Lithium manganese iron phosphate composite positive electrode particle with high-strength conductive carbon

Abstract

The invention discloses a lithium manganese iron phosphate composite positive electrode particle with high-strength conductive carbon, the structure of the composite positive electrode particle comprises an LMFP (lithium manganese iron phosphate) particle and a conductive layer coated on the outer surface of the LMFP particle, and the LMFP particle and the conductive layer jointly form the composite positive electrode particle; the conductive layer comprises a plurality of carbon clusters and a plurality of lithium ion conductor particles and is used for improving conductivity; wherein the carbon clusters in the conductive layer are formed by dehydrating carbohydrates, water-soluble fibers or amino acid polymers; the plurality of lithium ion conductor particles are distributed in the conducting layer, close to the outer part of the conducting layer or close to the outer surface of the LMFP particles; the lithium ion conductor particles refer to oxides or phosphates with lithium ion conductivity, or oxides with garnet or perovskite structures. In addition, the conductive layer further comprises a plurality of conductive carbons, and the conductive carbons are selected from at least one of graphite, graphene, nanoscale amorphous carbon or carbon nanotubes with the length not larger than 1 micrometer.

Description

Technical Field

[0001] This invention relates to the field of battery cathode material technology, and in particular to a lithium iron phosphate composite cathode particle with high-strength conductive carbon. Background Technology

[0002] A battery consists of a positive electrode and a negative electrode, with the cathode being the positive electrode inside the battery. This positive electrode mainly comprises a positive electrode substrate and a positive electrode slurry layer coated on it. The positive electrode slurry layer consists of a positive electrode slurry containing a binder and a large number of positive electrode particles.

[0003] Positive electrode particles are mainly used as the positive electrode in general solid-state or solid-state-like batteries. They must possess conductive or conductive properties to allow free electrons to migrate smoothly in the positive electrode slurry, avoiding excessive energy consumption due to high internal resistance, thereby achieving efficient conductivity. Therefore, when manufacturing positive electrode particles, it is necessary to consider using specific conductive materials to adjust their conductivity.

[0004] Traditionally, LMFP (lithium manganese iron phosphate) has been used as the cathode material, an improvement on traditional lithium iron phosphate (LFP). By introducing manganese, LMFP outperforms traditional lithium iron phosphate in terms of operating voltage and can deliver higher energy density. LMFP's advantages lie in its low cost and hydrophobicity, making it a fairly common cathode material.

[0005] However, LMFPs exhibit poor rate charge / discharge performance, and their lithium conductivity and electrical conductivity are not ideal. Furthermore, their structure is prone to aging during long-term battery use, leading to a reduction in battery life. While various methods have been developed to improve the lithium-ion conductivity of cathode particles, the conductivity of lithium batteries in practical applications remains insufficient. Therefore, the inventors aim to propose a novel design that enables the cathode of existing solid-state batteries to possess higher capacity and conductivity, thereby further enhancing the overall performance of the battery. Therefore, existing technologies have shortcomings and need to be improved. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art by proposing a "high-strength conductive carbon-based lithium manganese iron phosphate composite cathode particle". This is achieved by coating the surface of the LMFP particle with a conductive layer, thus comprehensively improving its performance. LMFP is significantly cheaper than ternary oxides. Although its charge-discharge performance is not as good as ternary materials, it is sufficient for specific applications. Therefore, using LMFP as the cathode material can significantly reduce battery production costs.

[0007] Coating the LMFP particles with a conductive layer can compensate for the poor conductivity of LMFPs; at the same time, introducing a large number of lithium-ion conductor particles on the outer surface of LMFPs can further improve the overall lithium-ion conduction capability, thereby simultaneously improving conductivity and lithium-ion conduction performance and achieving better battery performance.

