Lithium transition metal phosphate secondary agglomerates and process for its manufacture

Abstract

A Lithium-transition-metal-phosphate compound of formula Li.sub.0.9+xFe.sub.1-yM.sub.yPO.sub.4) in the form of secondary particles made of agglomerates of spherical primary particles wherein the primary particles have a size in the range of 0.02-2 pm and the secondary particles a mean size in the range of 10-40 pm and a BET surface of 16-40 m.sup.2/g, a process for its manufacture and the use thereof.

Claims

1. A lithium-transition-metal-phosphate compound of formula Li.sub.0.9+xFe.sub.1-yM.sub.y(PO.sub.4) with x0.3 and 0y1 and M is a metal or semimetal or mixtures thereof in the form of secondary particles made of agglomerates of spherical primary particles, wherein the primary particles have a size in the range of 0.02-2 m and the secondary particles have a mean size (d.sub.50) of 5-40 m and a BET surface of 16-40 m.sup.2/g and wherein the lithium-transition-metal-phosphate compound has a tap density of 1250-1600 g/l.

2. A lithium-transition-metal-phosphate compound of formula Li.sub.0.9+xFe.sub.1-yM.sub.y(PO.sub.4) with x0.3 and 0y1 and M is a metal or semimetal or mixtures thereof in the form of secondary particles made of agglomerates of spherical primary particles, wherein the primary particles have a size in the range of 0.02-2 m, wherein the secondary particles have a mean size (d.sub.50) of 5-40 m and a BET surface of 16-40 m.sup.2/g, wherein the lithium-transition-metal-phosphate compound has a tap density of 1250-1600 g/l and, wherein the lithium-transition-metal phosphate compound has a bulk porosity of 65-80%.

3. The lithium-transition-metal-phosphate compound according to claim 1 with a tap porosity of 55-65%.

4. The lithium-transition-metal-phosphate compound according to claim 1 with a bulk density of 750-1250 g/l.

5. The lithium-transition-metal-phosphate compound according to claim 1 with a press density of 2000-2800 g/l.

6. The lithium-transition-metal-phosphate compound according to claim 1 which is LiFePO.sub.4, LiMnPO.sub.4 or Li.sub.0.9+xFe.sub.1-yMn.sub.yPO.sub.4.

7. The lithium-transition-metal-phosphate compound according to claim 1, wherein the primary particles have a conductive carbon deposit on at least a part of the surface of the primary particles.

8. The lithium-transition-metal-phosphate compound according to claim 2 with a tap porosity of 55-65%.

9. The lithium-transition-metal-phosphate compound according to claim 2 which is LiFePO.sub.4, LiMnPO.sub.4 or Li.sub.0.9+xFe.sub.1-yMn.sub.yPO.sub.4.

10. The lithium-transition-metal-phosphate compound according to claim 2, wherein the primary particles have a conductive carbon deposit on at least a part of the surface of the primary particles.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) The invention is further explained by way of Figures and exemplary embodiments which are by no means meant to be limiting the scope of the invention.

(2) FIG. 1 is a SEM image of primary particles of unmilled CLiFePO.sub.4 obtained by a hydrothermal method,

(3) FIG. 2 is a SEM image of secondary agglomerates of unmilled CLiFePO.sub.4 obtained by spray drying without a milling step,

(4) FIG. 3 is a SEM image of the primary particles of the secondary agglomerates of CLiFePO.sub.4 of the invention milled with 1200 kWh/t,

(5) FIG. 4 is a SEM image of the secondary agglomerates of CLiFePO.sub.4 of the invention milled with 1200 kWh/t.

