Lithium ferrite pre-lithiation additive, positive electrode material, positive electrode sheet, and secondary battery
By forming a core-shell structure on the surface of lithium ferrite supplement, and controlling the ID/IG ratio and shell thickness, the problem of poor air stability of lithium ferrite supplement is solved, achieving high-capacity and long-life lithium-ion battery performance.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- HUBEI WANRUN NEW ENERGY TECH CO LTD
- Filing Date
- 2025-01-15
- Publication Date
- 2026-07-09
Smart Images
Figure CN2025072447_09072026_PF_FP_ABST
Abstract
Description
A lithium ferrite lithium supplement, a positive electrode material, a positive electrode sheet, and a secondary battery. Technical Field
[0001] This invention relates to the field of secondary battery technology, specifically to a lithium iron phosphate lithium replenisher, a positive electrode material, a positive electrode sheet, and a secondary battery. Background Technology
[0002] During the first charge of a lithium-ion battery, approximately 15% of the active lithium ions participate in the formation of the solid electrolyte interphase (SEI) film, leading to reversible lithium loss at the positive electrode and consequently reducing the battery's capacity. To address the lithium loss problem during the first charge of lithium-ion batteries, the industry typically employs pre-lithiation by adding lithium replenishing agents to the positive electrode material. To date, researchers have explored various lithium replenishing agents for positive electrode pre-lithiation, including Li₂NiO₂, Li₂O₂, Li₂C₄O₄, Li₂S, Li₃N, Li₆CoO₄, and Li₅FeO₄ (LFO). However, integrating binary compounds such as Li₂O₂, Li₂O₂, Li₂C₄O₄, Li₂S, and Li₃N as lithium replenishing agents into current battery manufacturing technologies faces significant challenges. The main issues are their incompatibility with existing electrode fabrication systems and their high cost. In contrast, ternary compounds such as Li₂NiO₂, Li₂C₄O₄, Li₆CoO₄, and LFO offer better safety, stability, and compatibility.
[0003] Among them, light-treated volatile organic compounds (LFOs) stand out due to their abundant raw material resources, high theoretical capacity (867 mAh / g), and industrialization potential. However, LFOs exhibit extremely poor air stability, with their specific capacity rapidly decreasing upon contact with air. To address these technical issues, researchers have improved the air stability of LFOs to some extent by coating them with Li6CoO4, doping them with zirconium, or using polyethylene oxide-polypropylene oxide-polyethylene copolymer as a carbon coating. However, the capacity retention rate of LFOs modified by these methods after 24 hours of exposure to air is difficult to reach 80%, and their long-term stability in air still needs improvement. Summary of the Invention
[0004] In view of the technical problems existing in the background art, this application provides a lithium iron ferrite lithium replenishing agent, a positive electrode material, a positive electrode sheet and a secondary battery, aiming to solve the technical problem of poor air stability of existing lithium iron ferrite lithium replenishing agents.
[0005] In a first aspect, embodiments of this application provide a lithium ferrite lithium supplement agent, which includes a core layer and a shell layer covering the surface of the core layer. The core layer is made of Li5FeO4, and the shell layer is made of carbon material. The lithium ferrite lithium supplement agent has I D / IG The value is 1.0 to 1.2, and the average thickness of the shell is 60 nm to 200 nm.
[0006] In the technical solution of this application embodiment, by forming a core-shell structure and controlling the average thickness of the shell layer, the shell layer can, to a certain extent, prevent the Li5FeO4 in the core layer from contacting the air. Further, I D / I G The ratio of the intensity of peak D to peak G in the Raman spectrum, where peak D is at 1350 cm⁻¹. -1 Nearby peaks, used to characterize defects, with the G peak at 1580 cm⁻¹. -1 Nearby peaks, used to characterize the degree of graphitization, I D / I G The larger the value, the more defects are indicated. In this application, the lithium ferrite supplement is adjusted by I... D / I G Controlling these defects helps to create a suitable number of defects in the shell, promoting the adsorption of H2O and CO2 from the air, thereby improving the air stability of lithium ferrite supplements.
[0007] In some embodiments, the free radical concentration of the lithium ferrite supplement is 1.2 × 10⁻⁶. 13 spins / g ~ 1.8 × 10⁻⁶ 13 spins / g.
[0008] In this application, by controlling the free radical concentration of the lithium ferrite supplement within the above-mentioned range, the resulting lithium ferrite supplement exhibits excellent air stability.
[0009] In some embodiments, the mass fraction of carbon in the lithium ferrite supplement is 2% to 5%.
[0010] In this embodiment, by controlling the mass fraction of carbon, it helps to form a uniform and dense shell, further improving the air stability of lithium ferrite supplement. On the other hand, it helps to improve the conductivity of lithium ferrite supplement and increase the lithium-ion migration rate. When applied to the cathode material, it can participate in the formation of the SEI film before the cathode active material during the first charge and discharge process, thereby improving the reversible capacity of the cathode material.
[0011] In some embodiments, the D50 particle size of the lithium ferrite supplement is 3 μm to 6 μm.
[0012] In this embodiment, by controlling the D50 particle size of the lithium ferrite supplement, the specific surface area of the lithium ferrite supplement can be increased, enabling the shell material to form good bonding with H2O and CO2 in the air and inhibiting its further reaction with the core material Li5FeO4. On the other hand, the lithium ferrite supplement can be more easily dispersed, forming a uniform positive electrode material with the positive electrode active material. Furthermore, its electron transport rate and ion transport rate can be improved, thereby improving the electrochemical performance of the formed positive electrode material.