[0008] To achieve the above objectives, this invention proposes a "lithium manganese iron phosphate composite cathode particle with high-strength conductive carbon" for use in the cathode of solid-state or near-solid-state batteries. Its structure includes: One LMFP (lithium manganese iron phosphate) particle; A conductive layer is coated on the outer surface of the LMFP particle, and the two together constitute the composite positive electrode particle.

[0009] The conductive layer contains: 1. Numerous carbon clusters, used to enhance electrical conductivity. These carbon clusters can be formed in any of the following ways: Carbon clusters formed after carbohydrates are dehydrated; Carbon-containing skeletons and carbon clusters with some functional groups formed after water-soluble fibers are dehydrated; Carbon clusters containing doped elements, with straight or branched carbon skeletons, formed after the dehydration of amino acid polymers.

[0010] 2. Numerous lithium-ion conductive particles are distributed inside the conductive layer, near the outside of the conductive layer, or near the outer surface of the LMFP particles to enhance lithium conductivity. These particles are made of oxides or phosphates with lithium-ion conductivity, or oxides with garnet or perovskite structures.

[0011] 3. A variety of conductive carbon materials (selected from at least one of graphite, graphene, nano-amorphous carbon, or carbon nanotubes with a length ≤1μm) are used to connect carbon clusters in the conductive layer, enabling electrons to be transported across carbon clusters and further improving the overall conductivity efficiency.

[0012] The features and advantages of the present invention can be further understood through the following description and in conjunction with the accompanying drawings. Attached Figure Description

[0013] Figure 1 This shows a schematic diagram of the cross-section of the composite positive electrode particles of the present invention.

[0014] Figure 2 Examples of applications of the present invention are shown.

[0015] Figure 3 The diagram shows the composite positive electrode particle structure and an enlarged schematic diagram of the present invention.

[0016] Figure 4 This diagram shows the composite cathode particle structure of the carbon-coated material of the present invention.

[0017] Figure 5 This diagram shows the structure of the lithium-ion composite conductor particles of the present invention.

[0018] Among them, 5 is a borate layer; 10 is lithium-ion conductor particles; 40 is carbon nanotubes; 42 is short-chain carbon nanotubes; 44 is long-chain carbon nanotubes; 45 is nanoscale amorphous carbon; 100 is a positive electrode; 101 is lithium-ion composite conductor particles; 105 is a positive electrode substrate; 103 is a positive electrode slurry; 108 is a positive electrode slurry layer; 121 is LMFP particles; 122 is a conductive layer; 123 is a carbon cluster; 124 is conductive carbon; 200 is a composite positive electrode particle; and 280 is a composite positive electrode particle coated with carbon material. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0020] Please refer to Figures 1 to 5 As shown, this invention relates to a lithium manganese iron phosphate composite cathode particle with high-strength conductive carbon, used in the cathode 100 of a solid-state or near-solid-state battery. The cathode 100 mainly comprises: Positive substrate 105 (e.g.) Figure 2 (as shown) A positive electrode slurry layer 108 is coated on the positive electrode substrate 105. The positive electrode slurry layer 108 includes a positive electrode slurry 103 containing a binder and a plurality of composite positive electrode particles 200.

[0021] The total weight of multiple composite cathode particles 200 accounts for 88 wt% to 98 wt% of the weight of the cathode slurry layer 108.

[0022] like Figure 1 As shown, the structure of each composite cathode particle 200 includes: A single LMFP (lithium manganese iron phosphate) particle 121 has a D50 particle size (median particle size distribution) of less than 1 micrometer and is in the form of a single crystal material or a microcrystalline aggregate.

[0023] The LMFP particles 121 may be lithium manganese iron phosphate (LiMnxFe1-xPO4, x is between 0.1 and 0.8) or lithium manganese iron phosphate doped with at least one metal element.

[0024] A conductive layer 122 is coated on the outer surface of LMFP particles 121, forming a composite positive electrode particle 200.

[0025] The conductive layer 122 includes multiple carbon clusters 123 and multiple lithium-ion conductor particles 10 to improve conductivity.

