Lithium manganese iron phosphate composite cathode particles

Abstract

We provide lithium manganese iron phosphate composite cathode particles. [Solution] The structure of the composite positive electrode particles comprises LMFP particles and a conductive layer covering the outer surface of the LMFP particles. The conductive layer contains a plurality of carbon aggregates and a plurality of lithium ion conductor particles. The plurality of carbon aggregates are formed by dehydrating carbohydrates, water-soluble fibers, or amino acid polymers. The plurality of lithium ion conductor particles are distributed inside the conductive layer, close to the outside of the conductive layer, or close to the outer surface of the LMFP particles. The lithium ion conductor particles are oxides or carbonates having lithium ion conducting ability, or garnet or oxides having a perovskite structure.

Description

[Technical Field]

[0001] This invention relates to a positive electrode material for batteries, and more particularly to lithium manganese iron phosphate composite positive electrode particles. [Background technology]

[0002] A battery consists of a positive electrode and a negative electrode, with the cathode being the positive electrode inside the battery. The positive electrode of a typical all-solid-state or semi-solid-state battery mainly comprises a positive electrode substrate and a positive electrode slurry layer, the positive electrode slurry layer containing positive electrode slurry and positive electrode particles. The positive electrode particles need to be conductive or conductive in order to allow free electrons to move within the positive electrode slurry and to prevent excessive energy loss due to internal resistance. As the material for the positive electrode particles, LMFP (lithium manganese iron phosphate) may be selected, as it has better operating voltage performance than lithium iron phosphate (LFP), releases energy at a higher energy density, is inexpensive, and is hydrophobic. [Overview of the project] [Problems that the invention aims to solve]

[0003] However, LMFPs have poor multiplier charge / discharge performance, low lithium guiding ability, and low conductivity, and their structure deteriorates quickly when used in batteries for extended periods. While many technologies already exist to improve the guiding ability of positive electrode particles to lithium ions, their conductivity is still insufficient for practical use.

[0004] Therefore, as a result of diligent research, the inventors have found that the above objective can be achieved by having a positive electrode of an all-solid-state battery with higher capacity and conductivity.

[0005] This invention has been made in view of these circumstances, and its purpose is to provide lithium manganese iron phosphate composite cathode particles.

[0006] To solve the above problems, the present invention employs the following means. Lithium manganese iron phosphate composite cathode particles according to one aspect of the present invention enhance overall performance by coating the outside of the LMFP particles with a conductive layer. LMFP has a lower cost than ternary oxides, and its charge / discharge performance is applicable to a specific range, allowing for a reduction in battery manufacturing costs when used as a cathode material. The conductive layer coating the outer surface of the LMFP particles compensates for the disadvantage of low conductivity of LMFP, and further coating the outer surface of the LMFP particles with multiple lithium ion conductor particles enhances the overall lithium guide ion capability, thereby improving overall conductivity and lithium guide ion capability, and achieving even better battery performance.

[0007] The following information will become clear from the description in the specification and drawings described later. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view showing composite cathode particles according to one embodiment of the present invention. It is an explanatory diagram showing [the particle]. [Figure 2] This is an example of lithium manganese iron phosphate composite cathode particles according to the present invention. [Figure 3] A schematic diagram and an enlarged view showing composite cathode particles according to one embodiment of the present invention. [Figure 4] This is a schematic diagram showing composite cathode particles coated with a carbon material according to one embodiment of the present invention. [Figure 5] This is a schematic diagram showing lithium-ion composite conductive particles according to one embodiment of the present invention. [Figure 6] This is another example demonstrating lithium-ion composite conductive particles according to the present invention. [Modes for carrying out the invention]

[0009] The present invention will be described below through embodiments of the invention, but these embodiments are not intended to limit the invention as defined in the claims. Furthermore, not all combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0010] First, referring to FIGS. 1 to 6, an embodiment of the lithium manganese iron phosphate composite positive electrode particles according to the present invention will be described.