[0013] In some embodiments, the lithium ferrite supplement has a specific capacity greater than 570 mAh / g after exposure to air at 25°C and 20% relative humidity for 24 h; and / or, the lithium ferrite supplement has a specific capacity greater than 530 mAh / g after exposure to air at 25°C and 20% relative humidity for 48 h; and / or, the lithium ferrite supplement has a specific capacity greater than 520 mAh / g after exposure to air at 25°C and 20% relative humidity for 72 h.
[0014] The lithium ferrite supplement provided in this application has excellent specific capacity and air stability. When the lithium ferrite supplement is used to prepare cathode materials, it helps to improve the specific capacity of the prepared cathode materials, and thus helps to improve the electrochemical performance of secondary batteries prepared using the cathode materials. In other words, it can improve the commercialization of lithium ferrite supplement in the field of secondary batteries.
[0015] In some embodiments, the capacity retention rate of the lithium ferrite supplement after exposure to air at 25°C and 20% relative humidity for 24 hours is greater than 88%; and / or, the capacity retention rate of the lithium ferrite supplement after exposure to air at 25°C and 20% relative humidity for 48 hours is greater than 82%; and / or, the capacity retention rate of the lithium ferrite supplement after exposure to air at 25°C and 20% relative humidity for 72 hours is greater than 80%.
[0016] The lithium ferrite supplement provided in this application has excellent air stability, making it suitable for long-term storage and beneficial for improving the cycle stability of secondary batteries prepared using this lithium ferrite supplement. At the same time, the capacity retention rate of the lithium ferrite supplement can still be maintained at a high level after being exposed to air for a period of time, which is beneficial for improving the electrochemical performance of secondary batteries prepared using this lithium ferrite supplement.
[0017] Secondly, embodiments of this application provide a positive electrode material, which includes a positive electrode active material, a conductive agent, a binder, and a lithium replenishing agent, wherein the lithium replenishing agent is the lithium ferrite lithium replenishing agent of the first aspect of this application.
[0018] In the technical solution of this application embodiment, the specific capacity of the prepared cathode material can be effectively improved by using the lithium ferrite lithium supplement agent in the above embodiment.
[0019] In some embodiments, the mass ratio of lithium supplement to positive electrode active material is (1:100) to (5:100).
[0020] In this embodiment, if the amount of lithium replenishing agent added is too small, the number of lithium ions replenished will be too small, and the lithium replenishing effect of the lithium replenishing agent will be poor; while if the amount of lithium replenishing agent added is too large, it will affect the electrochemical performance of the cathode material.
[0021] In some embodiments, the cathode material described in this application retains more than 93% of its capacity after 100 cycles at a 0.33C rate.
[0022] In this embodiment, the cathode material prepared using lithium ferrite as a lithium supplement exhibits good cycle performance and high capacity retention, which is beneficial for improving the cycle stability of the secondary battery prepared using this cathode material and can extend the service life of the secondary battery, thereby broadening the application range of the prepared secondary battery.
[0023] Thirdly, embodiments of this application provide a positive electrode sheet, including a current collector and a positive electrode material located on one or both sides of the current collector, wherein the positive electrode material is the positive electrode material of the second aspect of this application.
[0024] In this embodiment, the positive electrode sheet contains the aforementioned positive electrode material, thus exhibiting high capacity retention.
[0025] Fourthly, embodiments of this application provide a secondary battery, including a positive electrode, a negative electrode, and a separator, wherein the positive electrode is the positive electrode of the third aspect of this application.
[0026] In this embodiment, the secondary battery includes the aforementioned positive electrode sheet, thus possessing the advantages of high energy density and good cycle performance.
[0027] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description
[0028] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.
[0029] Figure 1 is a TEM image of the lithium ferrite lithium supplement in Example 1;
[0030] Figure 2 shows the Raman spectra of the lithium ferrite supplements in Example 1 and Comparative Example 1;
[0031] Figure 3 shows the SEM images of the lithium ferrite supplement in Example 1 and Comparative Example 1.
[0032] Figure 4 shows the XRD patterns of the lithium ferrite supplements in Example 1 and Comparative Example 1 after being placed in air at 25°C and 20% relative humidity for different times.
[0033] Figure 5 shows the GITT test results of the lithium ferrite supplements in Example 1 and Comparative Example 1.
[0034] Figure 6 shows the specific capacity data of the lithium ferrite supplement in Example 1 and Comparative Example 1 after being placed in air at 25°C and 20% relative humidity for different times.
[0035] Figure 7 shows the specific capacity data of the lithium ferrite lithium supplement in Example 1 after being placed at 25°C under different humidity conditions for different times.
[0036] Figure 8 shows the rate performance test results of the lithium ferrite supplement in Example 1 and Comparative Example 1.
[0037] Figure 9 shows the rate performance and cycle performance of the positive electrode in half-cells in Example 8 and Comparative Example 5.
[0038] Figure 10 shows the rate performance test results of the secondary batteries in Example 9 and Comparative Example 6.
[0039] Figure 11 shows the cycle performance test results of the secondary batteries in Example 9 and Comparative Example 6 at 0.5C. Detailed Implementation
[0040] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.
[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.
[0042] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.
[0043] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.
[0044] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.
[0045] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).
