阅读说明：本技术 锂金属磷酸盐、其制备和用途 (Lithium metal phosphates, their preparation and use ) 是由 卢多维克·布里克特 玛丽亚·里瓦斯-维拉兹科 诺莉娅·卡贝洛-莫雷诺 马赫雷斯·阿姆里 于 2019-09-13 设计创作，主要内容包括：本发明提供了一种锂过渡金属磷酸盐材料,其包含掺杂有非常精确量的铝掺杂物的磷酸铁锂,该材料具有式Li-yFe-(1-x)Al-xPO-4,其中0.8≤y≤1.2且0.0120≤x≤0.0180。当x处于该范围内时,可改善所述材料的容量,并且观察到铝在锂金属磷酸盐中的良好或优异分布。(The invention providesA lithium transition metal phosphate material comprising lithium iron phosphate doped with a very precise amount of an aluminum dopant, the material having the formula Li y Fe 1‑x Al x PO 4 Wherein y is more than or equal to 0.8 and less than or equal to 1.2, and x is more than or equal to 0.0120 and less than or equal to 0.0180. When x is within this range, the capacity of the material can be improved and a good or excellent distribution of aluminum in the lithium metal phosphate is observed.)

1. A carbon-coated particulate lithium metal phosphate having the formula

Li_yFe_1-xAl_xPO₄

Wherein y is more than or equal to 0.8 and less than or equal to 1.2, and x is more than or equal to 0.0120 and less than or equal to 0.0180.

2. The carbon-coated particulate lithium metal phosphate of claim 1, wherein 0.0130 ≦ x ≦ 0.0170.

3. The carbon-coated particulate lithium metal phosphate according to claim 1 or claim 2, wherein 0.9. ltoreq. y.ltoreq.1.1.

4. The carbon-coated particulate lithium metal phosphate according to any one of the preceding claims, having the formula LiFe_{1- x}Al_xPO₄。

5. The carbon-coated particulate lithium metal phosphate of any one of the preceding claims, wherein the lithium metal phosphate has a crystallite size of 60nm or greater as determined by Rietveld analysis.

6. The carbon-coated particulate lithium metal phosphate according to any one of the preceding claims, which is prepared by a solid state process.

7. A process for the preparation of a carbon-coated particulate lithium metal phosphate according to the invention, which process comprises

(i) A grinding step in which a lithium-containing precursor, an iron-containing precursor, an aluminum-containing precursor, and a carbon-containing precursor are mixed and ground; and

(ii) a calcination step in which the product of the milling step is calcined to obtain the carbon-coated particulate lithium metal phosphate.

8. The method of claim 7, wherein the milling step is a high energy milling step.

9. The method of claim 7 or claim 8, wherein the aluminum-containing precursor is Al₂O₃Or Al (OH)₃Preferably Al (OH)₃。

10. The method of any one of claims 7 to 9, further comprising forming an electrode comprising the carbon-coated lithium metal phosphate.

11. The method of claim 10, further comprising constructing a battery including the electrode.

12. Carbon-coated particulate lithium metal phosphate obtained or obtainable by a process according to any one of claims 7 to 9.

13. Use of the carbon-coated particulate lithium metal phosphate according to any one of claims 1 to 6 and 12 in the preparation of an electrode for a secondary lithium ion battery.

14. An electrode for a secondary lithium ion battery comprising the carbon-coated particulate lithium metal phosphate according to any one of claims 1 to 6 and 12.

15. A secondary lithium ion battery comprising the electrode of claim 14.

Technical Field

The present invention relates to lithium transition metal phosphate materials, their preparation and use as cathode materials in secondary lithium ion batteries.

Background

Lithium metal phosphates having an olivine-type structure have emerged as promising cathode materials in secondary lithium ion batteries. The advantages of lithium metal phosphates compared to other lithium compounds include the fact that: it is relatively environmentally friendly and has excellent safety characteristics during battery handling and operation.