(6) FIG. 5 shows unmilled carbon coated LiFePO.sub.4 in powder form

(7) FIG. 6 shows another SEM photograph of secondary particles of CLiFePO.sub.4 according to the invention

(8) FIG. 7 shows the capacity of an electrode with CLiFePO.sub.4 according to the invention as active material

(9) FIG. 8A, FIG. 8B and FIG. 8C show the capacity upon cycling of prior art CLiFePO.sub.4 agglomerates of three different sources as active material

(10) FIG. 9 shows the capacity upon cycling of (unmilled) CLiFePO.sub.4 agglomerates of prior art

DETAILED DESCRIPTION OF THE INVENTION

(11) Experimental

(12) 1. General

(13) Determination of the Particle-Size Distribution:

(14) The particle-size distributions for the secondary agglomerates are determined using a light scattering method using commercially available devices. This method is known per se to a person skilled in the art, wherein reference is also made in particular to the disclosure in JP 2002-151082 and WO 02/083555. In this case, the particle-size distributions were determined by a laser diffraction measurement apparatus (Mastersizer 2000 APA 5005, Malvern Instruments GmbH, Herrenberg, Del.) and the manufacturer's software (version 5.40) with a Malvern dry powder feeder Scirocco ADA 2000. The setting of the refractive index of the material was 0.00 because the Fraunhofer data analysis method was used. The sample preparation and measurement took place according to the manufacturer's instructions. An air dispersion pressure of 0.2 bar was used.

(15) The D.sub.90 value gives the value at which 90% of the particles in the measured sample have a smaller or the same particle diameter according to the method of measurement. Analogously, the D.sub.50 value and the D.sub.10 value give the value at which 50% and 10% respectively of the particles in the measured sample have a smaller or the same particle diameter according to the method of measurement.

(16) According to a particularly preferred embodiment of the invention, the values mentioned in the present description are valid for the D.sub.10 values, D.sub.50 values, the D.sub.90 values as well as the difference between the D.sub.90 and D.sub.10 values relative to the volume proportion of the respective particles in the total volume. Accordingly, the D.sub.10, D.sub.50 and D.sub.90 values mentioned herein give the values at which 10 volume-% and 50 volume-% and 90 volume-% respectively of the particles in the measured sample have a smaller or the same particle diameter. If these values are obtained, particularly advantageous materials are provided according to the invention and negative influences of relatively coarse particles (with relatively larger volume proportion) on the processability and the electrochemical product properties are avoided. Preferably, the values mentioned in the present description are valid for the D.sub.10 values, the D.sub.50 values, the D.sub.90 values as well as the difference between the D.sub.90 and the D.sub.10 values relative to both percentage and volume percent of the particles.

(17) For compositions (e.g. electrode materials) which, in addition to the lithium-transition-metal phosphates according to the invention contain further components, in particular for carbon-containing compositions and electrode formulations, the above light scattering method can lead to misleading interpretations as the lithium-transition-metal phosphates secondary agglomerates can form further and larger agglomerates within the dispersion. However, the secondary particle-size distribution of the material according to the invention can be directly determined as follows for such compositions using SEM photographs:

(18) A small quantity of the powder sample is suspended in 3 ml acetone and dispersed with ultrasound for 30 seconds. Immediately thereafter, a few drops of the suspension are dropped onto a sample plate of a scanning electron microscope (SEM). The solids concentration of the suspension and the number of drops are measured so that a large single-ply layer of powder particles forms on the support in order to prevent the powder particles from obscuring one another. The drops must be added rapidly before the particles can separate by size as a result of sedimentation. After drying in air, the sample is placed in the measuring chamber of the SEM. In the present example, this is a LEO 1530 apparatus which is operated with a field emission electrode at 1.5 kV excitation voltage, an aperture of 30 m, an SE2 detector, and 3-4 mm working distance. At least 20 random sectional magnifications of the sample with a magnification factor of 20,000 are photographed. These are each printed on a DIN A4 sheet together with the inserted magnification scale. On each of the at least 20 sheets, if possible at least 10 free visible particles of the material according to the invention, from which the powder particles are formed together with the carbon-containing material, are randomly selected, wherein the boundaries of the particles of the material according to the invention are defined by the absence of fixed, direct connecting bridges. On the other hand, bridges formed by carbon material are included in the particle boundary. Of each of these selected particles, those with the longest and shortest axis in the projection are measured in each case with a ruler and converted to the actual particle dimensions using the scale ratio. For each measured Li.sub.0.9+xFe.sub.1-yM.sub.yPO.sub.4 particle, the arithmetic mean from the longest and the shortest axis is defined as particle diameter. The measured Li.sub.0.9+xFe.sub.1-yM.sub.yPO.sub.4 particles are then divided analogously to the light-scattering method into size classes. The differential particle-size distribution relative to the volume of particles is obtained by plotting the volume of the associated particles in each case against the size class. The volume of the associated particles V is approximated by the sum of the spherical volumes of each of these n particles V.sub.i calculated from their corresponding particle diameters d.sub.i:

