A phosphate spherical material and its preparation method, a composite cathode material and its preparation method, and a lithium-ion battery.

Abstract

This invention discloses a phosphate spherical material and its preparation method, wherein the intensity ratio of the (020) crystal plane peak to the (311) crystal plane peak in the X-ray diffraction pattern is 0.95≥I(020) / I(311)≥0.88; this invention also discloses a composite cathode material and its preparation method, wherein the composite cathode material includes a mixed composite phosphate spherical material and a ternary material; wherein the intensity ratio of the (020) crystal plane peak to the (311) crystal plane peak in the X-ray diffraction pattern of the phosphate spherical material is 0.95≥I(020) / I(311)≥0.88; this invention also discloses a lithium-ion battery that can optimize energy density while ensuring thermal safety.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a phosphate spherical material and its preparation method, a composite cathode material and its preparation method, and a lithium-ion battery. Background Technology

[0002] In the current field of lithium-ion power batteries, the performance of cathode materials directly determines the energy density, safety performance and cycle life of the battery. However, due to their inherent characteristics, mainstream cathode materials generally have a core technical contradiction of "it is difficult to achieve both high energy density and high safety". Specifically, this is reflected as follows: On the one hand, ternary materials with layered structures (such as NCM and NCA), with their high specific capacity (usually >200mAh / g) and high operating voltage platform, can enable lithium-ion power batteries to achieve an energy density of 200-300Wh / kg, which can effectively meet the needs of electric vehicles for long driving range, especially in high-end models and low-temperature application scenarios. However, the poor thermal stability of layered ternary materials is a fatal weakness: as the nickel content increases, the stability of the material's crystal structure decreases sharply at high temperatures, resulting in a low thermal runaway trigger temperature (130-200℃, which decreases significantly with increasing state of charge); moreover, the thermal runaway process is accompanied by violent oxygen release, which can easily react with the battery electrolyte in a chain exothermic reaction, leading to serious safety accidents such as fires and explosions, greatly limiting its application in high-safety-requirement scenarios. On the other hand, phosphate materials with an olivine structure (such as LFP and LMFP), relying on a robust PO covalent bond framework, possess excellent thermal and chemical stability, and their thermal runaway temperature is usually higher than 270℃, effectively avoiding the risk of thermal runaway; at the same time, they have the advantages of long cycle life (usually >3000 cycles) and low cost, and are widely used in low-to-mid-range electric vehicles, energy storage, and other fields. However, phosphate materials with olivine structure have significant shortcomings in energy density and dynamic performance: their theoretical specific capacity is low (about 170 mAh / g), and their operating voltage platform is not high (about 3.2V for LFP and about 4.1V for LMFP), resulting in a battery energy density of only 140-180Wh / kg; in addition, their rate performance is relatively low, which restricts the breakthrough of fast charging performance and makes it difficult to meet the dual demands of the high-end market for "extreme battery life + fast charging".

[0003] The performance defects of the two materials mentioned above create a "seesaw" effect: a single material system cannot simultaneously meet the market's composite performance requirements for lithium-ion power batteries, namely "high safety, long range, long life, and wide temperature range," becoming a key bottleneck restricting the upgrading of next-generation power battery technology.

