Surface preparation of natural graphite and the effect of impurities on grinding and the particle distribution

a technology of natural graphite and impurities, which is applied in the field of surface preparation of natural graphite and the effect of impurities on grinding and particle distribution, can solve the problems of reducing the mobility and maximum concentration of lithium batteries inside the layers, and slowing the arrival of lithium batteries in the classical formats (aa, c, d, etc.) to the public at larg

Inactive Publication Date: 2005-09-22
HYDRO QUEBEC CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

This major problem has slowed the arrival of lithium batteries in the classical formats (AA, C, D, etc.) to the public at large.
The lithium thus inserted has, moreover, a more substantial mass and apparent volume, which reduces its mobility as well as its maximum concentration inside the layers.
In addition, in propylene carbonate medium, the ternary compound is very unstable, the solvent reacts to become gaseous propene that can cause a violent degradation of the battery.
Electricity consumed during this step cannot be recovered when the current is inverted.
The faraday output of this first cycle is therefore poor.
The graphite used conventionally as electrode material in a lithium-ion battery is generally obtained from two distinct sources: synthetic graphite or natural thermally highly purif

Method used

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  • Surface preparation of natural graphite and the effect of impurities on grinding and the particle distribution
  • Surface preparation of natural graphite and the effect of impurities on grinding and the particle distribution
  • Surface preparation of natural graphite and the effect of impurities on grinding and the particle distribution

Examples

Experimental program
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Effect test

example 1

[0049] A natural graphite having an initial particle size of 375 μm is ground by a process of air milling until the particle size reaches 10 μm. The size of the main particles obtained (50% distribution of particles or D50%) is 10.52 μm. The Gaussian distribution of graphite has only one maximum and no additional peak. The granulometric distribution was determined with the aide of a Microtrac™ particle analyser built and sold by Leeds & Northrul. The methanol was used as the carrier fluid. Subsequently, the ground graphite was leached in an aqueous bath of 30% HF. The temperature of the mixture is maintained at 90° C., with a leached time of 180 minutes. The graphite is then filtered, washed with copious amounts of water, and the powder dried for a period of 24 hours at 120° C.

[0050] The graphite powder obtained is analysed by reversed diffusion coupled with EDX (Energy Dispersive X-ray). No exfoliation of the particles was observed. In addition the analysis by EDX shows that the m...

example 2

[0054] Natural graphite having an initial particle size of 375 μm is ground by a process of air-milling until the particles attain a size of 10 μm. The graphite is then leached in a mixed aqueous bath comprising 30% H2SO4 and 30% HF. 106.5 ml of the mixed acid is heated to 90° C., and 30 g of graphite is then added into the solution. The graphite is leached for 180 minutes in a reactor. The solid is then filtered, washed with copious amounts of water, and dried at 120° C. for 24 hours. The size (D50%) is 10.92 μm, and this before and after purification. The Gaussian distribution for the graphite has only one single maximum without any peak.

[0055] The analysis of impurities in the graphite by EDX shows mainly the presence of the elements Ca and F. Analysis of the impurities of the residual ashes shows the graphite purity to be 99.68%. The electrode preparation and the electrochemical tests are done using the same procedure described in example 1.

[0056] The coulombic efficiency of t...

example 3

[0057] The natural graphite used in this example is processed in an identical manner as that described in Example 2, with the exception that the HF concentration is now 20%. Analysis of the impurities in the graphite by EDX shows the main presence of the elements Ca and F. The analysis of the impurities of the residual ashes shows the graphite to have a purity of 99.75%. The preparation of the electrode and the electrochemical tests were conducted with the identical procedures described in example 1.

[0058] The coulombic efficiency of the first cycle is 89%. The irreversible plateau due to the passivating layer is formed normally near 800 mV. The reversible capacity of the graphite is 365 mAh / g, equivalent to x=0.98 for the formation LixC6.

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Abstract

The present invention relates to the physical or chemical specific purification of natural mineral graphite. This purification is preferably applied to the surface of natural graphite in order to allow the formation of a passivation film during the first electrical discharge or the insertion of lithium in the graphite when the latter is used in a lithium-ion cell. The grinding to a small size before purification allows the optimization of the distribution of the particles, resulting in a more uniform electrode. This grinding is carried out in the presence of the natural impurities of the graphite that play the role of a micro-abrasive and result in a hardness of the graphite that increases its mechanical properties.

Description

FIELD OF INVENTION [0001] The present invention relates to the physical and chemical purification specific to the mineral of natural graphite with the goal of generating a purified graphite which is particularly advantageous for use in carbon-lithium anodes. This purification is applied preferentially to the surface of natural graphite to permit the formation of a passivating layer with the first electrical discharge or insertion of lithium in the graphite when the graphite is used in a lithium-ion battery. Grinding to a very small size before the purification permits the optimisation of the size distribution of the particles, which gives rise to an electrode which is much more homogenous. This grinding is done in the presence of the natural impurities of the graphite which play a role as a micro abrasive and give a hardness to the graphite which increases its mechanical properties. It goes without saying that the purified graphite particles can have many other usages, notably in th...

Claims

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Application Information

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IPC IPC(8): C01B31/04H01M4/133H01M4/58H01M4/583H01M10/0525H01M10/36
CPCC01B31/0407H01M4/133Y02E60/122H01M10/0525H01M4/583C01B32/215Y02E60/10
Inventor ZAGHIB, KARIM
Owner HYDRO QUEBEC CORP
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