(19) $V=\underset{i=1}{\overset{n}{.Math.}}{V}_i=\frac{}{6}\underset{i=1}{\overset{n}{.Math.}}{d}_i^3$

(20) The cumulative particle-size distribution from which D.sub.10, D.sub.50 and D.sub.90 can be read directly on the size axis is obtained by continually totaling the particle volumes from the small to the large particle classes.

(21) The described process was also applied to battery electrodes containing the material according to the invention. In this case, however, instead of a powder sample a fresh cut or fracture surface of the electrode is secured to the sample holder and examined under a SEM.

(22) BET measurements were carried out according to DIN-ISO 9277.

(23) Bulk density was determined according to ISO 697 (formerly DIN 53912).

(24) Tap density was measured according to ISO 787 (formerly DIN 53194).

(25) Press density and Powder Resistivity were measured at the same time with a combination of a Lorenta-CP MCP-T610 and a Mitsubishi MCP-PD 51 device. The Powder Resistivity is calculated according to formula:
Powder resistivity [cm]=resistance []thickness [cm]RCF (RCF=device dependent Resistivity Correction Factor)

(26) Pressure density was calculated according to the formula

(27) $\mathrm{Pressure}\mathrm{density}\left[g\text{/}{\mathrm{cm}}^3\right]=\frac{\mathrm{mass}\mathrm{of}\mathrm{sample}\left[g\right]}{.Math.r^2\left[{\mathrm{cm}}^2\right]\mathrm{thickness}\mathrm{of}\mathrm{the}\mathrm{sample}\left[\mathrm{cm}\right]}$

(28) The porosities were obtained from the corresponding measured densities according to the following formula:

(29) $\mathrm{Porosity}=\frac{1-\mathrm{density}}{\mathrm{true}\mathrm{material}\mathrm{density}}$
(the true material density was determined according to ISO 1183-1). For pure LiFePO.sub.4, the value is 3.56 kg/l.

(30) The SEM images taken with the LEO 1530 apparatus were recorded in tif file format at a resolution of 1024768. The mean primary particle diameter was measured as described in EP 2 413 402 Al for FE-SEM images.

(31) Spray drying was performed in a Nubilosa spray dryer 1.25 m in diameter, 2.5 m in cylindrical height and 3.8 m in total height. The spray dryer was equipped with pneumatic nozzles type 970 form 0 S3 with an open diameter of 1.2 mm and type 940-43 form 0 S2 with an open diameter of 1.8 mm both of Dsen-Schlick GmbH, Hutstrae 4, D-96253 Untersiemau, Germany. Drying gas was supplied by a controlled suction fan and heated electrically before entering the spray dryer. The dried particles were separated from the gas stream by a bag filter and recovered by a pulsed jet dedusting system. Amount of drying gas, gas inlet temperature and outlet temperature were controlled by a process control system. The outlet temperature control governed the speed of the slurry feed pump. Atomization gas was supplied by the compressed air distribution of the plant and its pressure was controlled by a local pressure controller.

(32) Pyrolysis was performed in a rotary kiln type LK 900-200-1500-3 of HTM Reetz GmbH, Kpenicker Str. 325, D-12555 Berlin, Germany. Its heated rotary tube was 150 mm in diameter and 2.5 m in length. It provided a preheating zone, three heated separately controlled temperature zones, and a cooling zone. The inclination of the tube could be adjusted and its rotational speed was variably controlled. Product was supplied by a controlled screw feeder. Product supply, the kiln itself and product outlet could be blanketed by nitrogen. The amount of pyrolyzed product could be continuously monitored by a balance.