[0004] To reconcile the aforementioned contradictions, the industry has explored a technical route of "mixing ternary materials with phosphate materials (LFP / LMFP)," attempting to achieve complementary advantages between the two materials through physical mixing or simple composites. However, existing hybrid technologies all have significant limitations and fail to fundamentally solve the core bottleneck problem. Specific defects are as follows: 1. Thermal runaway diffusion in composite materials remains difficult to effectively suppress: Ternary materials (especially high-nickel ternary materials) have a low thermal runaway trigger temperature, releasing a large amount of combustible material and heat during thermal runaway. Existing composite technologies are mostly simple physical mixing. At the electrode microscale, the heat released by ternary particles can be quickly conducted to adjacent areas through interparticle contact points or conductive networks. Although the thermal conductivity of phosphate materials (1~2W / mK) is not significantly lower than that of ternary materials (2~4W / mK), it is still insufficient to effectively block the spread of heat in a timely manner, failing to effectively improve safety performance at the battery level, and the risk of thermal runaway diffusion remains prominent. 2. Mismatch in electrochemical performance between composite components: There are significant differences between ternary materials and phosphate materials in rate performance and low-temperature performance. In terms of rate performance, the ion diffusion coefficient of phosphate materials (10) -14 ~10 -13 cm 2 The efficiency ( / s) of composite electrodes is 2-3 orders of magnitude higher than that of ternary materials. During high-rate charge and discharge of composite electrodes, the phosphate component is prone to severe polarization, becoming a bottleneck region for Li ion insertion and extraction. This not only reduces the overall rate performance of the battery but also forces the ternary component to bear excess current, accelerating the structural degradation of the ternary material. In terms of low-temperature performance, the Li ion diffusion barrier of phosphate materials increases sharply at low temperatures, resulting in significant capacity decay (e.g., at -20℃, the LFP capacity can decay to less than 50% of the room temperature capacity), leading to near "deactivation" at low temperatures. This phenomenon causes a sharp drop in the overall output power of the battery pack, and local areas are prone to lithium plating due to overload, further exacerbating safety risks.

[0005] Therefore, the industry currently lacks an effective technical solution that can deeply synergize the high energy density of ternary materials with the high safety of phosphate materials. The market urgently needs an innovative material or structural design that can achieve complementary advantages and seamless synergy between the two materials at the nano / micro scale, rather than simply physical stacking or layering, thereby truly optimizing energy density while ensuring thermal safety and meeting the stringent requirements of next-generation power batteries.

[0006] In view of this, the inventors developed this invention. Summary of the Invention

[0007] The purpose of this invention is to provide a phosphate spherical material and its preparation method, a composite cathode material and its preparation method, and a lithium-ion battery, which can optimize energy density while ensuring thermal safety.

[0008] To achieve the above objectives, the present invention adopts the following solution:

[0009] A phosphate spherical material, the intensity ratio of the (020) crystal plane peak to the (311) crystal plane peak in the X-ray diffraction pattern is 0.95≥I(020) / I(311)≥0.88.

[0010] A method for preparing the above-mentioned phosphate spherical material includes:

[0011] S1, lithium source, M element source, phosphorus source and solvent are mixed, hydrothermally synthesized and purified to obtain pure phase phosphate single particles;

[0012] S2. After mixing the obtained pure phase phosphate single particles with a carbon source aqueous solution, spray granulation and high-temperature sintering are performed to obtain phosphate spherical material.

[0013] In an exemplary embodiment, in step S1, the lithium source is selected from one or more of lithium carbonate, lithium sulfate, lithium hydroxide, and lithium phosphate; the M element source is selected from one or more of sulfates, nitrates, and oxalates of the corresponding element; the phosphorus source is phosphoric acid; and the solvent is one or more of water, ethylene glycol, ethanol, and diethylene glycol.

[0014] In an exemplary embodiment, the amounts of the lithium source, the M element source, and the phosphorus source are in a molar ratio of (2.70~3.10): 1: (0.97~1.02).

[0015] In an exemplary embodiment, the hydrothermal synthesis temperature is 150~210°C, and the hydrothermal synthesis time is 1~3 hours.

[0016] In an exemplary embodiment, in step S2, the carbon source is one or more of sucrose, glucose, polyethylene glycol, oxalic acid, citric acid, hexadecyltrimethylammonium bromide, thioacetamide, and phenolic resin, and the amount of carbon source added is 2.0~15.0 wt., based on the mass of a single pure phase phosphate particle.

[0017] In an exemplary embodiment, in step S2, the spray granulation uses a multi-fluid spraying device with a spray pressure of 0.4~0.8MPa, a spray drying chamber temperature of 140~180℃, a sintering temperature of 650~730℃, and a sintering time of 1~10h.

[0018] A composite cathode material includes a mixed composite phosphate spherical material and a ternary material; the intensity ratio of the (020) crystal plane peak to the (311) crystal plane peak in the X-ray diffraction pattern of the phosphate spherical material is 0.95≥I(020) / I(311)≥0.88.

[0019] In an exemplary embodiment, the phosphate spherical material is lithium iron phosphate spherical material, and the average diameter of the primary particles of the lithium iron phosphate spherical material is in the range of [40, 150] nm.