[0046] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of 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. Therefore, they should not be construed as limitations on the embodiments of this application.
[0047] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.
[0048] Lithium loss occurs during the initial charge and discharge of lithium-ion batteries. Currently, pre-lithiation is commonly achieved by adding lithium replenishing agents to the cathode material to improve battery capacity. LFO stands out among many lithium replenishing agents due to its abundant raw material resources, high theoretical capacity (867 mAh / g), and industrialization potential. Its charging and discharging voltage windows are compatible with commercial cathode materials, and its production process perfectly matches existing lithium-ion battery manufacturing processes. Despite these numerous advantages, LFO's extremely poor air stability hinders its commercialization. Carbon atoms in CO2 from the air can bind to oxygen active sites on the LFO surface, with an adsorption energy of -0.3963 eV. Oxygen atoms in CO2 can attach to metal ion sites through Coulombic interactions, with an adsorption energy of -0.5160 eV. These data indicate that CO2 mainly forms adsorption on the LFO surface through carbon atoms. When H2O from the air is adsorbed onto the LFO surface, hydrogen atoms in H2O form hydrogen bonds with the surface active oxygen, with an adsorption energy of -0.2951 eV. Oxygen atoms in H2O are adsorbed to metal ion sites through Coulombic interactions, with an adsorption energy of -0.9155 eV. These data indicate that hydrogen atoms in H2O mainly form hydrogen bonds with the surface active oxygen of LFO. From the above data, it can be seen that LFO has a strong adsorption effect on both H2O and CO2. LFO is more likely to react with H2O in the air, leading to instability upon exposure.
[0049] To address the aforementioned technical problem of poor air stability of LFO, in a first aspect, embodiments of this application provide a lithium ferrite lithium replenisher. This lithium ferrite lithium replenisher includes a core layer and a shell layer covering the surface of the core layer. The core layer is made of Li5FeO4, and the shell layer is made of carbon material. The lithium ferrite lithium replenisher has I D / I G The value is 1.0 to 1.2. Specifically, it can be 1.0, 1.1, 1.2, etc., or other values within this range. No special limitation is made here. The average thickness of the shell is 60nm to 200nm. Specifically, it can be 60nm, 100nm, 200nm, etc., or other values within this range. No special limitation is made here.
[0050] In this application, I D / I G The ratio of the intensity of peak D to peak G in the Raman spectrum, where peak D is at 1350 cm⁻¹. -1 Nearby peaks, used to characterize defects, with the G peak at 1580 cm⁻¹. -1 Nearby peaks, used to characterize the degree of graphitization, I D / I G The larger the value, the more defects it indicates. This application addresses this by coating the Li5FeO4 core layer with a carbon-containing shell and then... D / I GBy controlling the thickness of the shell, the lithium iron ferrite supplement can form a good adsorption relationship with H2O and CO2 in the air, preventing them from reacting further with Li5FeO4 in the core layer. In addition, by controlling the average thickness of the shell, it is helpful to further reduce the probability of H2O and CO2 in the air entering the core layer, thereby improving the air stability of the lithium iron ferrite supplement.
[0051] Furthermore, in some embodiments, the free radical concentration of the lithium ferrite supplement is 1.2 × 10⁻⁶. 13 spins / g ~ 1.8 × 10⁻⁶ 13 spins / g, specifically, can be 1.2 × 10⁻⁶. 13 spins / g, 1.4×10 13 spins / g, 1.8×10 13 spins / g, etc., can also be other values within this range, without special restrictions here.
[0052] In this application, the air stability of lithium ferrite supplement is significantly improved by controlling the free radical concentration of the lithium ferrite supplement.
[0053] Furthermore, in some embodiments, the mass fraction of carbon in the lithium ferrite supplement is 2% to 5%, specifically, it can be 2%, 3%, 4%, 5%, etc., or other values within this range, without any special limitation.
[0054] In this application, controlling the mass fraction of carbon within the aforementioned range helps to form a uniform and dense shell, thereby effectively preventing the shell material from contacting air and improving the air stability of the lithium ferrite supplement. Furthermore, controlling the mass fraction of carbon within the aforementioned range helps to improve the conductivity of the lithium ferrite supplement and increase the lithium-ion migration rate. Moreover, when the mass fraction of carbon is within the aforementioned range, the lithium-ion migration rate is fast, which is beneficial for improving the reversible lithium capacity of the cathode material.
[0055] Furthermore, in some embodiments, the D50 particle size of the lithium ferrite supplement is 3μm to 6μm. Specifically, it can be 3μm, 4μm, 5μm, 6μm, etc., or other values within this range, without any special limitation.
[0056] In this application, the particle size of the lithium ferrite supplement has a certain impact on its dispersion performance and effective specific surface area. Controlling the D50 particle size of the lithium ferrite supplement within the above-mentioned range can, on the one hand, improve its dispersibility, which is beneficial for forming a uniform positive electrode material with the positive electrode active material; on the other hand, it helps to promote the adsorption of H2O and CO2 in the air by the shell material in the lithium ferrite supplement, further improving the air stability of the lithium ferrite supplement; and on the other hand, it helps to increase the contact area between the lithium ferrite supplement and the electrolyte, forming an SEI film and increasing the migration rate of lithium ions in the positive electrode material, so that the prepared secondary battery has good electrochemical performance.