Melt processes, hydrothermal processes and solid state processes are the most common synthetic routes for the preparation of lithium metal phosphates.

The relatively poor electrochemical performance of lithium metal phosphates has been attributed to their poor electronic conductivity, and their performance has been significantly improved by coating the particles with conductive carbon.

There remains a need for lithium metal phosphates that can be made by simple, cost-effective and scalable processes, employ low cost precursors, and exhibit comparable or improved electrochemical performance.

Disclosure of Invention

The inventors have found that the electrochemical performance of lithium iron phosphate can be improved by adding a very precise amount of aluminum dopant. Thus, in a first preferred aspect, the present invention provides a carbon-coated particulate lithium metal phosphate having the formula

Li_yFe_1-xAl_xPO₄

Wherein y is more than or equal to 0.8 and less than or equal to 1.2, and x is more than or equal to 0.0120 and less than or equal to 0.0180.

The inventors have found that when x is in this range, the capacity of the material can be improved and a good or excellent distribution of aluminium in the lithium metal phosphate is observed.

It may be preferred that the carbon-coated lithium metal phosphate is prepared by a solid state process. For example, the method may involve grinding, such as high energy grinding. Thus, in a second preferred aspect, the present invention provides a process for the preparation of a carbon-coated particulate lithium metal phosphate according to the invention, said process comprising

(i) A grinding step in which a lithium-containing precursor, an iron-containing precursor, an aluminum-containing precursor, and a carbon-containing precursor are mixed and ground; and

(ii) a calcination step in which the product of the milling step is calcined to obtain the carbon-coated particulate lithium metal phosphate.

The present invention also provides a carbon-coated lithium metal phosphate obtainable by or obtainable by the process of the second aspect.

In a further preferred aspect, the present invention provides the use of a carbon-coated lithium metal phosphate according to the invention for the preparation of a cathode for a secondary lithium ion battery. In a further preferred aspect, the present invention provides a cathode comprising the carbon-coated lithium metal phosphate of the present invention. In a further preferred aspect, the invention provides a secondary lithium ion battery comprising a cathode comprising the carbon-coated lithium metal phosphate of the invention. The battery also typically includes an anode and an electrolyte.

Drawings

Fig. 1A shows a TEM image of the sample prepared in example 1, and fig. 1B shows the distribution of aluminum in the sample.

Fig. 2A shows a TEM image of the sample prepared in example 4, and fig. 2B shows the distribution of aluminum in the sample.

Fig. 3A shows a TEM image of the sample prepared in example 5, and fig. 3B shows the distribution of aluminum in the sample.

Fig. 4 shows the electrochemical performance of the samples of examples 1, 2, 3 and 4.

Fig. 5 shows the relationship between the specific capacity and Al content at 3C and 10C for examples 1, 2, 3 and 4.

Fig. 6 shows the electrochemical performance of the samples of examples 5, 6 and 7.

Fig. 7 shows the relationship between the specific capacity and Al content at 3C and 10C for examples 5, 6 and 7.

Detailed Description

Preferred and/or optional features of the invention will now be set out. Any aspect of the invention may be combined with any other aspect of the invention, unless the context requires otherwise. Any preferred and/or optional features of any aspect may be combined with any aspect of the invention, alone or in combination, unless the context requires otherwise.

The invention provides a carbon-coated particulate lithium metal phosphate having the formula

Li_yFe_1-xAl_xPO₄

Wherein y is more than or equal to 0.8 and less than or equal to 1.2, and x is more than or equal to 0.0120 and less than or equal to 0.0180.

The value of y is greater than or equal to 0.8. It may be greater than or equal to 0.9, or greater than or equal to 0.95. The value of y is less than or equal to 1.2. It may be less than or equal to 1.1, or less than or equal to 1.05. The value of y can be 1 or about 1.