[0026] The carbon clusters 123 are made from a carbon source added during the preparation of the composite cathode particles 200. The carbon source is an organic compound that can form carbon under a reducing atmosphere, selected from carbohydrates (such as at least one of monosaccharides, disaccharides, oligosaccharides, and polysaccharides), water-soluble fibers, or amino acid polymers. Preferably, the organic compound contains carbon and elements such as nitrogen, fluorine, phosphorus, and sulfur. After reduction, these elements can be incorporated into the carbon, improving the overall electronic conductivity of the composite cathode particles 200.

[0027] Specifically, carbon clusters 123 can be formed in the following ways: multiple carbon clusters formed by the dehydration of carbohydrates; carbon clusters containing multiple carbon skeletons and some functional groups formed by the dehydration of water-soluble fibers; and carbon clusters containing multiple straight-chain or branched carbon skeletons with doped elements formed by the dehydration of amino acid polymers.

[0028] The conductive layer 122 also contains a plurality of conductive carbon atoms 124 for connecting a plurality of carbon clusters 123, thereby further enhancing the overall conductivity.

[0029] The conductive carbon 124 is selected from at least one of graphite, graphene, nano-sized amorphous carbon, or carbon nanotubes with a length not exceeding 1 micrometer.

[0030] The plurality of lithium-ion conductor particles 10 are distributed inside the conductive layer 122, near the outside of the conductive layer 122, or near the outer surface of the LMFP particles 121.

[0031] The thickness of the conductive layer 122 is no greater than 200 nm, and the size of each lithium-ion conductor particle 10 is no greater than 200 nm.

[0032] The lithium-ion conductor particles 10 refer to: (i) Possesses lithium-ion conductivity (ionic conductivity greater than 10). -5 Oxides or phosphates with a density of (cm² / s), including but not limited to lithium aluminum titanium phosphate (LATP) and lithium aluminum germanium phosphate (LAGP) having a NASICON structure, or phosphates with lithium conductivity such as lithium phosphate; and (ii) Oxides having a garnet or perovskite structure, including but not limited to lithium lanthanum zirconium oxide (LLZO) or lithium lanthanum titanium oxide (LLTO).

[0033] The lithium-ion conductor particles 10 can also be a combination of the above components in any proportion.

[0034] The outer surface of the lithium-ion conductor particle 10 may also be coated with a borate layer 5 to form a lithium-ion composite conductor particle 101.

[0035] The lithium-ion composite conductor particles 101 are distributed on the LMFP particles 121 in a continuous manner or form island-shaped particles, which are naturally formed during the preparation process.

[0036] The purpose of coating the borate layer 5 is as follows: During the preparation of the composite cathode particles 200, oxygen-free sintering is required. In an oxygen-free environment, lithium-ion conductor particles 10 may develop lithium defects due to lack of oxygen, leading to a decrease in conductivity. Therefore, coating the outer surface of the lithium-ion conductor particles 10 with the borate layer 5 serves as a protective layer to prevent the structure of the lithium-ion conductor particles 10 from being damaged during the preparation process.

[0037] When the lithium-ion conductor particle 10 is selected as LLZO, the LLZO can be selected from: LLZO (Li7La3Zr2O) 12 At least one of the following: lithium lanthanum zirconium oxide), Ga-LLZO (Ga-doped LLZO), Cu-LLZO (Cu-doped LLZO), Ta-LLZO (Ta-doped LLZO), Sr-LLZO (Sr-doped LLZO), and Al-LLZO (Al-doped LLZO).