[0057] Furthermore, in some embodiments, the specific capacity of the lithium ferrite supplement after exposure to air at 25°C and 20% relative humidity for 24 hours is greater than 570 mAh / g; and / or, the specific capacity of the lithium ferrite supplement after exposure to air at 25°C and 20% relative humidity for 48 hours is greater than 530 mAh / g; and / or, the specific capacity of the lithium ferrite supplement after exposure to air at 25°C and 20% relative humidity for 72 hours is greater than 520 mAh / g.
[0058] The lithium ferrite supplement provided in this application has excellent specific capacity and air stability. When the lithium ferrite supplement is used to prepare cathode materials, it helps to improve the specific capacity of the prepared cathode materials, and thus helps to improve the electrochemical performance of secondary batteries prepared using the cathode materials. In other words, it can improve the commercialization of lithium ferrite supplement in the field of secondary batteries.
[0059] Furthermore, in some embodiments, the capacity retention rate of the lithium ferrite supplement after exposure to air at 25°C and 20% relative humidity for 24 hours is above 88%; and / or, the capacity retention rate of the lithium ferrite supplement after exposure to air at 25°C and 20% relative humidity for 48 hours is above 82%; and / or, the capacity retention rate of the lithium ferrite supplement after exposure to air at 25°C and 20% relative humidity for 72 hours is above 80%.
[0060] It should be noted that the electrode preparation process before electrochemical performance testing, including mixing, coating, and slicing, was carried out in air at 25°C and 20% relative humidity. The capacity retention rates mentioned above are based on the performance of freshly prepared lithium ferrite electrode.
[0061] The lithium ferrite supplement provided in this application has excellent air stability, making it suitable for long-term storage and beneficial for improving the cycle stability of secondary batteries prepared using this lithium ferrite supplement. At the same time, the capacity retention rate of the lithium ferrite supplement can still be maintained at a high level after being exposed to air for a period of time, which is beneficial for improving the electrochemical performance of secondary batteries prepared using this lithium ferrite supplement.
[0062] A typical, but not limiting, method for preparing lithium ferrite supplements involves coating a carbon layer onto the surface of Li5FeO4. Specifically, Li5FeO4 can be mixed with asphalt and calcined. The calcination process is optimized to prepare a lithium ferrite supplement with a carbon shell coating on the core layer of Li5FeO4. Li5FeO4 can be obtained by purchasing or self-preparation. In particular, a two-stage calcination process is used: first, pre-calcination at 200℃–300℃ for 0.5–1.5 h, followed by calcination at 600℃–800℃ for 1–4 h, preferably calcination at 600℃–800℃ for 1–3 h, to obtain the lithium ferrite supplement. During the preparation process, the mass ratio of lithium ferrite supplement to asphalt is controlled to be (100:5)–(100:15). The prepared lithium ferrite supplement has a specific I... D / I G Within the range of 1.0 to 1.2, the average thickness of the shell layer of the lithium ferrite supplement is 60 nm to 200 nm. Therefore, the prepared lithium ferrite supplement has excellent air stability.
[0063] Secondly, embodiments of this application provide a positive electrode material, which includes a positive electrode active material, a conductive agent, a binder, and a lithium replenishing agent, wherein the lithium replenishing agent is a lithium ferrite lithium replenishing agent of the first aspect of this application, and the mass ratio of the lithium replenishing agent to the positive electrode active material is (1:100) to (5:100).
[0064] In this embodiment, controlling the amount of lithium replenishing agent has several advantages. First, it allows the lithium replenishing agent to replace the positive electrode active material in the formation of the SEI film, reducing reversible lithium loss in the positive electrode active material and increasing the specific capacity of the positive electrode material. Second, controlling the amount of lithium replenishing agent within the aforementioned range helps ensure the stability of the positive and negative electrode material structures during cycling, improving the battery's cycle life. If the amount of lithium replenishing agent is too small, the number of lithium ions replenished will be insufficient, resulting in poor lithium replenishment. Conversely, if the amount of lithium replenishing agent is too large, it will negatively impact the electrochemical performance of the positive electrode material.
[0065] Typical, but not limiting, positive electrode active materials include at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and lithium nickel cobalt manganese oxide; conductive agents include at least one of carbon black, conductive carbon black, graphite, graphene, acetylene black, and Ketjen black; and binders include at least one of polyvinyl alcohol, carboxymethyl cellulose, and polyacrylic acid.
[0066] Furthermore, in some embodiments, the cathode material described in this application retains more than 93% of its capacity after 100 cycles at a 0.33C rate.
[0067] In this application, by adding the lithium ferrite supplement agent described in the first aspect of this application to the cathode material, the cycle stability of the cathode material can be improved to a certain extent, which is conducive to improving the cycle performance of the secondary battery and broadening the application field of the secondary battery.
[0068] Thirdly, embodiments of this application provide a positive electrode sheet, including a current collector and a positive electrode material located on one or both sides of the current collector, wherein the positive electrode material is the positive electrode material of the second aspect of this application.
[0069] Due to the use of the aforementioned cathode material, this cathode sheet exhibits good stability and electrochemical performance.
[0070] Fourthly, embodiments of this application provide a secondary battery including the positive electrode sheet of the third aspect of this application, which has excellent energy density and cycle stability.
[0071] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.