The value of x is greater than or equal to 0.0120. It may be greater than or equal to 0.0130, or greater than or equal to 0.0135. The value of x is less than or equal to 0.0180. It may be less than or equal to 0.0170, less than or equal to 0.0160, less than or equal to 0.0150, or less than or equal to 0.0145. The value of x may be 0.014, 0.0140, or about 0.014.

The stoichiometry of the lithium metal phosphate is generally calculated with reference to the starting materials from which it is prepared, taking into account the yield of the preparation reaction and the purity of the starting materials. In solid state preparation processes, the yield is typically at or very near 100%. For this calculation, it may be appropriate to assume a yield of 100% with respect to Fe and optionally Al and/or Li.

Carbon-coated lithium metal phosphates are typically prepared by a process comprising a milling step and a calcination step. The milling step may preferably be a high energy milling step. The milling step may be a dry milling step or may be a wet milling step, for example in the presence of a liquid such as water or an organic solvent. Suitable organic solvents include isopropanol, glycol ethers, acetone and ethanol.

The term "high energy milling" is a term well known to those skilled in the art that is distinguished from milling or grinding processes that deliver a lesser amount of energy. For example, high energy milling is understood to refer to a milling process in which at least 100kWh of energy per kilogram of solids being milled is delivered during the milling process. For example, at least 150kWh or at least 200kWh per kilogram of solids being milled can be delivered. There is no particular upper limit on this energy, but it may be less than 500kWh, less than 400kWh, or less than 350kWh per kilogram of solids being ground. Energy in the range of 250kWh/kg to 300kWh/kg may be typical. The grinding energy is generally sufficient to cause mechanochemical reaction of the ground solid.

In the milling step, a lithium-containing precursor, an iron-containing precursor, an aluminum-containing precursor, and a carbon-containing precursor are mixed and milled. The nature of each precursor is not limited in the present invention. If phosphorus is not provided as part of one of the iron, lithium or aluminum precursors added in the milling step, a separate phosphorus-containing precursor (e.g., a phosphate-containing precursor) is typically added. In the case of the wet milling step, spray drying may be performed between the milling step and the calcination step.

Suitable lithium-containing precursors include lithium carbonate (Li)₂CO₃) Lithium hydrogen phosphate (Li)₂HPO₄) And lithium hydroxide (LiOH). Li₂CO₃May be preferred.

Suitable iron-containing precursors include iron phosphate (FePO)₄) And ferrous oxalate. The iron phosphate may be hydrated (e.g., FePO)₄.2H₂O) orMay be dehydrated. FePO₄May be preferred.

The D50 particle size of the iron-containing precursor may be about 4 μm, for example in the range of 0.5 μm to 15 μm. The D50 particle size may be at least 1 μm or at least 2 μm. It may be less than 10 μm, less than 6 μm, less than 5 μm or less than 4.5 μm. The iron phosphate may have a D10 particle size of about 1.5 μm, for example 0.5 μm to 3 μm. The iron phosphate may have a D90 particle size of about 8 μm, for example 5 μm to 10 μm, for example 6 μm to 9 μm.

Suitable aluminum-containing precursors include aluminum hydroxide (Al (OH)₃) Aluminum chloride (AlCl)₃) And alumina (Al)₂O₃)。Al(OH)₃May be preferred because the present inventors have found that a material prepared using the aluminum-containing precursor may have a higher capacity and exhibit excellent aluminum dispersibility.

Typically, the aluminum, iron, lithium (and optionally phosphorus) precursors are mixed in appropriate proportions to obtain the desired stoichiometry for the lithium metal phosphate product.

The nature of the carbon-containing precursor is not particularly limited in the present invention. The carbon precursor is typically a carbon-containing compound that decomposes into carbonaceous residues upon exposure to the calcination step. For example, the carbon-containing precursor can be one or more of the following: starch, maltodextrin, gelatin, polyols, sugars such as mannose, fructose, sucrose, lactose, glucose, galactose and carbon based polymers such as polyacrylates, polyvinyl acetate (PVA) and polyvinyl butyrate (PVB). Alternatively, the carbonaceous precursor may be elemental carbon, such as one or more of graphite, carbon black, acetylene black, carbon nanotubes, and carbon fibers (such as vapor grown carbon fibers, VGCF). In some embodiments, PVB may be preferred.