[0038] Preferably, LLZO is Cu a X b -LLZO, or lithium lanthanum zirconium oxide doped with copper and element X, wherein X is selected from Ga (gallium), Ta (tantalum), Sr (strontium), Ba (barium), and Al (aluminum), where a > 0 and b > 0. Preferably, a + b = 0.25~0.8, and a > 0.1. Doping LLZO with copper is a challenging process, but it results in a more stable particle structure, smoother lithium-ion channels, and increased oxygen sintering speed, reducing manufacturing costs. Simultaneously, it reduces the formation of lithium carbonate (Li₂CO₃) when LLZO is exposed to air, improving the overall surface stability of the structure during sintering.

[0039] When the lithium-ion conductor particle 10 is selected from LAGP or LATP, the LAGP or LATP is selected from Li 1+x Al x A 2-x (PO4)3 or Li 1+x+y Al x A 2-x-y-z M y N z (PO4)3, where x is between 0.1 and 0.8, y is between 0 and 0.2, z is between 0 and 0.2; A is Ge or Ti; M is a trivalent element and N is a tetravalent element.

[0040] M is a trivalent element, such as Sc. 3+ (Scandium), Y 3+ (Yttrium), Ga 3+ (GaN), In 3+ (Indium), La 3+ (Lanium), etc.; N is a tetravalent element, such as Zr.4+ (Zirconium), Si 4+ (Silicon), Sn 4+ (Tin), etc.

[0041] like Figure 4 As shown, the present invention can further improve conductivity by coating the composite cathode particles 200 with carbon material. The carbon material includes multiple carbon nanotubes 40 (CNTs) and multiple nanoscale amorphous carbon 45, which are coated on the outer surface of each composite cathode particle 200 to form a carbon-coated composite cathode particle 280.

[0042] The carbon nanotubes 40 include a plurality of short-chain carbon nanotubes 42 and a plurality of long-chain carbon nanotubes 44: the length of the short-chain carbon nanotubes 42 is between 0.2 μm and 1 μm; the length of the long-chain carbon nanotubes 44 is between 1 μm and 3 μm. The weight ratio of short-chain carbon nanotubes 42 to long-chain carbon nanotubes 44 is between 10:1 and 2:1.

[0043] The ratio of the total weight of carbon nanotubes 40 to the total weight of nanoscale amorphous carbon 45 is between 1:1 and 1:10. The size of nanoscale amorphous carbon 45 ranges from 10 nm to 40 nm.

[0044] The ratio of the total weight of carbon nanotubes 40 and nano-amorphous carbon 45 to the total weight of composite cathode particles 200 does not exceed 1:100.

[0045] Carbon nanotubes 40 of different lengths can form multi-layered bridging on the composite cathode particles 200: short-chain carbon nanotubes 42 bridging lithium-ion conductor particles 10 and their corresponding LMFP particles 121; long-chain carbon nanotubes 44 are used to completely coat the composite cathode particles 200 to enhance the overall structural strength.

[0046] When carbon nanotubes 40 are attached to composite cathode particles 200, they form a spherical structure similar to yarn.

[0047] The advantage of carbon nanotubes 40 is that lithium ions can exist stably between the carbon nanotubes 40, allowing the electrode slurry to stabilize a large number of lithium ions and improve the overall lithium ion conductivity. At the same time, electrons are also easily fixed between the carbon nanotubes 40, further improving the overall lithium ion conductivity. In addition, due to the extremely high ion conductivity, it helps the entire battery to achieve fast charging and fast discharging.

[0048] Nanoscale amorphous carbon 45, such as Super P conductive agent, is a conductive agent, just like carbon nanotubes 40. Since nanoscale amorphous carbon 45 is particulate while carbon nanotubes 40 are elongated, gaps are formed between the crisscrossing nanotubes 40. These gaps cannot conduct current. Therefore, adding nanoscale amorphous carbon 45 into these gaps allows charge to be conducted to the next carbon nanotube 40 through the bridging of the nanoscale amorphous carbon 45, thereby further improving current conduction efficiency.