[0072] I. Preparation Method
[0073] Lithium ferrite supplement
[0074] Example 1
[0075] One embodiment of the lithium ferrite lithium supplement agent of this application is prepared by the following method:
[0076] S1, Nano Fe2O3 and nano Li2O are mixed at a molar ratio of 1:5 to obtain the first mixture;
[0077] S2, the first mixture was placed in a tube furnace and sintered at 700°C under an argon atmosphere for 24 hours to obtain Li5FeO4;
[0078] S3, crush Li5FeO4 to a particle size of 1-10μm, and mix the crushed Li5FeO4 with asphalt at a mass ratio of 100:8 to obtain a second mixture;
[0079] S4. The second mixture is added to a tube furnace and calcined under an argon atmosphere. The temperature is first raised to 200°C and held for 1 hour, then raised to 700°C and held for 2 hours to obtain lithium ferrite supplement.
[0080] Example 2
[0081] One embodiment of the lithium ferrite lithium supplement agent of this application is prepared by the following method:
[0082] S1, Nano Fe2O3 and nano Li2O are mixed at a molar ratio of 1:5 to obtain the first mixture;
[0083] S2, the first mixture was placed in a tube furnace and sintered at 700°C under an argon atmosphere for 24 hours to obtain Li5FeO4;
[0084] S3, crush Li5FeO4 to a particle size of 1-10μm, and mix the crushed Li5FeO4 with asphalt at a mass ratio of 100:12 to obtain a second mixture;
[0085] S4. The second mixture is added to a tube furnace and calcined under an argon atmosphere. The temperature is first raised to 300°C and held for 0.5 hours, then raised to 800°C and held for 1 hour to obtain lithium ferrite supplement.
[0086] Example 3
[0087] One embodiment of the lithium ferrite lithium supplement agent of this application is prepared by the following method:
[0088] S1, Nano Fe2O3 and nano Li2O are mixed at a molar ratio of 1:5 to obtain the first mixture;
[0089] S2, the first mixture was placed in a tube furnace and sintered at 700°C under an argon atmosphere for 24 hours to obtain Li5FeO4;
[0090] S3, crush Li5FeO4 to a particle size of 1-10μm, and mix the crushed Li5FeO4 with asphalt at a mass ratio of 100:12 to obtain a second mixture;
[0091] S4. The second mixture is added to a tube furnace and calcined under an argon atmosphere. The temperature is first raised to 250°C and held for 1.5 hours, then raised to 600°C and held for 3 hours to obtain lithium ferrite supplement.
[0092] Example 4
[0093] One embodiment of the lithium ferrite lithium supplement agent of this application is prepared by the following method:
[0094] S1, Nano Fe2O3 and nano Li2O are mixed at a molar ratio of 1:5 to obtain the first mixture;
[0095] S2, the first mixture was placed in a tube furnace and sintered at 700°C under an argon atmosphere for 24 hours to obtain Li5FeO4;
[0096] S3, crush Li5FeO4 to a particle size of 1-10μm, and mix the crushed Li5FeO4 with asphalt at a mass ratio of 100:15 to obtain a second mixture;
[0097] S4. The second mixture is added to a tube furnace and calcined under an argon atmosphere. The temperature is first raised to 200°C and held for 1 hour, then raised to 700°C and held for 2 hours to obtain lithium ferrite supplement.
[0098] Example 5
[0099] One embodiment of the lithium ferrite lithium supplement agent of this application is prepared by the following method:
[0100] S1, Nano Fe2O3 and nano Li2O are mixed at a molar ratio of 1:5 to obtain the first mixture;
[0101] S2, the first mixture was placed in a tube furnace and sintered at 700°C under an argon atmosphere for 24 hours to obtain Li5FeO4;
[0102] S3, crush Li5FeO4 to a particle size of 1-10μm, and mix the crushed Li5FeO4 with asphalt at a mass ratio of 100:5 to obtain a second mixture;
[0103] S4. The second mixture is added to a tube furnace and calcined under an argon atmosphere. The temperature is first raised to 200°C and held for 1 hour, then raised to 700°C and held for 2 hours to obtain lithium ferrite supplement.
[0104] Example 6
[0105] One embodiment of the lithium ferrite lithium supplement agent of this application is prepared by the following method:
[0106] S1, Nano Fe2O3 and nano Li2O are mixed at a molar ratio of 1:5 to obtain the first mixture;
[0107] S2, the first mixture was placed in a tube furnace and sintered at 700°C under an argon atmosphere for 24 hours to obtain Li5FeO4;
[0108] S3, crush Li5FeO4 to a particle size of 1-10μm, and mix the crushed Li5FeO4 with asphalt at a mass ratio of 100:8 to obtain a second mixture;
[0109] S4. The second mixture is added to a tube furnace and calcined under an argon atmosphere. The temperature is first raised to 200°C and held for 1 hour, then raised to 700°C and held for 4 hours to obtain lithium ferrite supplement.
[0110] Example 7
[0111] One embodiment of the lithium ferrite lithium supplement agent of this application is prepared by the following method:
[0112] S1, Nano Fe2O3 and nano Li2O are mixed at a molar ratio of 1:5 to obtain the first mixture;
[0113] S2, the first mixture was placed in a tube furnace and sintered at 700°C under an argon atmosphere for 24 hours to obtain Li5FeO4;
[0114] S3, crush Li5FeO4 to a particle size of 1-10μm, and mix the crushed Li5FeO4 with asphalt at a mass ratio of 100:8 to obtain a second mixture;
[0115] S4. The second mixture is added to a tube furnace and calcined under an argon atmosphere. The temperature is first raised to 200°C and held for 1 hour, then raised to 500°C and held for 4 hours to obtain lithium ferrite supplement.
