O).

[0110] Example 5

[0111] This embodiment provides a lithium replenishment material, including a core, a passivation layer, and a conductive layer; wherein, the core includes a lithium-rich iron-based material (Li). 4.985 Fe 0.967 Al 0.03 O 3.988 The material consists of a support material (Li2O), a passivation layer comprising aluminum oxide (Al2O3), and a conductive layer comprising conductive carbon black.

[0112] Li 4.985 Fe 0.967 Al 0.03 O 3.988 The mass ratio of the core to Li₂O is 97:3; the particle size of the core is 8 μm; the thickness of the passivation layer is 30 nm; the thickness of the conductive layer is 100 nm; and the mass ratio of the core, passivation layer and conductive layer is 97:0.05:2.95.

[0113] The difference between this embodiment and Embodiment 1 is that the lithium-rich iron-based material has Al doping. In the preparation method of this embodiment, step (1) involves mixing the lithium source LiOH and the transition metal sources Fe2O3 and Al2O3 in a certain proportion to obtain a mixture.

[0114] Example 6

[0115] This embodiment provides a lithium replenishment material, including a core, a passivation layer, and a conductive layer; wherein, the core includes a lithium-rich iron-based material (Li). 4.985 Fe 0.967 Ti 0.03 O 3.988 The material consists of a support material (Li2O), a passivation layer comprising aluminum oxide (Al2O3), and a conductive layer comprising conductive carbon black.

[0116] Li 4.985 Fe 0.967 Ti 0.03 O 3.988 The mass ratio of the core to Li₂O is 97:3; the particle size of the core is 8 μm; the thickness of the passivation layer is 30 nm; the thickness of the conductive layer is 100 nm; and the mass ratio of the core, passivation layer and conductive layer is 97:0.05:2.95.

[0117] The difference between this embodiment and Embodiment 1 is that the lithium-rich iron-based material has Ti doping. In the preparation method of this embodiment, step (1) involves mixing the lithium source LiOH and the transition metal sources Fe2O3 and TiO2 in a certain proportion to obtain a mixture.

[0118] Example 7

[0119] This embodiment provides a lithium supplementation material, including a core, a passivation layer, and a conductive layer; wherein, the core includes a lithium-rich iron-based material (Li5FeO4) and a support material (MgO), the passivation layer includes aluminum oxide (Al2O3), and the conductive layer includes conductive carbon black.

[0120] The mass ratio of Li5FeO4 to MgO is 97:3; the core particle size is 8 μm; the passivation layer thickness is 30 nm; the conductive layer thickness is 100 nm; and the mass ratio of the core, passivation layer, and conductive layer is 97:0.05:2.95.

[0121] The difference between this embodiment and Embodiment 1 is that the supporting material is MgO.

[0122] Example 8

[0123] This embodiment provides a lithium supplementation material, including a core, a passivation layer, and a conductive layer; wherein, the core includes a lithium-rich iron-based material (Li5FeO4) and a support material (Li4SiO4), the passivation layer includes aluminum oxide (Al2O3), and the conductive layer includes conductive carbon black.

[0124] The mass ratio of Li5FeO4 to Li4SiO4 is 97:3; the core particle size is 8 μm; the passivation layer thickness is 30 nm; the conductive layer thickness is 100 nm; and the mass ratio of the core, passivation layer, and conductive layer is 97:0.05:2.95.

[0125] The method for preparing the lithium supplementation material provided in this embodiment is as follows:

[0126] (1) Lithium source LiOH and transition metal source Fe2O3 and SiO2 are mixed evenly in proportion to obtain a mixture. The mixture is placed under an inert atmosphere and sintered at 700-900℃ for 10-20h and then crushed to obtain the core.

[0127] (2) Place the core powder in an atomic layer deposition device and set an Al2O3 passivation layer on the core surface after 5-30 cycles.

[0128] (3) The core with the passivation layer is fused with the carbon source at high speed to form a conductive carbon layer on the surface of the passivation layer.

[0129] Comparative Example 1

[0130] This comparative example provides a lithium supplementation material, including a core, a passivation layer, and a conductive layer; wherein the core includes a lithium-rich iron-based material (Li5FeO4), the passivation layer includes aluminum oxide (Al2O3), and the conductive layer includes conductive carbon black.

[0131] The core has a particle size of 8 μm; the passivation layer has a thickness of 30 nm; the conductive layer has a thickness of 100 nm; and the mass ratio of the core, passivation layer, and conductive layer is 97:0.05:2.95.

[0132] Comparative Example 2

[0133] This comparative example provides a lithium supplementation material, including a core, a passivation layer, and a conductive layer; wherein the core includes a lithium-rich iron-based material (Li5FeO4) and a support material (Li2O), the passivation layer includes aluminum oxide (Al2O3), and the conductive layer includes conductive carbon black.