(33) Milling was performed in an agitated ball mill MicroMedia P2 by Bhler AG, CH-9240 Uzwil, Switzerland, with SSiC ceramic cladding. It was filled with yttrium stabilized zirconium oxide beads of nominal 100 m (80-130 m) diameter. Its peripheral speed was controlled between 6.5 and 14.0 m/s. The milling compartment had a volume of 6.3 liter. The drive had a power rating of 30 kW. Heat was removed through the walls of its milling compartment by cooling water. The slurry to be milled was passed from an agitated vessel via a controlled peristaltic pump through the mill back to the vessel. This closed loop was operated until the desired specific milling energy had been reached.

(34) 2. Synthesis of the Primary Particles of Lithium Transition Metal Phosphates

(35) The lithium transition metal phosphates, for example LiFePO.sub.4 LiCoPO.sub.4, LiMnPO.sub.4, were obtained via hydrothermal synthesis according to WO2005/051840. The synthesis method can be applied to all lithium transition metal phosphates like Li.sub.0.9+xFe.sub.1-yMg.sub.y(PO.sub.4) Li.sub.0.9+xFe.sub.1-yNb.sub.y(PO.sub.4), Li.sub.0.9+xFe.sub.1-yCo.sub.y(PO.sub.4) Li.sub.0.9+xFe.sub.1-yZn.sub.y(PO.sub.4) Li.sub.0.9+xFe.sub.1-yAl.sub.y(PO.sub.4), Li.sub.0.9+xFe.sub.1-y(Zn, Mg).sub.y(PO.sub.4), Li.sub.0.9+xFe.sub.1-yMn.sub.y(PO.sub.4) as well.

(36) The term hydrothermal synthesis or conditions means for the purpose of the present invention temperatures of 100 C. to 200 C., preferably 100 C. to 170 C. and quite particularly preferably 120 C. to 170 C. as well as a pressure of 1 bar to 40 bar vapour pressure. In particular, it has surprisingly been shown that the synthesis at the quite particularly preferred temperature of 120-170 C., in particular at 1605 C., leads to an increase in the specific capacity of the thus-obtained Li.sub.0.9+xFe.sub.1-yM.sub.y(PO.sub.4) according to the invention compared with reaction at more than 160 C.5 C.

(37) The intermediate product is typically obtained in the form of a wet filter cake before preparing an aqueous suspension according to process step b).

(38) 3. Synthesis of the Lithium Transition Metal Phosphates in the Form of Secondary Agglomerates

Example 1: Preparation of Carbon Coated LiFePO.SUB.4 .Secondary Agglomerates

(39) The wet filter cake consisting essentially of carbon coated LiFePO.sub.4 primary particles (C-LFP) typically in form of needles and platelets is mixed with 10 mass-% of lactose (based on the solid lithium iron phosphate). A suspension with 52.5% solid content is prepared with distilled water to maximize the efficiency of the following milling step.

(40) The suspension is then continuously milled with a ball mill with grinding beads having a diameter of 90-110 m. The grinding beads consist of a stabilized zirconium oxide ceramic. The milling reactor was cladded with silicon carbide to avoid a contamination of the product and to allow an effective cooling.

(41) The energy introduced into the suspension is removed by cooling the suspension, wherein the main amount of the heat is directly removed by the mill.

(42) The mechanical energy applied to the suspension was 1200 kWh/t. During milling a total of 1.5 mass-% of citric acid (based on the solid lithium iron phosphate) were added.

(43) After milling the suspension was spray-dried via a pneumatic nozzle. The solid content of the suspension was 52.5%.

(44) During spray-drying the gas inlet temperature was 300 C., the outlet temperature was 105 C.

(45) The separation of the solid product from the gas was carried out in a bag filter. The dried agglomerate was further pyrolized in inert gas atmosphere at 750 C. in a rotary kiln.

(46) The product obtained had a bulk density of 1030 g/l, the tap density was 1480 g/l and the press density 2230 g/l.

(47) SEM images were recorded of the so obtained product (see FIGS. 3 and 4).