[0116] Comparative Example 1
[0117] A lithium ferrite lithium supplement is prepared in a method that differs from that in Example 1 only in that it does not include S3 and S4. The Li5FeO4 in S2 is pulverized to a particle size of 1-10 μm to obtain the lithium ferrite lithium supplement.
[0118] Comparative Example 2
[0119] A lithium ferrite lithium supplement is prepared in a method that differs from that in Example 1 only in that, in S3, the mass ratio of Li5FeO4 to asphalt is 100:3.
[0120] Comparative Example 3
[0121] A lithium ferrite supplement is prepared in a method that differs from that in Example 1 only in that, in step S4, the second mixture is added to a tube furnace and calcined under an argon atmosphere. The temperature is first raised to 200°C and held for 1 hour, and then raised to 700°C and held for 5 hours to obtain the lithium ferrite supplement.
[0122] Comparative Example 4
[0123] A lithium ferrite supplement is prepared in a method that differs from that in Example 1 only in that, in step S4, the second mixture is added to a tube furnace and calcined under an argon atmosphere, with the temperature directly raised to 700°C and held for 2.5 hours to obtain the lithium ferrite supplement.
[0124] [Cathode Materials]
[0125] Example 8
[0126] One embodiment of the cathode material of this application is prepared by the following method: NCM811, lithium ferrite lithium supplement, conductive carbon black and polyvinylidene fluoride are mixed in a mass ratio of 93.5:4:1:1.5 to prepare the cathode material. The lithium ferrite lithium supplement is the lithium ferrite lithium supplement prepared in Example 1.
[0127] Subsequently, using N-methylpyrrolidone as a solvent, the positive electrode material was mixed with the solvent to prepare a positive electrode slurry, which was then coated onto aluminum foil. The coating amount of the positive electrode active material was 75 mg / cm³. 2 This yields the positive electrode sheet.
[0128] Comparative Example 5
[0129] One embodiment of the cathode material of this application is prepared by the following method: NCM811, conductive carbon black and polyvinylidene fluoride are mixed in a mass ratio of 97.5:1:1.5 to obtain the cathode material.
[0130] Subsequently, using N-methylpyrrolidone as a solvent, the positive electrode material was mixed with the solvent to prepare a positive electrode slurry, which was then coated onto aluminum foil. The coating amount of the positive electrode active material was 75 mg / cm³. 2 This yields the positive electrode sheet.
[0131] Rechargeable batteries
[0132] Example 9
[0133] One embodiment of the secondary battery of this application involves using the positive electrode sheet prepared in Example 8 and SiO2. x A full cell is formed by a composite negative electrode composed of graphite (mass ratio of 1:8). The electrolyte uses LiPF6 as the lithium salt with a concentration of 1 mol / L, and the solvent is a compound solvent of ethylene carbonate and dimethyl carbonate with a mass ratio of 3:7.
[0134] Comparative Example 6
[0135] One embodiment of the secondary battery of this application uses a positive electrode sheet made of Comparative Example 5 and an electrode sheet made of SiO2. x A full cell is formed by a composite negative electrode composed of graphite (mass ratio of 1:8). The electrolyte uses LiPF6 as the lithium salt with a concentration of 1 mol / L, and the solvent is a compound solvent of ethylene carbonate and dimethyl carbonate with a mass ratio of 3:7.
[0136] II. Testing Methods
[0137] 1. Property testing of lithium ferrite supplement
[0138] (1)I D / I G: Obtained by Raman spectroscopy (HORIBA XploRA Nano spectrometer), with an excitation wavelength of 633 nm;
[0139] (2) Average thickness of the shell: obtained by transmission electron microscopy (TEM, FEI-Talos F200S);
[0140] (3) Surface morphology: tested by scanning electron microscopy (SEM, TESCAN MIRA LMS);
[0141] (4) Free radical concentration: measured by electron paramagnetic resonance (EPR, Bruker-EmxPlus);
[0142] (5) Mass fraction of carbon: tested by infrared carbon-sulfur analyzer (HCS-140, Shanghai Dekai);
[0143] (6) D50 particle size: obtained by laser particle size analyzer;
[0144] (7) Air stability:
[0145] a) The air stability of lithium ferrite supplement was evaluated by comparing the changes in XRD peak intensity at 25°C and 20% relative humidity for different durations.
[0146] b) Assess the air stability of lithium ferrite supplement by comparing the mass change of the supplement in air at 25°C and 20% relative humidity for different durations: the test was conducted at 0.05°C.
[0147] c) The air stability of lithium ferrite supplement was evaluated by comparing its capacity retention rate in air at 25°C and different relative humidities for different durations: the test was conducted at 0.05°C.
[0148] (8) Electrochemical reaction kinetics: The ion diffusion coefficient D was measured by constant current intermittent titration (GITT) and calculated under the conditions of 3.65V-3.75V and 4.00-4.10V.
[0149] Where r is the particle size of the lithium iron ferrite lithium replenisher, τ is the pulse time, ΔEs is the total voltage change caused by the pulse, and ΔEt is the total transient voltage change of the battery within time τ.
[0150] (9) Rate performance: The capacity was tested at 0.05C, 0.1C, 0.2C, 0.5C and 1C respectively.
[0151] 2. Properties test of the positive electrode sheet
[0152] Capacity was tested at 0.1C, 0.2C, 0.3C, 0.5C, 1C, and 2C, and cycling performance was tested at 0.33C.