[0020] In an exemplary embodiment, the phosphate spherical material is lithium manganese iron phosphate spherical material, and the average diameter of the primary particles of the lithium manganese iron phosphate spherical material is in the range of [30, 100] nm.

[0021] In an exemplary embodiment, the phosphate spherical material is formed by the agglomeration of nanoscale primary particles, and the closed-pore porosity of the phosphate spherical material is [0,5] vol.%.

[0022] In an exemplary embodiment, the phosphate spherical material and the ternary material are mixed and compounded by stirring.

[0023] A method for preparing the above-mentioned composite cathode material includes: mixing and compounding phosphate spherical materials with ternary materials.

[0024] A lithium-ion battery comprising the above-mentioned composite cathode material or the composite cathode material prepared by the above-mentioned method for preparing the composite cathode material.

[0025] As can be seen from the above technical solution, when using the composite cathode material prepared by the phosphate spherical material of the present invention to prepare a battery, the intensity ratio of the (020) crystal plane peak to the (311) crystal plane peak in the X-ray diffraction pattern of the phosphate spherical material is 0.95 ≥ I(020) / I(311) ≥ 0.88, which can ensure thermal safety and make the (020) crystal plane (Li + The full exposure of the insertion / extraction main channel (020) optimizes energy density by significantly exposing the Li crystal plane. + The reduced migration resistance allows for more complete insertion and extraction, thus increasing energy density; combined with the high stacking efficiency of the spherical morphology, the energy density advantage is further amplified. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0027] Figure 1 The XRD patterns of lithium manganese iron phosphate materials in Example 1 and Comparative Example 2 of this invention are shown. Detailed Implementation

[0028] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided so that this disclosure will be more comprehensive and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0029] This invention discloses a phosphate spherical material, in which the intensity ratio of the (020) crystal plane peak to the (311) crystal plane peak in the X-ray diffraction pattern is 0.95≥I(020) / I(311)≥0.88.

[0030] This invention also discloses a method for preparing the above-mentioned phosphate spherical material, comprising:

[0031] S1, lithium source, M element source, phosphorus source and solvent are mixed, hydrothermally synthesized and purified to obtain pure phase phosphate single particles;

[0032] S2. After mixing the obtained pure phase phosphate single particles with a carbon source aqueous solution, spray granulation and high-temperature sintering are performed to obtain phosphate spherical material.

[0033] In an exemplary embodiment, in step S1, the lithium source is selected from one or more of lithium carbonate, lithium sulfate, lithium hydroxide, and lithium phosphate; the M element source is selected from one or more of sulfates, nitrates, and oxalates of the corresponding element; the phosphorus source is phosphoric acid; the solvent is one or more of water, ethylene glycol, ethanol, and diethylene glycol; and the "M element source" is a raw material that provides the metal element in the phosphate.

[0034] The amounts of lithium source, M element source and phosphorus source are in the following molar ratio: (2.70~3.10):1:(0.97~1.02).

[0035] In an exemplary embodiment, the hydrothermal synthesis temperature is 170~190°C, and the hydrothermal synthesis time is 1~3 hours.

[0036] In an exemplary embodiment, in step S2, the carbon source is one or more of sucrose, glucose, polyethylene glycol, oxalic acid, citric acid, hexadecyltrimethylammonium bromide, thioacetamide, and phenolic resin. Based on the mass of a single pure-phase phosphate particle, the amount of carbon source added is 2.0~15.0 wt.%. The equipment used for spray granulation is a multi-fluid spraying device, with a nozzle spray pressure of 0.4~0.8 MPa and a spray drying chamber temperature of 140~180℃. The sintering temperature is 650~730℃, and the sintering time is 1~10 h.

[0037] The present invention also discloses a composite cathode material, comprising a mixed composite phosphate spherical material and a ternary material; the intensity ratio of the (020) crystal plane peak to the (311) crystal plane peak in the X-ray diffraction pattern of the phosphate spherical material is 0.95≥I(020) / I(311)≥0.88.

[0038] In an exemplary embodiment, the phosphate spherical material is lithium iron phosphate spherical material, and the average diameter of the primary particles of the lithium iron phosphate spherical material is in the range of [40, 150] nm.