[0011] The lithium manganese iron phosphate composite positive electrode particles according to the present invention are used for the positive electrode 100 of all-solid or semi-solid batteries. The positive electrode 100 mainly includes a positive electrode substrate 105 (see FIG. 2) and a positive electrode slurry layer 108 coated on the positive electrode substrate 105. The positive electrode slurry layer 108 includes a positive electrode slurry 103 having a binder and a plurality of composite positive electrode particles 200. The weight percentage of the total weight of the plurality of composite positive electrode particles 200 in the positive electrode slurry layer 108 is in the range of 88 wt% to 98 wt%.

[0012] FIG. 1 shows the configuration of each composite positive electrode particle 200 according to an embodiment of the present invention. It mainly includes the following configurations.

[0013] The D50 particle diameter (mass-median-diameter, MMD, the mass median particle diameter of the particle size distribution) of the LMFP particles 121 is less than 1 μm, and its form is a single crystal material or a polymer of fine crystal particles.

[0014] The LMFP particles 121 are composed of lithium manganese iron phosphate (LiMn x Fe 1-x PO4, where X is in the range of 0.1 to 0.8) or lithium manganese iron phosphate doped with at least one metal element.

[0015] By coating the outer surface of the LMFP particles 121 with the conductive layer 122, the overall composite positive electrode particles 200 are formed. The conductive layer 122 includes a plurality of carbon aggregates 123 and a plurality of lithium ion conductor particles 10, and is used to enhance conductivity (see FIG. 1). Each carbon aggregate 123 is formed from a carbon source added during the process of the composite positive electrode particles 200.

[0016] [[ID=,30]] The carbon aggregates 123 of the conductive layer 122 are capable of forming organic compounds of carbon in a reducing atmosphere. The organic compounds are selected from carbohydrates (e.g., monosaccharides, disaccharides, oligosaccharides, polysaccharides), water-soluble fibers, or amino acid polymers. Preferably, the organic compounds are compounds containing carbon and elements such as nitrogen, fluorine, phosphorus, and sulfur, and after generating a reduction reaction, these elements are doped into the carbon to enhance the overall electronic conductivity of the composite cathode particles 200.

[0017] The plurality of carbon aggregates 123 of the conductive layer 122 are either a plurality of carbon aggregates formed by dehydrating carbohydrates, a plurality of carbon skeletons and partial functional groups formed by dehydrating water-soluble fibers, or a plurality of carbon skeletons having straight chains or side chains of dopants formed by dehydrating amino acid polymers.

[0018] The conductive layer 122 further comprises multiple conductive carbon 124s that link the multiple carbon aggregates 123 and allow electrons to cross over different carbon aggregates 123 by the conductive carbon 124s, thereby enhancing overall conductivity. The multiple conductive carbon 124s are formed from one of the following: graphite, graphene, nano-sized amorphous carbon, or carbon nanotubes with a length of 1 μm or less (see Figure 6).

[0019] The multiple lithium-ion conductor particles 10 are distributed inside the conductive layer 122, close to the outside of the conductive layer 122, or close to the outer surface of the LMFP particles 121. The thickness of the conductive layer 122 is 200 nm or less. The size of each lithium-ion conductor particle 10 is 200 nm or less.

[0020] The lithium ion conductor particles 10 have lithium ion conductivity (ionic conductivity is 10 -5 cm 2The oxide or carbonate having a lithium ion conductivity of more than 1 / s, or an oxide having a garnet or perovskite structure. Examples of oxides or carbonates having lithium ion conductivity include lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), which have a NASICON (sodium (Na) superionic conductor) structure, or phosphates such as lithium phosphate (Li3PO4) which have lithium conductivity. Examples of oxides having a garnet or perovskite structure include lithium lanthanum zirconium oxide (Li7La3Zr2O). 12 These include lithium lanthanum zirconium oxide (LLZO) and lithium lanthanum titanium oxide (LLTO). The lithium ion conductor particles 10 may also be a combination of the above components in any ratio.