[0153] 3. Properties test of secondary batteries
[0154] The capacity of the secondary battery was tested under 0.1C, 0.2C, 0.3C, 0.5C, 1C, and 2C conditions, as well as its cycle performance under 0.5C conditions.
[0155] III. Analysis of Test Results for Each Embodiment and Comparative Example
[0156] Tables 1-3 show the performance test results of lithium ferrite supplements.
[0157] Table 1
[0158] Table 2
[0159] The test results above show that the air stability of the lithium ferrite supplements in Examples 1-7 is better than that in Comparative Examples 1-4. Furthermore, the lithium ferrite supplements in this application also exhibit good stability under high humidity conditions, meaning that the shell layer of the lithium ferrite supplement effectively prevents H2O from contacting the LFO in the core layer. In addition, comparing the performance test results of Examples 1-3 and Examples 4-5 reveals that when the mass fraction of carbon in the lithium ferrite supplement is 2%-5%, its air stability is relatively better. This may be because within this range, the shell layer has a better coating effect on the core layer, which is more conducive to preventing the LFO in the core layer from contacting H2O and CO2 in the air. Comparing the performance test results of Examples 1-3 and Examples 6-7 reveals that when the free radical concentration in the lithium ferrite supplement is 1.2 × 10⁻⁶... 13 spins / g ~ 1.8 × 10⁻⁶ 13 At spins / g, its air stability is better.
[0160] Table 3
[0161] Furthermore, as can be seen from the data in Table 3, the specific capacity of the lithium ferrite supplement in the embodiments of this application is higher than 570 mAh / g after 24 hours of storage, and the capacity retention rate is higher than 88%; the specific capacity is higher than 530 mAh / g after 48 hours of storage, and the capacity retention rate is higher than 82%; and the specific capacity is higher than 520 mAh / g after 72 hours of storage, and the capacity retention rate is higher than 80%.
[0162] Furthermore, Figure 1 is a TEM image of the lithium ferrite supplement in Example 1. As can be seen from the figure, the lithium ferrite supplement of this application has a core-shell structure with a uniform shell structure, which forms a good coating on the core material.
[0163] Furthermore, Figure 2 shows the Raman spectra of the lithium ferrite supplement in Example 1 and Comparative Example 1. As can be seen from the figure, the Raman spectrum of Example 1 is at 1350 cm⁻¹. -1 Nearby and 1580cm -1 The presence of D and G peaks nearby indicates that a shell containing carbon material has formed in the lithium ferrite supplement of this application.
[0164] Furthermore, Figure 3 is a SEM image of the lithium ferrite supplement in Example 1 and Comparative Example 1. As can be seen from the figure, the surface of the lithium ferrite supplement with the core-shell structure of this application is smoother, while the surface of the lithium ferrite supplement without carbon coating is rougher. This figure shows that there is a dense shell layer on the surface of the lithium ferrite supplement of this invention, which helps to improve the air stability of LFO.
[0165] Furthermore, Figure 4 shows the XRD patterns of the lithium ferrite supplements in Example 1 and Comparative Example 1 after being placed in air at 25°C and 20% relative humidity for different times. As can be seen from the figure, after 12 hours of placement, the XRD peak intensity of the lithium ferrite supplement in Example 1 did not change significantly, indicating that it has good stability in air. The XRD pattern of the lithium ferrite supplement in Comparative Example 1 after 12 hours of placement in air showed no obvious peak shape, indicating that it has poor air stability.
[0166] Furthermore, Figure 5 shows the GITT test results of the lithium ferrite supplements in Example 1 and Comparative Example 1. As can be seen from the figure, LFO@C in Example 1 has a lower lithium-ion extraction potential compared to LFO in Comparative Example 1, and can release more lithium ions. Calculations show that, within the voltage range of 3.65V-3.75V, the diffusion coefficient D of the lithium ferrite supplement in Example 1 is 5.48 × 10⁻⁶. -11 cm 2 / s, the diffusion coefficient D of the lithium ferrite supplement in Comparative Example 1 is 4.96 × 10⁻⁶. -13 cm 2 / s, Example 1 is approximately 110 times that of Comparative Example 1. Within a voltage range of 4.00V-4.10V, the diffusion coefficient D of the lithium ferrite supplement in Example 1 is 7.88 × 10⁻⁶. -12 cm 2 / s, the diffusion coefficient D of the lithium ferrite supplement in Comparative Example 1 is 1.87 × 10⁻⁶. -12 cm 2 / s, Example 1 is approximately 4 times that of Comparative Example 1. This result is related to the formation of a large number of oxygen vacancy defects during the carbon coating process, which can effectively improve the migration path of lithium ions in LFO.
[0167] Furthermore, Figure 6 shows the specific capacity data of the lithium ferrite supplements in Example 1 and Comparative Example 1 after being placed in air at 25°C and 20% relative humidity for different times. After 8 hours of placement, the specific capacity of the lithium ferrite supplement in Example 1 was 796 mAh / g, with a capacity retention rate of 99.1%. After 24 hours of placement, the specific capacity was 790.1 mAh / g, with a capacity retention rate of 98.4%. After 48 hours of placement, the specific capacity was 764 mAh / g, with a capacity retention rate of 95.2%. After 72 hours of placement, the specific capacity was 745 mAh / g, with a capacity retention rate of 92.8%. In contrast, the capacity retention rate of the lithium ferrite supplement in Comparative Example 1 dropped to 0. This result also indicates that the lithium ferrite supplement in the examples of this application has excellent air stability.