The amount of the carbon precursor added is not particularly limited in the present invention. For example, the amount of carbon precursor may be selected to obtain a carbon content of 1 to 5 wt%, such as 2 to 3 wt%, in the carbon-coated lithium metal phosphate. The amount of carbon precursor added in the milling step may be in the range of 3 to 15 wt%, for example 3 to 7 wt%, depending on the nature of the carbon precursor and its carbonation yield.

The lithium metal phosphate may have a crystallite size of at least 60nm as determined by Rietveld analysis of XRD data. The upper limit of the crystallite size is not particularly limited, but may be 500nm or less, 200nm or less, 100nm or less, 80nm or less, or 70nm or less. The observed larger crystallite size may indicate a higher degree of crystallinity and fewer crystal defects, which may enhance lithium ion conduction within the lithium metal phosphate material, thereby enhancing electrochemical performance.

In the calcination step, the product of the milling step is typically calcined under an inert atmosphere to obtain the carbon-coated particulate lithium metal phosphate. The calcination step performs two functions. First, it causes pyrolysis of the carbon precursor to form a conductive carbon coating on the lithium metal phosphate particles. Secondly, it causes the lithium metal phosphate formed to crystallize into the desired olivine-type structure. Typically, the calcination is carried out in an inert atmosphere, for example in an inert gas such as argon. Alternatively, it may be carried out in a reducing atmosphere.

It is typically carried out at a temperature in the range 550 ℃ to 800 ℃, for example 600 ℃ to 750 ℃, or 600 ℃ or 650 ℃ to 700 ℃. 680 c is particularly suitable. Typically, the calcination is carried out for a period of 3 to 24 hours. The calcination time depends on the manufacturing scale (i.e., in the case of preparing larger amounts, longer calcination times may be preferred). For example, on a commercial scale, 8 to 15 hours may be suitable.

The method of the invention may further comprise the step of forming an electrode (typically a cathode) comprising the carbon-coated lithium metal phosphate. Typically, this is done by: forming a slurry of carbon-coated particulate lithium metal phosphate, applying the slurry to the surface of a current collector (e.g., an aluminum current collector), and optionally processing (e.g., calendaring) to increase the density of the electrode. The slurry may comprise one or more of a solvent, a binder, and additional carbon material.

The method of the invention may further comprise constructing a battery or electrochemical cell comprising an electrode comprising carbon-coated lithium metal phosphate. The battery or cell also typically includes an anode and an electrolyte. The battery or cells may typically be secondary (rechargeable) lithium ion batteries.

The invention will now be described with reference to the following examples, which are provided to aid understanding of the invention and are not intended to limit the scope of the invention.

Examples

For all synthetic examples, comparative examples and LFP reference samples, the following procedure was followed. The following table 1 shows the formulation of the prepared lithium iron phosphate, and the type and amount of each precursor.

Mixing Li₂CO₃、FePO₄Aluminum hydroxide from Sigma Aldrich (99.9%), and PVB (as carbon source) were mixed in the desired ratio to give 50mmol LiFePO₄The stoichiometric composition of (a). The materials were placed into 250ml ZrO together with 3mm YSZ spheres₂In a container. The sphere/metal oxide weight ratio is equal to 10/1. The solids were then ground (400rpm) in a planetary mill (high energy mill) for 3 h. Milling was performed over a period of 20 minutes with 10 breaks in between (i.e., the sample was allowed to effectively mill for 120 minutes).

The sample was calcined at 680 ℃ for 5 hours under argon to form olivine-type lithium iron phosphate coated with conductive carbon.