[0039] In an exemplary embodiment, the phosphate spherical material is lithium manganese iron phosphate spherical material, and the average diameter of the primary particles of the lithium manganese iron phosphate spherical material is in the range of [30, 100] nm.

[0040] In an exemplary embodiment, the phosphate spherical material is formed by the agglomeration of nanoscale primary particles, and the closed-pore porosity of the phosphate spherical material is [0,5] vol.%.

[0041] In an exemplary embodiment, the phosphate spherical material and the ternary material are mixed and compounded by stirring.

[0042] The ternary material can be a low- or medium-nickel ternary material or a high-nickel ternary material, and can be either single-crystal or polycrystalline, with high-nickel ternary material being preferred.

[0043] The present invention also discloses a method for preparing the above-mentioned composite cathode material, comprising: mixing and compounding phosphate spherical material with ternary material.

[0044] The present invention also discloses a lithium-ion battery comprising the above-mentioned composite cathode material or the composite cathode material prepared by the above-mentioned method for preparing composite cathode material.

[0045] Therefore, when using the composite cathode material prepared from the phosphate spherical material of this invention to prepare a battery, the intensity ratio of the (020) crystal plane peak to the (311) crystal plane peak in the X-ray diffraction pattern of the phosphate spherical material is 0.95 ≥ I(020) / I(311) ≥ 0.88, which can ensure thermal safety and make the (020) crystal plane (Li + The full exposure of the insertion / extraction main channel (020) optimizes energy density by significantly exposing the Li crystal plane. + The reduced migration resistance and more complete insertion / extraction result in increased energy density; combined with the high stacking efficiency of the spherical morphology, the energy density advantage is further amplified.

[0046] Furthermore, the present invention prepares the phosphate spherical material through hydrothermal synthesis, and by combining the design of the primary particle average diameter (hereinafter referred to as primary particle size) and closed-pore porosity of the phosphate spherical material, thermal safety can be further optimized, as detailed below:

[0047] (1) The spherical phosphate material prepared by hydrothermal synthesis has higher rate performance than traditional phosphate materials due to its nanoscale primary particle size. The hydrothermal synthesis method prepares phosphate materials with a higher (020) crystal plane exposure ratio, which further improves the rate performance. When used in combination with ternary materials, under high battery conditions, the current is relatively uniformly dispersed among the components in the composite material, avoiding polarization deterioration and attenuation of the positive electrode, thereby improving the performance mismatch when phosphate and ternary materials are used in combination.

[0048] (2) In addition, although nanoscale phosphate materials have higher electrochemical activity due to their higher exposed surface area, their relatively poor conductivity will lead to an increased risk of overcharge lithium plating and irreversible structural distortion (Li ion insertion and extraction are hindered during overcharge, which easily leads to lattice distortion). Ternary materials have good rate performance throughout the entire SOC range, and the Li ion diffusion coefficient is significantly higher than that of phosphate materials, allowing the entire battery pack to accept a larger charging current at a higher average SOC without easily causing non-uniform ion extraction in LFP, thereby improving the overcharge tolerance of phosphate materials - uniform ion flow.

[0049] (3) The spherical material contains a certain number of pores, mainly filled with nitrogen. Its thermal conductivity of 0.024 W / mK is two orders of magnitude lower than that of phosphate materials or ternary materials, making it an excellent thermal resistance material. It will suppress heat transfer within the microscale of the electrode and delay the occurrence of thermal runaway in ternary materials. In addition, it will block the oxygen released by ternary materials to a certain extent, suppressing the chain combustion that occurs during thermal runaway, thereby suppressing the diffusion of thermal runaway in ternary materials—porous thermal resistance.

[0050] Examples and Comparative Examples

[0051] To protect the "hydrothermal synthesis small particle size 150 / 100nm", "crystal plane peak intensity ratio", and "closed-pore porosity", the following implementation / comparative example was made: spherical lithium manganese iron phosphate (Mn / Fe=70 / 30) + high-nickel polycrystalline ternary material (D50 of 10.0 and 10.0μm respectively), with a mass ratio of 80%:20%.