[0168] Furthermore, Figure 7 shows the specific capacity data of the lithium ferrite supplement in Example 1 after being placed at 25°C under different humidity conditions for different times. As can be seen from the figure, after being placed in air with 35% relative humidity for 24 hours, the specific capacity of the lithium ferrite supplement in Example 1 is 779 mAh / g, with a capacity retention rate of 97.1%. In addition, after being placed under 50% relative humidity for 8 hours, the specific capacity of the lithium ferrite supplement still remains above 754 mAh / g, with a capacity retention rate of 94%. This result also shows that the shell layer in the lithium ferrite supplement described in this application can effectively prevent H2O in the air from reacting with LFO in the core layer, thereby improving its air stability.
[0169] Furthermore, Figure 8 shows the rate performance test results of the lithium ferrite supplements in Example 1 and Comparative Example 1. As can be seen from the figure, when the current density increases from 0.05C to 1C, the capacity retention rate of the lithium ferrite supplement in Example 1 is 88%. In contrast, the lithium ferrite supplement in Comparative Example 1 experienced significant capacity decay under the same conditions, with a capacity retention rate of nearly 43%. This result indicates that the electrochemical performance of the lithium ferrite supplement in this application is also significantly improved after carbon coating.
[0170] Furthermore, Figure 9 shows the rate performance and cycle performance of the positive electrode in half-cell in Example 8 and Comparative Example 5. As can be seen from the figure, the specific capacity of the positive electrode material in Example 8 did not drop sharply at rates of 0.1C, 0.2C, 0.3C, 0.5C, 1C, and 2C. The capacity retention rate after 100 cycles at 0.33C was higher than 93%. This result indicates that by adding lithium ferrite as a lithium supplement, the rate performance and cycle performance of the positive electrode were improved to a certain extent.
[0171] Furthermore, Figure 10 is a rate performance test diagram of the secondary battery in Example 9 and Comparative Example 6. As can be seen from the figure, the secondary battery described in this application has good rate performance, and its specific capacity is significantly increased compared with the secondary battery without lithium iron phosphate additive.
[0172] Furthermore, Figure 11 shows the cycle performance test results of the secondary batteries in Example 9 and Comparative Example 6 at 0.5C. As can be seen from the figure, the cycle performance of Example 9 is better than that of Comparative Example 6, and its specific capacity is higher. This result shows that the present application significantly improves the energy density and cycle performance of the secondary battery by adding lithium iron ferrite lithium supplement.
[0173] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.
Claims
1. A lithium ferrite lithium supplement agent, characterized in that, The lithium ferrite lithium supplement agent comprises a core layer and a shell layer coating the surface of the core layer. The core layer is made of Li5FeO4, and the shell layer is made of carbon material. The lithium ferrite lithium supplement agent has I D / I G The value is 1.0 to 1.2, and the average thickness of the shell is 60 nm to 200 nm.
2. The lithium ferrite lithium supplement agent according to claim 1, characterized in that, The free radical concentration of the lithium ferrite supplement is 1.2 × 10⁻⁶. 13 spins / g ~ 1.8 × 10⁻⁶ 13 spins / g.
3. The lithium ferrite lithium supplement agent according to claim 1, characterized in that, The lithium ferrite supplement contains 2% to 5% carbon by mass.
4. The lithium ferrite supplement agent according to any one of claims 1 to 3, characterized in that, The D50 particle size of the lithium ferrite supplement is 3μm to 6μm.
5. The lithium ferrite supplement agent according to any one of claims 1 to 3, characterized in that, Includes at least one of the following features: (1) The specific capacity of the lithium ferrite supplement after being exposed to air at 25°C and 20% relative humidity for 24 hours is higher than 570mAh / g; (2) The specific capacity of the lithium ferrite supplement after being exposed to air at 25°C and 20% relative humidity for 48 hours is higher than 530mAh / g; (3) The specific capacity of the lithium ferrite supplement after being exposed to air at 25°C and 20% relative humidity for 72 hours is higher than 520mAh / g.
6. The lithium ferrite supplement agent according to any one of claims 1 to 3, characterized in that, Includes at least one of the following features: (1) The capacity retention rate of the lithium ferrite supplement after being exposed to air at 25°C and 20% relative humidity for 24 hours is above 88%; (2) The capacity retention rate of the lithium ferrite supplement after being exposed to air at 25°C and 20% relative humidity for 48 hours is above 82%; (3) The capacity retention rate of the lithium ferrite supplement after being exposed to air at 25°C and 20% relative humidity for 72 hours is above 80%.
7. A positive electrode material, characterized in that, The positive electrode material includes a positive electrode active material, a conductive agent, a binder, and a lithium replenishing agent, wherein the lithium replenishing agent is the lithium ferrite lithium replenishing agent according to any one of claims 1 to 6; the mass ratio of the lithium replenishing agent to the positive electrode active material is (1:100) to (5:100).
8. The cathode material according to claim 7, characterized in that, The cathode material retains more than 93% of its capacity after 100 cycles at a 0.33C rate.
9. A positive electrode sheet, characterized in that, It includes a current collector and a positive electrode material located on one or both sides of the current collector; wherein the positive electrode material is the positive electrode material of claim 8.
10. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, and a separator, wherein the positive electrode is the positive electrode as described in claim 9.