TABLE 1

"comparative" indicates comparative examples.

Table 2 below summarizes the stoichiometric amounts of Fe and Al in the products of the above examples.

TABLE 2

XRD analysis

XRD of all samples shows that olivine type lithium iron phosphate is a main phase, and a small amount of Li appears along with the increase of Al content₃PO₄. By passingThe crystallite sizes determined by Rietveld analysis are shown in table 3 below.

TABLE 3

Using Al (OH)₃Having Al produced as an aluminium precursor_0.014Doped example 1 has a significantly larger crystallite size.

Table 4 shows the occupancy of aluminum ions at lithium and iron sites in an olivine-type structure, as determined by Reitveld refinement.

TABLE 4

These data show that most of the aluminum ions occupy the iron ion sites in the lithium iron phosphate olivine-type structure.

The lattice volume of the unit cell for each sample as determined by XRD analysis is shown in table 5 below, to the three decimal places. The numbers in parentheses represent the error of the third digit after the decimal point. The unit cell volume of the LFP reference without Al is also shown.

TABLE 5

The reduction in lattice volume of the unit cell compared to the LFP reference without Al supports the following conclusions: most of the aluminum ions occupy the iron sites in the olivine-type iron phosphate structure.

TEM analysis

The samples of examples 1, 4 and 5 were examined using TEM. Fig. 1A shows a TEM image of the sample prepared in example 1, and fig. 1B shows the distribution of aluminum in the sample. The distribution of Al is excellent.

Fig. 2A shows a TEM image of the sample prepared in example 4, and fig. 2B shows the distribution of aluminum in the sample. The distribution of Al is poor.

Fig. 3A shows a TEM image of the sample prepared in example 5, and fig. 3B shows the distribution of aluminum in the sample. The distribution of Al is moderate.

Electrochemical analysis

The samples prepared in the above examples were used to form electrodes. The electrode coating formulation has a solids content of about 40% by weight. The solid fraction consisted of 90% by weight of the active material from the respective examples, 5% by weight of carbon black (from Imerys)^TMC65) 5% by weight of binder (Solef 5130)^TM(polyvinylidene fluoride, 10% by weight binder in N-methyl pyrrolidone)). The coating formulation was used to cast electrodes on 20 μm aluminum foil using a vacuum coater to obtain 5mg/cm²Electrode loading (electrode loading refers to the loading of the active material on the electrode). The coated electrode was calendered to give 2.0g/cm³Is the overall density of the electrode, including the active material, carbon black and binder. The electrode was then dried at 120 ℃ for 12 hours.

Forming an electrochemical coin cell (available from Hohsen)^TM2032 coin cell). The electrolyte is from Solvonic^TMLP30 of (1M LiPF6 in a 1:1 weight ratio mixture of dimethyl carbonate and ethylene carbonate. The anode was 0.75mm thick lithium and the separator was a glass microfiber filter (Whatman)^TMGF/F). The pressure used to crimp the coin cell was 750 psi.

The electrochemical performance of each sample was measured using a voltage window of 4.0V to 2.0V. The results of the electrochemical analysis are shown in fig. 4, 5, 6 and 7.

FIG. 4 shows samples of examples 1, 2, 3 and 4 (with Al (OH))₃Preparation) of the electrochemical properties. The sample of example 1 exhibited the highest specific capacity at all C rates tested. Fig. 5 shows the relationship between specific capacity and Al content for these examples at 3C and 10C, indicating that an aluminum content of about 0.014 provides a capacity significantly higher than 0.01, 0.027 and 0.055.

FIG. 6 shows samples (with Al) of examples 5, 6 and 7₂O₃Preparation) of the electrochemical properties. The sample of example 5 exhibited the highest specific capacity at all C rates tested. Fig. 7 shows the relationship between specific capacity and Al content for these examples at 3C and 10C, indicating that an aluminum content of about 0.014 provides a capacity significantly higher than 0.027 and 0.055.