[0049] Summary of the advantages of this invention: (1) A conductive layer is coated on the surface of LMFP particles to improve overall performance; (2) LMFP has a lower cost than ternary oxide batteries, making it suitable for specific scenarios and reducing battery production costs; (3) The conductive layer compensates for the insufficient conductivity of LMFP, and the lithium-ion conductor particles enhance the lithium conduction capability, thereby simultaneously improving conductivity and lithium-ion conduction capability and achieving better battery performance.

[0050] The foregoing detailed description pertains to one of the feasible embodiments of the present invention. However, this embodiment is not intended to limit the scope of the present invention. All equivalent implementations or modifications that do not depart from the spirit of the present invention should be included within the scope of the present invention.

Claims

1. A composite cathode particle of lithium manganese iron phosphate with high-strength conductive carbon, characterized in that, Used in the positive electrode of solid-state or near-solid-state batteries; the structure of the composite positive electrode particle includes: One lithium manganese iron phosphate particle, namely LMFP particle; A conductive layer is coated on the outer surface of the LMFP particle to form the composite cathode particle; the conductive layer contains multiple carbon clusters and multiple lithium-ion conductor particles to improve conductivity. The carbon clusters in the conductive layer are formed in any of the following ways: multiple carbon clusters formed by dehydration of carbohydrates; carbon clusters containing multiple carbon skeletons and some functional groups formed by dehydration of water-soluble fibers; carbon clusters containing multiple straight-chain or branched carbon skeletons with doped elements formed by dehydration of amino acid polymers. The plurality of lithium-ion conductor particles are distributed inside the conductive layer, near the outside of the conductive layer, or near the outer surface of the LMFP particles. The lithium-ion conductor particles are oxides or phosphates with lithium-ion conductivity, or oxides with a garnet / perovskite structure. The conductive layer also contains multiple conductive carbons, which are selected from at least one of graphite, graphene, nano-sized amorphous carbon, or carbon nanotubes with a length not exceeding 1 micrometer. These conductive carbons can connect carbon clusters in the conductive layer, enabling electrons to pass through different carbon clusters via the conductive carbons, thereby further improving the overall conductivity efficiency.

2. The lithium iron phosphate composite cathode particle with high-strength conductive carbon as described in claim 1, characterized in that, The carbohydrate is selected from at least one of monosaccharides, disaccharides, oligosaccharides, and polysaccharides.

3. The lithium iron phosphate composite cathode particle with high-strength conductive carbon as described in claim 1, characterized in that, in, The lithium-ion conductor particles have an ionic conductivity greater than 10. -5 Oxides or phosphates with a density of cm² / s, including lithium aluminum titanium phosphate, lithium aluminum germanium phosphate with a NASICON structure, or phosphates with lithium-ion conductivity; wherein lithium aluminum titanium phosphate is LAGP and lithium aluminum germanium phosphate is LATP.

4. The lithium iron phosphate composite cathode particle with high-strength conductive carbon as described in claim 1, characterized in that, in, The oxides having a garnet or perovskite structure include lithium lanthanum zirconium oxide or lithium lanthanum titanium oxide.

5. The lithium iron phosphate composite cathode particle with high-strength conductive carbon as described in claim 1, characterized in that, in, The median particle size distribution (D50) of the LMFP particles is less than 1 micrometer, and their morphology is a single crystal material or an aggregate of microcrystalline particles.

6. The lithium iron phosphate composite cathode particle with high-strength conductive carbon as described in claim 1, characterized in that, in, The LMFP particles are selected from lithium manganese iron phosphate, i.e., LiMnxFe 1-x PO4, x is between 0.1 and 0.8; or lithium manganese iron phosphate doped with at least one metal element.

7. The lithium iron phosphate composite cathode particle with high-strength conductive carbon as described in claim 1, characterized in that, in, The carbon clusters are compounds containing carbon and elements such as nitrogen, fluorine, phosphorus, and sulfur; after reduction, these elements can be incorporated into the carbon, thereby improving the overall electronic conductivity of the composite cathode particles.