[0021] The outer surface of each lithium-ion conductor particle 10 may be further coated with a boric acid layer 5 to form lithium-ion composite conductor particles 101. The distribution morphology of each lithium-ion composite conductor particle 101 in the LMFP particles 121 may be a continuous distribution morphology, a discontinuous distribution morphology, or an island particle morphology, which is a structure that is naturally formed during the process.

[0022] The purpose of coating the outer surface of the lithium ion conductor particles 10 with the boric acid layer 5 is that, in the manufacturing process of the composite positive electrode particles 200, the lithium in the lithium ion conductor particles 10 becomes depleted due to oxygen deficiency in an oxygen-free sintering environment, resulting in a decrease in conductivity. By coating the outer surface of the lithium ion conductor particles 10 with the boric acid layer 5 to form a protective layer, the situation in which the structure of the lithium ion conductor particles 10 is destroyed is prevented.

[0023] Each of the lithium ion conductor particles 10 is formed of an LLZO material, and the LLZO material is formed of at least one of LLZO, Ga-LLZO (Ga-doped LLZO, gallium-doped lithium lanthanum zirconium oxide), Cu-LLZO (Cu-doped LLZO, copper-doped lithium lanthanum zirconium oxide), Ta-LLZO (Ta-doped LLZO, tantalum-doped lithium lanthanum zirconium oxide), Sr-LLZO (Sr-doped LLZO, strontium-doped lithium lanthanum zirconium oxide), and Al-LLZO (Al-doped LLZO, aluminum-doped lithium lanthanum zirconium oxide).

[0024] Preferably, the LLZO material is Cu a ,X b -LLZO, and the Cu a ,X b -LLZO is a lithium lanthanum zirconium oxide doped with copper and element X, X is selected from gallium (Ga), tantalum (Ta), strontium (Sr), barium (Ba), and aluminum (Al), and a > 0 and b > 0. Preferably, it is in the range of a + b = 0.25 to 0.8, and a > 0.1. Although the technique of doping copper into LLZO is very difficult, the overall structure is more stable, the channels for lithium ions are smoother, the sintering rate is improved, and the manufacturing cost is very low. Also, when the LLZO material is exposed to air, the formation of lithium carbonate (Li2CO3) is reduced, that is, the stability of the surface of the whole material during sintering is enhanced.

[0025] When the lithium ion conductor particles 10 are composed of LAGP or LATP, the LAGP or LATP is 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 zSelected from (PO4)3, x is in the range of 0.1 to 0.8, y is in the range of 0 to 0.2, and z is in the range of 0 to 0.2. A is Ge (germanium) or Ti (titanium). M is Sc 3+ (Scandium ion), Y 3+ (Yttrium ion), Ga 3+ (Gallium ion), In 3+ (Indium ion), La 3+ (Lanthanum ion) is a trivalent cation. N is Zr 4+ (Zirconium ion), Si 4+ (Silicon ions), Sn 4+ These are tetravalent cations such as (tin ions).

[0026] In the example shown in Figure 4, the present invention enhances conductivity by coating the outer surface of the composite cathode particles 200 with a carbon material. The carbon material comprises a plurality of carbon nanotubes 40 (CNT) and a plurality of nanoscale amorphous carbon 45, and by coating the outer surface of the composite cathode particles 200, composite cathode particles 280 coated with the carbon material are formed.

[0027] The plurality of carbon nanotubes 40 according to the present invention include a plurality of short-chain carbon nanotubes 42 and a plurality of long-chain carbon nanotubes 44, wherein the length of each short-chain carbon nanotube 42 is in the range of 0.2 μm to 1 μm, and the length of each long-chain carbon nanotube 44 is in the range of 1 μm to 3 μm. The weight ratio of the plurality of short-chain carbon nanotubes 42 and the plurality of long-chain carbon nanotubes 44 is in the range of 10:1 to 2:1. The weight ratio of the total weight of the plurality of carbon nanotubes 40 and the total weight of the plurality of nanoscale amorphous carbon 45 is in the range of 1:1 to 1:10. The size of the nanoscale amorphous carbon 45 is in the range of 10 nm to 40 nm. The weight ratio of the "total weight of the plurality of carbon nanotubes 40 and the plurality of nanoscale amorphous carbon 45" and the total weight of the composite cathode particles 200 is 1:100 or less, that is, the weight ratio value is 0.01 or less.