(48) The characteristics of this product were:

(49) TABLE-US-00002 Term Measured Unit Method Crystal >95% N/A XRD structure Olivine LiFePO.sub.4 Carbon-content 1.9 wt % C/S-Analyzer Mean particle size 71 nm SEM primary particles PSD (d.sub.10) 4.7 m Laser Diffraction (Malvern) PSD (d.sub.50) 15.9 m Laser Diffraction (Malvern) PSD (d.sub.90) 36.4 m Laser Diffraction (Malvern) Specific surface 19 m.sup.2/g Nitrogen adsorption (BET) area Bulk Density 1030 g/l Tap density 1480 g/l Automatic tap density analyzer Volume 13.9 cm Powder Resistivity Analyzer Resistivity Press Density 2.23 g/cm.sup.3 Powder Resistivity Analyzer pH value 9.5 pH electrode Spec. Capacity 158.4 mAh/g CLiFePO.sub.4/LiPF.sub.6 - EC-DMC/Li.sup.0 Charge/Discharge at C/10, 25 C. Range: 4.0 V-2.0 V

Example 2: Preparation of CLiMnPO.SUB.4 .Secondary Agglomerates

(50) The synthesis was carried out as in example 1. Instead of LiFePO.sub.4, LiMnPO.sub.4 was used.

(51) The product obtained had a bulk density of 1030 g/l, the tap density was 1400 g/l and the press density 2190 g/l. The BET-surface was 24 m.sup.2/g. The characteristics of this product were:

(52) TABLE-US-00003 Term Measured Unit Method Carbon-content 2.2 wt % C/S-Analyzer Mean particle size 85 nm SEM Primary particles PSD (d.sub.10) 3.6 m Laser Diffraction (Malvern) PSD (d.sub.50) 14.9 m Laser Diffraction (Malvern) PSD (d.sub.90) 30.5 m Laser Diffraction (Malvern) Specific surface 24 m.sup.2/g Nitrogen adsorption (BET) area Bulk Density 1030 g/l Tap Density 1400 g/l Automatic tap density analyzer Volume 25 cm Powder Resistivity Analyzer Resistivity Press Density 2.19 g/cm.sup.3 Powder Resistivity Analyzer pH value 8.8 pH electrode Spec. Capacity 150 mAh/g CLiMnPO.sub.4/LiPF.sub.6 - EC-DMC/Li.sup.0 Charge/Discharge at C/10, 25 C. Range: 4.3 V-2.0 V

Example 3: Preparation of CLiCoPO.SUB.4 .Secondary Agglomerates

(53) The synthesis was carried out as in example 1. Instead of LiFePO.sub.4, LiCoPO.sub.4 was used.

(54) The product obtained had a bulk density of 1050 g/l, the tap density was 1390 g/l and the press density 2180 g/l. The BET-surface was 25 m.sup.2/g. The characteristics of this product were:

(55) TABLE-US-00004 Term Measured Unit Method Carbon-content 2.0 wt % C/S-Analyzer Mean particle size 81 nm SEM Primary particles PSD (d.sub.10) 3.9 m Laser Diffraction (Malvern) PSD (d.sub.50) 15.1 m Laser Diffraction (Malvern) PSD (d.sub.90) 33.8 m Laser Diffraction (Malvern) Specific surface 25 m.sup.2/g Nitrogen adsorption (BET) area Bulk Density 1050 g/l Tap Density 1390 g/l Automatic tap density analyzer Volume 26 cm Powder Resistivity Analyzer Resistivity Press Density 2.18 g/cm.sup.3 Powder Resistivity Analyzer pH value 9.1 pH electrode Spec. Capacity 150 mAh/g CLiCoPO.sub.4/LiPF.sub.6 - EC-DMC/Li.sup.0 Charge/Discharge at C/10, 25 C. Range: 5.2 V-3.0 V

Example 4: Preparation of CLiMn.SUB.0.67.Fe.SUB.0.33.PO.SUB.4 .Secondary Agglomerates

(56) The synthesis was carried out as in example 1. Instead of LiFePO.sub.4, LiMn.sub.0.67Fe.sub.0.33PO.sub.4 was used.