[0052] In Example 1, in step S1 of preparing spherical lithium manganese iron phosphate, lithium carbonate, ferrous sulfate, manganese sulfate, and phosphoric acid are selected as the main raw materials, mixed or dissolved in an aqueous solvent, wherein the molar ratio of ferrous sulfate to manganese sulfate is 3:7. After the resulting homogeneous mixture is hydrothermally synthesized at 170~190℃ for 1 hour, the slurry is subjected to solid-liquid separation and washing (purification treatment) to obtain lithium manganese iron phosphate material. In step S2, a mixed aqueous solution of glucose, polyethylene glycol, and citric acid is added to the obtained lithium manganese iron phosphate material, with the total mass of the three carbon sources being 12wt.%. Granulation is performed by multifluid spraying, wherein the spray pressure is 0.4~0.8MPa, the spray drying chamber temperature is 140~180℃, and then sintering is carried out at 660~700℃ for 1~3 hours to obtain spherical lithium manganese iron phosphate.

[0053] Subsequently, a composite cathode material was prepared: spherical lithium manganese iron phosphate (Mn / Fe=70 / 30) + high-nickel polycrystalline ternary material (D50 of 10.0 and 10.0 μm respectively), with a mass ratio of 80%:20%; the composite cathode material was obtained by stirring and mixing at 100~200 rpm for 1~4 hours in a planetary mixer.

[0054] The difference between Example 2 and Example 1 lies only in the following: During spray granulation, the temperature of the spray drying chamber is increased to 180°C, which promotes rapid drying of the outer layer of the spherical material to form a hard surface layer, reducing particle shrinkage during the drying process and thus increasing porosity. Simultaneously, the sintering time is extended to 3 hours, allowing the crystal structure of the phosphate material to recrystallize further during sintering. The material exhibits a decrease in XRD peak intensity ratio and an increase in closed-cell porosity in the phosphate spherical material.

[0055] The only difference between Example 3 and Example 1 is that the hydrothermal synthesis temperature is reduced to 170°C, resulting in a lower degree of hydrothermal crystallization and a relatively smaller exposed area of ​​the (020) crystal face. During spray granulation, the spray drying temperature is reduced to 140°C to prolong the drying time and promote the full drying and shrinkage of the spherical material. The XRD peak intensity ratio of the phosphate spherical material is reduced, as is the closed-cell porosity.

[0056] The only difference between Comparative Example 1 and Example 1 is that the hydrothermal synthesis temperature was reduced to 160°C, resulting in a lower degree of hydrothermal crystallization and a relatively smaller exposed area of ​​the (020) crystal face. The XRD peak intensity of the phosphate spherical material was also reduced.

[0057] The only difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses conventional high-temperature solid-state sintering to obtain phosphate single particles. It only achieves good induction of (020) crystal plane exposure under hydrothermal conditions and possesses the capability for nano-fabrication. Therefore, the resulting spherical phosphate particles have relatively low XRD peak intensity and larger primary particles.

[0058] The only difference between Comparative Example 3 and Example 1 is that the hydrothermal synthesis temperature is reduced to 170°C, resulting in a lower degree of hydrothermal crystallization and a relatively smaller exposed area of ​​the (020) crystal face. During spray granulation, the temperature of the spray drying chamber is increased to 210°C to promote rapid drying of the outer layer of the spherical material, forming a hard surface layer, reducing particle shrinkage during the drying process, and thus increasing porosity. XRD peak intensity ratio and closed-cell porosity of phosphate spherical material.

[0059] The different material properties and performance test results of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1 below.

[0060] Table 1

[0061]

[0062] In Example 1, spherical lithium manganese iron phosphate material with an XRD intensity ratio of 0.92 between the (020) crystal plane peak and the (311) crystal plane peak in the X-ray diffraction pattern was used and compounded with the above-mentioned high-nickel polycrystalline ternary material. The ratio of 5C discharge capacity to 0.1C discharge capacity (power performance) was 87.8%. After the coin cell was fully charged, it was disassembled and the positive electrode powder was scraped off for DSC testing, which showed that its exothermic peak temperature was 207.6℃ and the highest exothermic rate was 1.798mW.