[0134] The mass ratio of Li5FeO4 to Li2O is 97:3; the core particle size is 8 μm; the passivation layer thickness is 30 nm; the conductive layer thickness is 100 nm; and the mass ratio of the core, passivation layer, and conductive layer is 97:0.05:2.95.

[0135] The difference between this comparative example and Example 1 is that Li5FeO4 and Li2O are simply mixed and no solid solution is formed between them.

[0136] The lithium replenishment materials provided in Examples 1-7 and Comparative Examples 1-2 were assembled into positive electrode sheets and lithium-ion batteries respectively according to the following methods:

[0137] Positive electrode sheet: (active material LFP, lithium supplementing material), SP and PVDF are mixed and homogenized in a mass ratio of 95 (97:3):23:3 to form a positive electrode slurry. The positive electrode slurry is coated on the surface of aluminum foil, vacuum dried at 110°C overnight, and rolled to obtain a positive electrode sheet.

[0138] Negative electrode sheet: Graphite negative electrode;

[0139] Electrolyte: Ethyl carbonate and ethyl methyl carbonate are mixed in a volume ratio of 3:7, and LiPF6 is added to form an electrolyte with a concentration of 1 mol / L.

[0140] Diaphragm: Polypropylene microporous diaphragm;

[0141] Lithium-ion battery assembly: Assemble button-type lithium-ion full cells in an inert atmosphere glove box according to the assembly sequence of negative electrode plate-separator-electrolyte-positive electrode plate.

[0142] The electrochemical performance of each lithium-ion battery assembled in the above lithium-ion battery examples was tested under the following conditions:

[0143] The material was charged at a rate of 0.1C with a cutoff voltage of 4.2V. After the cutoff voltage reached 4.2V, constant voltage charging was performed. Following the charging process, the material was allowed to stand for 10 minutes before being discharged at a rate of 0.1C with a cutoff voltage of 2.5V. The charging plateau was observed during the charging process to obtain the delithiation voltage of the lithium-replenishing material. Subsequently, the material was cycled 300 times at 55℃ to test the cycle retention rate.

[0144] Resistivity testing: The resistivity of the positive electrode lithium replenishment material in each embodiment and comparative example was obtained by testing and calculation using the four-probe method.

[0145] The test results of the above-mentioned lithium replenishment materials and lithium batteries are shown in Table 1 below:

[0146] Table 1. Test results of the examples and comparative examples

[0147]

[0148] From the test results of Examples 1-7 and Comparative Examples 1-2 in Table 1, it can be seen that the cycle retention rate of the lithium replenishment materials prepared in the examples is higher than that of the comparative examples. This indicates that the lithium replenishment material provided by the present invention can maintain a relatively stable structure after multiple charge-discharge cycles. This is because the lithium replenishment material contains a high-voltage supporting material (lithium oxide and magnesium oxide). The supporting material serves as the supporting structure for the lithium-rich material, thereby preventing cracks or structural collapse in the lithium replenishment material. Figure 5 The appearance of the conventional lithium-filling material in the comparative example is shown, with denser microcracks, larger microcrack widths, and longer microcrack lengths; among them... Figure 6 The appearance of the lithium replenishing material in the embodiments is shown, with narrower and shorter microcracks and shallower microcrack textures. This indicates that the lithium replenishing material provided by the present invention has fewer microcracks.

[0149] As can be seen from the test results of Examples 1-3 in Table 1, the cycle retention rate of the lithium replenishment material is higher as the proportion of the supporting material increases. However, since the supporting material does not release lithium ions under the voltage of the lithium-rich material, the initial charge capacity of the lithium-rich material is affected.

[0150] The test results of Examples 1 and 4-6 in Table 1 show that the solution provided by the present invention is also applicable to other lithium-rich materials (cobalt-based) and other doped lithium-rich materials, indicating that the solution provided by the present invention has universality.

[0151] As can be seen from the test results of Examples 1, 7 and 8 in Table 1, the solution provided by the present invention can also use other supporting materials (such as Li4SiO4 and MgO), indicating that the specific type of supporting material in the solution provided by the present invention is not limited. It can be a lithium-containing supporting material or a non-lithium supporting material. However, lithium-containing supporting materials have similar crystal structures to lithium-rich materials and have better effects.

[0152] In summary, since the decomposition voltage of the supporting material is higher than the maximum charging voltage of the transition metal lithium-rich material, the decomposition voltages of the supporting material and the transition metal lithium-rich material do not overlap and will not affect each other. Therefore, the supporting material is kinetically difficult to decompose effectively when the transition metal lithium-rich material is discharged. The supporting material can serve as a supporting structure for the transition metal lithium-rich material, thereby preventing the collapse of the lithium replenishment material structure and improving the cycle stability of the lithium replenishment material.