8. The lithium iron phosphate composite cathode particle with high-strength conductive carbon according to claim 1, characterized in that, in, A borate layer is coated on the outer surface of the lithium-ion conductor particles to form lithium-ion composite conductor particles; the distribution of each lithium-ion composite conductor particle on the corresponding LMFP particle is either continuous or in the form of an island-like particle structure.

9. The lithium iron phosphate composite cathode particle with high-strength conductive carbon as described in claim 1, characterized in that, in, The thickness of the conductive layer is no greater than 200 nm; the size of each lithium-ion conductor particle is no greater than 200 nm.

10. The lithium iron phosphate composite cathode particle with high-strength conductive carbon according to claim 1, characterized in that, in, The lithium-ion conductor particles are composed of at least one of lithium lanthanum zirconium oxide, Ga-doped lithium lanthanum zirconium oxide, Cu-doped lithium lanthanum zirconium oxide, Ta-doped lithium lanthanum zirconium oxide, Sr-doped lithium lanthanum zirconium oxide, and Al-doped lithium lanthanum zirconium oxide.

11. The lithium iron phosphate composite cathode particle with high-strength conductive carbon as described in claim 1, characterized in that, in, The lithium-ion conductor particles are made of Cu a X b -LLZO formation, namely lithium lanthanum zirconium oxide doped with copper and element X; X is selected from at least one of Ga, Ta, Sr, Ba, Al, a>0 and b>0; this doping makes the particle structure more stable, the lithium ion channels smoother, and improves the oxygen sintering rate; at the same time, it can significantly reduce the formation of lithium carbonate (Li2CO3) when LLZO is exposed to air.

12. The lithium iron phosphate composite cathode particle with high-strength conductive carbon as described in claim 11, characterized in that, Among them, a+b=0.25~0.8, a>0.

1.

13. The lithium iron phosphate composite cathode particle with high-strength conductive carbon as described in claim 3, characterized in that, in, When the lithium-ion conductor particles are composed of LAGP or LATP, the LAGP or LATP is selected from Li 1+ x Al x A 2-x (PO4)3 or Li 1+x+y Al x A 2-x-y-z M y N z (PO4)3, where x is between 0.1 and 0.8, y is between 0 and 0.2, z is between 0 and 0.2; A is Ge or Ti; M is a trivalent element and N is a tetravalent element.

14. The lithium iron phosphate composite cathode particle with high-strength conductive carbon as described in claim 1, characterized in that, It also includes: multiple carbon nanotubes coated on the outer surface of each composite cathode particle to form composite cathode particles coated with carbon material.

15. The lithium iron phosphate composite cathode particle with high-strength conductive carbon as described in claim 14, characterized in that, in, The carbon material also includes multiple nanoscale amorphous carbons, the size of which is between 10 nanometers and 40 nanometers.

16. The lithium iron phosphate composite cathode particle with high-strength conductive carbon as described in claim 15, characterized in that, in, The plurality of carbon nanotubes includes a plurality of short-chain carbon nanotubes and a plurality of long-chain carbon nanotubes; the length of each short-chain carbon nanotube is between 0.2 micrometers and 1 micrometer, and the length of each long-chain carbon nanotube is between 1 micrometer and 3 micrometers.

17. The lithium iron phosphate composite cathode particle with high-strength conductive carbon as described in claim 16, characterized in that, in, The weight ratio of the plurality of short-chain carbon nanotubes to the plurality of long-chain carbon nanotubes is between 10:1 and 2:1; the ratio of the total weight of the plurality of carbon nanotubes to the total weight of the plurality of nanoscale amorphous carbons is between 1:1 and 1:

10.

18. The lithium iron phosphate composite cathode particle with high-strength conductive carbon according to claim 15, characterized in that, in, The nanoscale amorphous carbon is selected from Super P conductive agent and is used to bridge different carbon nanotubes to improve current transmission efficiency.

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