(57) The product obtained had a bulk density of 1020 g/l, the tap density was 1430 g/l and the press density 2210 g/l. The BET-surface was 27 m.sup.2/g. The characteristics of this product were:

(58) TABLE-US-00005 Term Measured Unit Method Carbon-content 2.3 wt % C/S-Analyzer Mean primary 70 nm SEM particle size PSD (d.sub.10) 2.5 m Laser Diffraction (Malvern) PSD (d.sub.50) 13.8 m Laser Diffraction (Malvern) PSD (d.sub.90) 31.8 m Laser Diffraction (Malvern) Specific surface 27 m.sup.2/g Nitrogen adsorption (BET) area Bulk Density 1020 g/l Tap Density 1430 g/l Automatic tap density analyzer Volume 18 cm Powder Resistivity Analyzer Resistivity Press Density 2.21 g/cm.sup.3 Powder Resistivity Analyzer pH value 8.7 pH electrode Spec. Capacity 151 mAh/g CLiMn.sub.0.67Fe.sub.0.33PO.sub.4/LiPF.sub.6 - EC-DMC/Li.sup.0 Charge/Discharge at C/10, 25 C. Range: 4.3 V-2.0 V
4. Preparation Electrodes:

(59) Electrodes were prepared by mixing 90 parts per weight of lithium-transition-metal-phosphate of the invention or carbon coated lithium-transition-metal-phosphate together with 5 parts of carbon. 5 parts of a binder were diluted in N-methyl-2-pyrrolidon solution and added to the mixture. The mixture was kneaded to give a slurry. The slurry was applied by a doctoral blade to an aluminium collector foil serving as a collector. The film was dried at 60 C. under reduced pressure of 500 mbar for 2 h.

(60) A platen press was used for densification. But any other press like for example a calander press is suitable as well. The pressing force was in the range of from 500 to 10000 N/cm.sup.2, preferably 5000 to 8000 N/cm.sup.2. The target value for the coating (active material) packing density was >1.5 g/cm.sup.3 or higher, more preferably >1.9 g/cm.sup.3.

(61) The electrodes were dried for 2 more hours under vacuum, preferably at elevated temperatures of about 100 C. Cells were assembled as coffee bag cells (batteries), which consist of an aluminium coated polyethylene bag. Lithium metal was used as the counter electrode. 1M LiPF.sub.6 was used as electrolyte in a 1:1 mixture of ethlylenecarbonate (EC):diethylenecarbonate (DEC). In each battery one layer of a microporous polypropylene-foil (Celgard 2500; Celgard 2500 is a trademark) having lithium ion permeability was used as the separator. The bags were sealed using a vacuum-sealing machine.

(62) Measurements were performed in a temperature-controlled cabinet at 20 C. using a Basytec cell test system (CTS). Voltage range for cycling was between 2.0V and 4.0V for pure LiFePO.sub.4. For other cathode materials the voltage had to be adjusted according to the voltage profile of the system, e.g. for LiFe.sub.0.33Mn.sub.0.67PO.sub.4 between 4.3 and 2.0 V.

(63) FIG. 1 is a SEM image of primary particles of unmilled CLiFePO.sub.4 of prior art obtained by a hydrothermal method (WO 2005/051840 A1. The platelet shape of the fine crystals can be seen.

(64) FIG. 2 is a SEM image of secondary agglomerates of unmilled CLiFePO.sub.4 obtained by spray drying without a milling step, i.e. secondary agglomerates obtained from the primary particles as shown in FIG. 1. The irregular shape is clearly visible.

(65) FIG. 3 is a SEM image of the primary particles of the secondary agglomerates of CLiFePO.sub.4 of the invention milled with 1200 kWh/t and FIG. 4 is a SEM image of the secondary agglomerates of CLiFePO.sub.4 of the invention milled with 1200 kWh/t. The differences in particle size and morphology are clearly visible. The properties with respect to density are described above.

(66) FIG. 4 shows CLiFePO.sub.4 agglomerates according to the invention (example 1) with mean particle sizes of 10-20 m (d.sub.50=15.9), having a higher density, better flowability and less dusting than the powders of the prior art as can be seen from the figures and their homogeneous particle morphology.

(67) FIG. 5 shows primary particles of CLiFePO.sub.4 according to the invention. In comparison to FIG. 1 it is clearly visible that the primary particles of CLiFePO.sub.4 agglomerates of the prior art are much coarser.