[0063] In Example 2, spherical lithium manganese iron phosphate material with an XRD intensity ratio of 0.90 between the (020) and (311) crystal plane peaks in the X-ray diffraction pattern was used in combination with the above-mentioned high-nickel polycrystalline ternary material. The ratio of 5C discharge capacity to 0.1C discharge capacity (power performance) was 85.7%, which was lower than that in Example 1, mainly because the exposure of the (020) active crystal plane was reduced. After the coin cell was fully charged, it was disassembled and the positive electrode powder was scraped off for DSC testing. The results showed that its exothermic peak temperature was 209.0℃ and the highest exothermic rate was 1.694mW. This was attributed to the increased porosity of the material, which increased the thermal resistance during thermal runaway and prevented rapid heat conduction.

[0064] In Example 3, spherical lithium manganese iron phosphate material with an XRD intensity ratio of 0.88 between the (020) and (311) crystal plane peaks was used in combination with the above-mentioned high-nickel polycrystalline ternary material. The ratio of 5C discharge capacity to 0.1C discharge capacity (power performance) was 85.0%, which was close to that in Example 2. This is attributed to the power performance reduction caused by the decrease in XRD peak intensity ratio, which to some extent offsets the power performance improvement caused by the accelerated charge transfer due to the reduction in closed-pore porosity. After the coin cell was fully charged, it was disassembled and the positive electrode powder was scraped off for DSC testing. The results showed that its exothermic peak temperature was 206.8℃ and the highest exothermic rate was 1.817mW, proving that the reduction in porosity is not conducive to the improvement of thermal stability.

[0065] In Comparative Example 1, the spherical lithium manganese iron phosphate material with an XRD peak intensity ratio I(020) / I(311) reduced to 0.87 was compounded with the above-mentioned high-nickel polycrystalline ternary material. The active surface area of ​​the phosphate material was reduced, resulting in a decrease in the power performance of the compounded material to 82.1%, but the effect on thermal stability was not significant.

[0066] In Comparative Example 2, lithium manganese iron phosphate material prepared by solid-state method was used. The XRD peak intensity ratio I(020) / I(311) of the spherical lithium manganese iron phosphate material was reduced to 0.82. When combined with the above-mentioned high-nickel polycrystalline ternary material, its particle size was larger than that of the hydrothermal method material. The XRD spectrum showed that the relative intensity of the (020) crystal plane diffraction peak at 29° relative to the (311) peak at 35° was lower than that in Example 1. Figure 1 As shown, the power performance of the resulting material further decreases, but the effect on thermal stability is still not significant.

[0067] In Comparative Example 3, a lithium manganese iron phosphate cathode material with a higher closed-cell porosity (6%) and a spherical lithium manganese iron phosphate material with an XRD peak intensity ratio I(020) / I(311) of 0.88 were used in combination with the above-mentioned high-nickel polycrystalline ternary material. Due to the deterioration of the conductive network between the primary particles of lithium manganese iron phosphate, the power performance of the material deteriorated to 82.7%. However, due to the increased number of closed pores inside, the thermal resistance effect was higher, and the temperature at which the composite material experienced thermal runaway increased to 211.8℃. The peak power of the exothermic reaction decreased, indicating that the exothermic reaction was slower.

[0068] Compared with Comparative Example 1, Example 1 differs only in the XRD peak intensity ratio of the phosphate spherical material; all other conditions are the same. The XRD peak intensity ratio of the phosphate spherical material in Comparative Example 1 is lower than 0.88. This indicates that the XRD peak intensity ratio of the phosphate spherical material is lower than 0.88, resulting in a lower 5C discharge capacity / 0.1C discharge capacity, a lower DSC exothermic peak temperature, and a higher DSC exothermic peak height (thermal runaway exothermic rate). Consequently, the synergistic optimization effect of energy density and thermal safety is worse. The composite cathode material prepared in this application has higher rate performance and higher energy density.

