Recycled Graphite Purification by Iterative Roasting and Washing
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Solution Overview
Problem
Conventional recycling methods for lithium-ion batteries struggle to achieve high purity graphite for anode material due to residual impurities like aluminum oxide, which complicates meeting customer specifications for performance and physical characteristics.
Innovation Solution
A two-phase roasting process combined with washing, involving multiple iterations of sintering with hydroxide-based solutions and subsequent washing with DI water and optional acid wash, effectively converts water-insoluble metal impurities into water-soluble forms for removal, achieving graphite purity of at least 99.5%.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional leaching and washing processes are used to recover graphite from spent Li-ion batteries, then the recovery process is simple and fast, but the graphite product contains substantial impurities like aluminum oxide that fail to meet battery-grade purity specifications
Solution Approach 1:
The purification process is divided into multiple sequential stages: initial leaching, first roasting with acid wash, second roasting with base wash, and optional third roasting. Each stage targets specific impurities and progressively increases graphite purity from ~80% to 99.5% or higher, breaking down the complex purification challenge into manageable steps.
Solution Approach 2:
The process utilizes parameter changes by alternating between acidic and basic chemical environments during different roasting stages. The pH conditions are systematically varied to selectively dissolve different types of impurities, with each roasting-washing cycle optimizing chemical parameters to remove specific contaminants while preserving graphite.
2Manufacturing precision
If multiple roasting and washing cycles are implemented to achieve high purity graphite, then impurity removal is effective, but the processing time and operational complexity increase
Solution Approach 1:
The initial leaching stage performs preliminary removal of soluble cathode materials and loosely bound impurities before the main roasting cycles. This preliminary action reduces the impurity load entering the subsequent roasting stages, making the overall process more efficient and reducing the time required for later purification steps.
Solution Approach 2:
The process employs periodic alternation between roasting (heating) and washing (cooling/chemical treatment) cycles. This periodic action allows impurities to be converted to soluble forms during roasting, then removed during washing phases, creating an efficient rhythm of impurity transformation and removal that accelerates overall purification.
3Quantity of substance
If acid leaching is used to recover graphite from black mass, then cathode materials are effectively extracted, but aluminum oxide and other metal impurities remain as residues in the graphite product
Solution Approach 1:
The process selectively extracts different components at different stages: initial acid leaching extracts cathode materials (Ni, Mn, Co), while subsequent base washing extracts aluminum oxide and other metal impurities from the graphite. Each extraction stage targets specific substances, separating them systematically from the graphite product.
Solution Approach 2:
The roasting process acts as an intermediary that transforms insoluble metal impurities into water-soluble metal salts or hydroxides. This chemical transformation mediates between the initial mixed impurity state and the final purified graphite state, enabling efficient removal of aluminum oxide and other contaminants through subsequent washing.
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 approach significantly improves the purity of recycled graphite, achieving up to 99.9% purity and meeting stringent battery-grade standards, enhancing the quality and performance of recycled anode material.
Implementation Method 1
A roasting process iterates multiple times for purifying the graphite, combined with washing, and is believed to convert water insoluble metal impurities into water-soluble metal salts
Implementation Method 2
Removal of the metal salts in the graphite occurs by leaching in a dilute sodium hydroxide solution and washing the purified graphite for further removal of the water-soluble impurities
Data Source
AI summary
A method of producing a purified graphite from a recycled battery stream for use in as anode material in Li-ion batteries is described. The method comprises a leaching step to obtain a precipitate comprising graphite by filtration, which is then iteratively roasted as a slurry with an aqueous solution of a hydroxide base and subsequently washed to form a purified graphite.