[0153] In the description of the embodiments of this application, it should be noted that the orientation or positional relationship of the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and other indicators are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0154] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art will understand that all or part of the processes for implementing the above embodiments and equivalent variations made in accordance with the claims of this application are still within the scope of this application.

Claims

1. A lithium supplementation material, characterized in that, It includes a transition metal lithium-rich material and a support material, wherein the support material is compounded with the transition metal lithium-rich material, and the support material serves as a support structure for the transition metal lithium-rich material, and the decomposition voltage of the support material is higher than the maximum charging voltage of the transition metal lithium-rich material; The transition metal lithium-rich material is composed of transition metal elements, lithium elements and oxygen elements, and the supporting material is one of lithium oxide, lithium orthosilicate and magnesium oxide. The chemical formula of the transition metal lithium-rich material is Li. a Fe b1 M b2 O c Wherein, M is at least one element selected from Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, V, Mo, Sn, 1≤a≤8, 0<b1+b2, b2<b1, 0<c<7, and the lithium replenishing material is used for lithium replenishment; The supporting material forms a continuous three-dimensional framework structure, and the lithium-rich transition metal material is connected to the three-dimensional framework structure; the lithium-rich transition metal material includes a plurality of primary grains, and the outer surface of the primary grains is connected to a plurality of the supporting material; the plurality of primary grains are connected through the supporting material to form secondary grains; the supporting material and the lithium-rich transition metal material form a solid solution.

2. The lithium replenishment material according to claim 1, characterized in that, The content of the supporting material is less than that of the lithium-rich transition metal material.

3. The lithium replenishment material according to claim 1, characterized in that, The mass ratio of the lithium-rich transition metal material to the supporting material is 100:(2.5~20).

4. The lithium replenishment material according to claim 1, characterized in that, The supporting material and the lithium-rich transition metal material together form the core, and the lithium replenishment material also includes a passivation layer covering the outer surface of the core, the passivation layer comprising a metal oxide.

5. The lithium replenishment material according to claim 4, characterized in that, The lithium replenishment material also includes a conductive layer covering the outer surface of the passivation layer, the conductive layer comprising a carbon material.

6. The lithium replenishment material according to claim 5, characterized in that, The kernel's particle size D50 is 1μm~15μm; and / or The passivation layer has a thickness of 0.5 nm to 10 nm; and / or The thickness of the conductive layer is 10nm~150nm; and / or The mass ratio of the core, the passivation layer, and the conductive layer is (90~99):(0.01~0.5):(0.5~9).

7. A method for preparing a lithium-supplementing material, characterized in that, include: A mixture is obtained by mixing lithium source, transition metal source and support material precursor in a certain proportion; The mixture was sintered under an inert atmosphere to obtain the lithium supplement material; The lithium replenishment material comprises a transition metal lithium-rich material and a supporting material. The supporting material is compounded with the transition metal lithium-rich material, serving as a supporting structure for the transition metal lithium-rich material. The decomposition voltage of the supporting material is higher than the maximum charging voltage of the transition metal lithium-rich material. The transition metal lithium-rich material is composed of a transition metal element, lithium element, and oxygen element. The supporting material is one of lithium oxide, lithium orthosilicate, and magnesium oxide. The chemical formula of the transition metal lithium-rich material is Li. a Fe b1 M b2 O c Wherein, M is at least one element selected from Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, V, Mo, and Sn, 1≤a≤8, 0<b1+b2, b2<b1, 0<c<7, and the lithium replenishing material is used for lithium replenishment; the supporting material forms a continuous three-dimensional framework structure, and the transition metal lithium-rich material is connected to the three-dimensional framework structure; the transition metal lithium-rich material includes multiple primary grains, and multiple supporting materials are connected to the outer surface of the primary grains; the multiple primary grains are connected through the supporting materials to form secondary grains, and the supporting material and the transition metal lithium-rich material form a solid solution.

8. A positive electrode material, characterized in that, The cathode material includes an active material and a lithium replenishing material, wherein the lithium replenishing material is the lithium replenishing material as described in any one of claims 1-6, or the cathode material includes the lithium replenishing material obtained by the preparation method of the lithium replenishing material as described in claim 7.

9. A secondary battery, characterized in that, The device includes a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is disposed between the positive electrode and the negative electrode. The positive electrode, the negative electrode, and the separator are immersed in the electrolyte. The positive electrode includes the positive electrode material as described in claim 8.

Images