Recycled Graphite Purification for Li-Ion Battery Anodes
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Solution Overview
Problem
Conventional recycling methods for lithium-ion batteries fail to achieve the required purity of graphite anode material, often leaving substantial impurities such as aluminum oxide, nickel, manganese, and cobalt oxides, which hinder the production of high-performance anode materials.
Innovation Solution
A method involving the use of an aqueous sodium hydroxide solution to remove aluminum oxide and silicon oxide from graphite, followed by a hydrochloric acid treatment to eliminate remaining impurities, and subsequent coating with amorphous carbon and heat treatment to achieve purity levels of 99.5% or higher.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional recycling methods are used to recover graphite from spent Li-ion batteries, then graphite can be recovered, but the recovered graphite contains substantial impurities such as aluminum oxide, nickel, manganese, and cobalt oxides
Solution Approach 1:
The purification process is divided into multiple sequential stages: (1) magnetic separation to remove ferromagnetic impurities, (2) flotation to separate aluminum oxide, (3) leaching to remove nickel, manganese, and cobalt oxides, and (4) filtration to remove remaining particulates. Each stage targets specific impurity types, progressively increasing graphite purity to battery-grade levels (99.5% or higher).
Solution Approach 2:
The patent systematically extracts different impurity classes from recovered graphite using specialized techniques: magnetic separation extracts ferromagnetic particles, flotation extracts aluminum oxide through surface property differences, and chemical leaching extracts transition metal oxides. This multi-extraction approach isolates graphite from all major impurity categories present in conventional recycling outputs.
2Manufacturing precision
If multiple purification steps are implemented to achieve high purity graphite, then graphite purity improves to 99.5% or higher, but process complexity increases
Solution Approach 1:
The patent combines multiple purification functions into an integrated processing line where magnetic separation, flotation, leaching, and filtration operations are sequentially arranged and operationally linked. This merged system processes graphite through all purification stages in a continuous flow, achieving high purity while managing complexity through systematic integration rather than separate isolated operations.
Solution Approach 2:
The leaching stage utilizes controlled parameter changes to selectively remove impurities: acid concentration, temperature, and reaction time are optimized to dissolve nickel, manganese, and cobalt oxides while leaving graphite intact. This parameter-based selectivity enables high purity achievement through chemical differentiation rather than mechanical separation complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively purifies graphite to meet or exceed 99.5% purity, addressing the impurity issues in conventional recycling and enhancing the performance characteristics of recycled anode materials.
Implementation Method 1
treating the impure graphite with an aqueous solution comprised of sodium hydroxide for a time, at specified temperature and pressure to extract a first portion of impurities
Implementation Method 2
treating the graphite with a second aqueous solution comprising hydrochloric acid for a time and at a temperature to extract a second portion of metals and oxides from the impure graphite
Implementation Method 3
heat treated for a time and temperature
Data Source
AI summary
A method to recycle graphite from lithium and sodium-ion batteries. Graphite from the batteries first is treated in an aqueous solution of strong base at a temperature range between about 100° C. and about 250° C., a pressure range between about 0.9 bar and about 20 bar, at a solid-to-liquid ratio of from about 1-to-1 to about 1-to-4. The treated graphite is then washed, filtered, and then treated with a mineral acid (e.g., hydrochloric acid). The purified graphite is then coated with amorphous carbon at a weight percentage range between 0.5 wt % and about 20 wt %. The recycled graphite yielded by the method routinely achieves a purity >99.9%, a specific area of less than or equal to about 10 m2/g.