[0028] The carbon nanotubes 40 of different lengths form crosslinks of varying numbers on the composite cathode particles 200. The short-chain carbon nanotubes 42 can crosslink each of the lithium-ion conductor particles 10 and the LMFP particles 121. The long-chain carbon nanotubes 44 are used to coat the entire composite cathode particles 200 and increase its overall structural strength. When multiple carbon nanotubes 40 adhere to the composite cathode particles 200, a ball-like structure is formed.

[0029] The advantage of the carbon nanotube 40 is that lithium ions are easily stabilized among the carbon nanotube 40, so the electrode slurry according to the present invention becomes stable as a very large number of lithium ions, increasing the overall conductivity of lithium ions, and electrons are easily fixed among the carbon nanotube 40, further increasing the overall conductivity of lithium ions. In addition, because the ion conductivity is very high, it helps in the high-speed charging and discharging of the entire battery.

[0030] The nanoscale amorphous carbon is, for example, a super P conductive agent. Both the nanoscale amorphous carbon 45 and the carbon nanotubes 40 are conductive agents. The nanoscale amorphous carbon 45 has a particle form, and the carbon nanotubes 40 have an elongated form. The nanoscale amorphous carbon 45 fills the gaps between multiple carbon nanotubes 40 that intersect vertically and horizontally, and the nanoscale amorphous carbon 45 is crosslinked, allowing charge to be conducted to other carbon nanotubes 40, further increasing the efficiency of current transmission.

[0031] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0032] 5. Boric acid layer 10 Lithium-ion conductor particles 40 Carbon nanotubes 42 Short-chain carbon nanotubes 44 Long-chain carbon nanotubes 45 nanoscale amorphous carbon 100 positive electrode 101 Lithium-ion composite conductive particles 105 Positive electrode substrate 103 Positive electrode slurry 108 Cathode slurry layer 121 LMFP particles 122 Conductive layer 123 Carbon aggregates 124 Conductive carbon 200 composite cathode particles 280 Composite cathode particles coated with carbon material

Claims

1. Lithium manganese iron phosphate composite positive electrode particles used in the positive electrode of an all-solid or semi-solid battery, wherein the composite positive electrode particles are LMFP particles and, A conductive layer covering the outer surface of the LMFP particles, wherein the conductive layer comprises a plurality of carbon aggregates and a plurality of lithium ion conductor particles, Each of the carbon aggregates in the conductive layer is a plurality of carbon aggregates formed by dehydrating carbohydrates, a plurality of carbon aggregates containing a carbon skeleton and partial functional groups formed by dehydrating water-soluble fibers, or a plurality of carbon aggregates having a linear or branched carbon skeleton containing a dopant formed by dehydrating an amino acid polymer. The plurality of lithium-ion conductor particles are distributed inside the conductive layer, close to the outside of the conductive layer, or close to the outer surface of the LMFP particles. The lithium manganese iron phosphate composite cathode particles are characterized in that the lithium ion conductor particles are oxides or carbonates having lithium ion conductivity, or oxides having a garnet or perovskite structure.

2. The lithium manganese iron phosphate composite cathode particles according to claim 1, characterized in that the carbohydrate is selected from monosaccharides, disaccharides, oligosaccharides, and polysaccharides.

3. The lithium ion conductor particles have an ionic conductivity of 10 －５ cm ２ The lithium manganese iron phosphate composite cathode particle according to claim 1, characterized in that it comprises the oxide or carbonate having a s ratio greater than / s, and includes lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), or a phosphate having lithium conductivity, having a NASICON (sodium (Na) super ionic conductor) structure.

4. The lithium manganese iron phosphate composite cathode particle according to claim 1, characterized in that the oxide having a garnet or perovskite structure includes lithium lanthanum zirconium oxide (LLZO) or lithium lanthanum titanium oxide (LLTO).