(68) FIG. 6 shows another SEM photograph of secondary particles of CLiFePO.sub.4 according to the invention. The secondary particle size of 15-20 m facilitates the electrode processability, namely enables that a homogeneous dispersion of the particles of the active material/conductive agent/binder within the electrode can be obtained. With active material of the prior art, either in agglomerate or powder form inhomogeneities are observed which deteriorate the cycling characteristics and the capacity of the electrode. Further uncontrolled formation of locally concentrated agglomerates of active material is avoided. Thus an electrode according to the invention shows a higher capacity and conductivity than electrodes with active material of the prior art. The agglomerates according to the invention are more stable towards external pressure than agglomerates of prior art. It was observed that during processing of the electrode formulation (preparation of a dispersion and applying to an electrode substrate) 95% of the agglomerates according to the invention remained intact, whereas the more brittle agglomerates of the prior art remained only to 50% intact.

(69) FIG. 7 above shows the capacity of an electrode with carbon coated LiFePO.sub.4 (C-LFP) according to the invention made in accordance with example 1 as active material, indicating excellent cycling characteristics. The electrode formulation was 90/5/5 weight parts CLiFePO.sub.4 (carbon coated LiFePO.sub.4)/Super P Li carbon/Binder PVDF 21216. The electrode density was 1.7 g/cm.sup.3, the loading was 4.35 mg/cm.sup.2.

(70) FIG. 8 shows the capacity upon cycling of prior art carbon coated LiFePO.sub.4 agglomerates of three different sources. The electrode formulation was 90/5/5 weight parts CLiFePO.sub.4/Super P Li carbon/Binder PVDF 21216. The electrodes were prepared as described in the foregoing and FIG. 7.

(71) As can be seen compared to FIG. 7 and table 1, all prior art material showed inferior electrochemical properties.

(72) FIG. 9 shows the capacity upon cycling of carbon coated LiFePO.sub.4 agglomerates of prior art (LFP-prior art) obtained according to the combined teachings of WO 2005/051840 A1 and US 2010/0233540 (see below)(unmilled). Also here, the electrochemical properties of CLiFePO.sub.4 according to the invention proved to be superior (see in FIG. 7 and table 1). The material of sources A, B, C were obtained from Hanwha Chemicals (C-LFP: grade LFP-1000) (source B), VSPC Co. Ltd. (C-LFP, grade: generation 3) (source C) or were made according to US 2010/0233540 (C-LFP, source A). The Agglomerates C-LFP Prior Art were obtained by synthesizing LFP primary particles according to WO 2005/051840 A1 followed by spray drying according to the process described in US 2010/0233540.

(73) The following summarizes the electric properties of the materials in FIGS. 7-9. It can be seen that C-LFP according to the invention is better than the prior art materials A, B and C and C-LFP agglomerates prior art and has better processability with a better flowability and less dusting and more homogeneous distribution in the electrode formulation.

(74) TABLE-US-00006 TABLE 1 Electric properties of material according to the invention and of prior art C-LFP Discharge Agglomerates Agglomerates Agglomerates Agglomerates C-LFP Rate Unit of source A of source B of source C prior art invention Capacity C/10 mAh/g 148.5 156.4 150.4 153.4 158.4 1 C mAh/g 141.2 143.1 139.4 144.2 153.3 3 C mAh/g 129.8 132.6 127.4 134.0 145.5 5 C mAh/g 125.4 126.2 119.6 127.4 140.1 10 C mAh/g 115.0 116.1 105.7 114.0 128.6 Volumetric C/10 mWh/cm.sup.3 998 898 923 960 1048 Energy 1 C mWh/cm.sup.3 926 804 836 875 1000 Density 3 C mWh/cm.sup.3 816 729 742 781 924 5 C mWh/cm.sup.3 770 675 679 719 870 10 C mWh/cm.sup.3 666 587 574 605 760 Press kg/m.sup.3 2030 1810 2000 1915 2060 Density PSD d10 m 7.8 0.92 5.8 4.5 4.7 d50 m 25.4 6.1 15.0 14.8 15.9 d90 m 58.0 17.1 28.0 30.8 36.4