[0069] Compared with Comparative Example 3, Example 3 differs only in the closed-cell porosity; all other conditions are the same. Comparative Example 3 has a closed-cell porosity greater than 5 vol.%, a low 5C discharge capacity / 0.1C discharge capacity, and a high DSC exothermic peak temperature, indicating a higher upper limit of the material's safe temperature. Furthermore, the low DSC exothermic peak height (thermal runaway exothermic rate) indicates that the material releases heat slowly during thermal runaway. However, the higher porosity in Comparative Example 3 hinders rapid charge transfer, resulting in a lower 5C discharge capacity. Therefore, although the material in Comparative Example 3 exhibits good thermal stability, its low 5C discharge capacity leads to a poorer synergistic optimization effect on energy density and thermal safety.

[0070] Therefore, as can be seen from the above comparison, the technical solution of this application can significantly improve energy density while ensuring thermal safety. Even if the DSC exothermic peak temperature and DSC exothermic peak height (thermal runaway exothermic rate) are within a suitable range, the 5C discharge capacity / 0.1C discharge capacity can reach more than 85%, thus improving the synergistic optimization effect of energy density and thermal safety.

[0071] It should be understood that the various examples described above can be utilized in multiple directions, such as tilted, inverted, horizontal, vertical, etc., and in multiple configurations, without departing from the principles of the invention. The embodiments shown in the accompanying drawings are merely examples of effective application of the principles of the invention, and the invention is not limited to any specific details of these embodiments.

[0072] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the appended claims.

Claims

1. A method for preparing spherical phosphate material, characterized in that, include: S1, lithium source, M element source, phosphorus source and solvent are mixed, hydrothermally synthesized and purified to obtain pure phase phosphate single particles; S2. After mixing the obtained pure phase phosphate single particles with the carbon source aqueous solution, spray granulation and high-temperature sintering are carried out to obtain phosphate spherical material. The sintering temperature is 650~730℃ and the spray drying chamber temperature is 140~180℃. In step S1, the lithium source is selected from one or more of lithium carbonate, lithium sulfate, lithium hydroxide, and lithium phosphate; the M element source is selected from ferrous sulfate and manganese sulfate; the phosphorus source is phosphoric acid; and the solvent is one or more of water, ethylene glycol, ethanol, and diethylene glycol. The amounts of lithium source, M element source, and phosphorus source used are in a molar ratio of (2.70~3.10):1:(0.97~1.02); The hydrothermal synthesis temperature is 170~190℃, and the hydrothermal synthesis time is 1~3h; The intensity ratio of the (020) crystal plane peak to the (311) crystal plane peak in the X-ray diffraction pattern of the phosphate spherical material is 0.95 ≥ I(020) / I(311) > 0.

88.

2. The method for preparing phosphate spherical materials according to claim 1, characterized in that, In step S2, the carbon source is one or more of sucrose, glucose, polyethylene glycol, oxalic acid, citric acid, hexadecyltrimethylammonium bromide, thioacetamide, and phenolic resin. Based on the mass of a single pure phase phosphate particle, the amount of carbon source added is 2.0~15.0 wt.%.

3. The method for preparing phosphate spherical materials according to claim 1 or 2, characterized in that, In step S2, the spray granulation is performed using a multi-fluid spraying device with a spray pressure of 0.4~0.8MPa and a sintering time of 1~10h.

4. A phosphate spherical material, characterized in that: It is prepared by the method for preparing phosphate spherical material as described in any one of claims 1 to 3.

5. A composite cathode material, characterized in that, The mixture includes the phosphate spherical material and ternary material as described in claim 4, which are combined in a composite manner; the intensity ratio of the (020) crystal plane peak to the (311) crystal plane peak in the X-ray diffraction pattern of the phosphate spherical material is 0.95≥I(020) / I(311)>0.88; the phosphate spherical material is lithium manganese iron phosphate spherical material, and the average diameter of the primary particles of the lithium manganese iron phosphate spherical material is in the range of 30~100nm.

6. The composite cathode material according to claim 5, characterized in that, The phosphate spherical material is formed by the agglomeration of nano-sized primary particles, and the closed-pore porosity of the phosphate spherical material is 0~5 vol.%.

7. The composite cathode material according to claim 5 or 6, characterized in that: The phosphate spherical material and the ternary material are mixed and compounded by stirring.

8. A lithium-ion battery, characterized in that, Includes the composite cathode material as described in any one of claims 5 to 7.

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