5. The lithium manganese iron phosphate composite cathode particle according to claim 1, characterized in that the median mass particle diameter in the particle size distribution of the LMFP particles is less than 1 μm, and its form is a single-crystal material or a polymer of fine crystalline particles.

6. The LMFP particles are lithium manganese iron phosphate (LiMnxFe １ -xPO ４ The lithium manganese iron phosphate composite cathode particle according to claim 1, characterized in that it is composed of lithium manganese iron phosphate doped with at least one metallic element (where X is in the range of 0.1 to 0.8).

7. The lithium manganese iron phosphate composite cathode particle according to claim 1, characterized in that the carbon aggregate is a compound containing carbon and elements such as nitrogen, fluorine, phosphorus, and sulfur, and is doped so that the nitrogen, fluorine, phosphorus, and sulfur penetrate the carbon.

8. The lithium manganese iron phosphate composite cathode particle according to claim 1, characterized in that the outer surface of each lithium ion conductor particle is coated with a boric acid layer to form a lithium ion composite conductor particle, and each lithium ion composite conductor particle exhibits a continuous distribution, a discontinuous distribution, or an island particle configuration in the LMFP particle.

9. The lithium manganese iron phosphate composite cathode particle according to claim 1, characterized in that the thickness of the conductive layer is 200 nm or less, and the size of each lithium ion conductor particle is 200 nm or less.

10. The lithium manganese iron phosphate composite cathode particle according to claim 1, characterized in that each of the lithium ion conductor particles is formed of an LLZO material, and the LLZO material is formed of at least one of LLZO, Ga-LLZO (Ga-dope LLZO, gallium-doped lithium lanthanum zirconium oxide), Cu-LLZO (Cu-dope LLZO, copper-doped lithium lanthanum zirconium oxide), Ta-LLZO (Ta-dope LLZO, tantalum-doped lithium lanthanum zirconium oxide), Sr-LLZO (Sr-dope LLZO, strontium-doped lithium lanthanum zirconium oxide), and Al-LLZO (Al-dope LLZO, aluminum-doped lithium lanthanum zirconium oxide).

11. Each of the lithium ion conductor particles is Cu ａ , X ｂ - Composed of LLZO, the Cu ａ , X ｂ -LLZO is a lithium lanthanum zirconium oxide doped with copper and element X, wherein X is selected from gallium (Ga), tantalum (Ta), strontium (Sr), barium (Ba), and aluminum (Al), and a > 0 and b > 0, characterized in that the lithium manganese iron phosphate composite cathode particle according to claim 1.

12. The lithium manganese iron phosphate composite cathode particle according to claim 11, characterized in that a + b = 0.25 to 0.8 and a > 0.

1.

13. Each of the lithium ion conductor particles is formed of LAGP or LATP, and the LAGP or the LATP is i １＋ｘ Al ｘ A ２－ｘ (PO ４ ) ３ or Li １＋ｘ＋ｙ Al ｘ A ２－ｘ－ｙ－ｚ M ｙ N ｚ (PO ４ ) ３ selected from, x is in the range between 0.1 and 0.8, y is in the range between 0 and 0.2, z is in the range between 0 and 0.2, A is germanium (Ge) or titanium (Ti), M is a trivalent cation, and N is a tetravalent cation. The lithium manganese iron phosphate composite positive electrode particles according to claim 1, characterized in that

14. The lithium manganese iron phosphate composite cathode particle according to claim 1, characterized in that the outer surface of the composite cathode particle is further coated with a carbon material, the carbon material further comprises a plurality of carbon nanotubes and a plurality of nanoscale amorphous carbon, the size of the nanoscale amorphous carbon being in the range of 10 nm to 40 nm.

15. The lithium manganese iron phosphate composite cathode particle according to claim 14, characterized in that the plurality of carbon nanotubes comprises a plurality of short-chain carbon nanotubes and a plurality of long-chain carbon nanotubes, the length of each short-chain carbon nanotube being in the range of 0.2 μm to 1 μm, and the length of each long-chain carbon nanotube being in the range of 1 μm to 3 μm.

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