Expanded Graphite Anode for High-Capacity Lithium-Ion Batteries
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Solution Overview
Problem
Conventional lithium-ion battery anodes based on carbonaceous materials face limitations in achieving high reversible capacity and long cycle life due to irreversible lithium loss and high charge transfer resistance, particularly in amorphous carbon phases, which restricts energy density and efficiency.
Innovation Solution
A carbonaceous material with an interplanar spacing of at least 0.400 nm, derived from graphite or graphite-based compounds, is used as the anode in lithium secondary batteries, allowing for expanded interstitial spaces to accommodate multiple lithium layers, enhancing specific capacity and cycle stability through deep oxidation or fluorination treatments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If amorphous carbon phase is used to increase specific capacity beyond 372 mAh/g, then reversible capacity is improved, but charge transfer resistance increases and electrical conductivity decreases
Solution Approach 1:
The patent employs a composite carbonaceous material comprising both crystalline graphite phases and amorphous carbon phases. The crystalline graphite provides good electrical conductivity and low charge transfer resistance, while the amorphous carbon phase contributes to enhanced specific capacity beyond the theoretical limit of graphite. This composite structure allows the material to achieve reversible capacities greater than 372 mAh/g while maintaining acceptable charge transfer characteristics.
2Stability of the object's composition
If conventional graphite intercalation compound LixC6 is used, then theoretical specific capacity is limited to 372 mAh/g, but structural stability is maintained
Solution Approach 1:
The patent modifies the structural parameters of graphite by controlling the interlayer spacing (d002) to be at least 0.400 nm, which is larger than the conventional graphite spacing of approximately 0.335 nm. This parameter change creates expanded interstitial spaces that can accommodate additional lithium ions beyond the standard LixC6 stoichiometry, enabling specific capacities exceeding 372 mAh/g while preserving the fundamental graphite crystal structure and its stability.
3Reliability
If SEI layer is formed during first several cycles, then protective interface is created, but irreversible lithium loss occurs reducing energy density
Solution Approach 1:
The patent employs preliminary surface treatment methods including oxidation and fluorination to pre-modify the carbonaceous material surface before battery assembly. These treatments create a controlled surface chemistry that promotes the formation of a stable, thin SEI layer during initial cycling. The pre-treated surface reduces the amount of lithium consumed during SEI formation, thereby minimizing irreversible capacity loss while ensuring adequate protective interface formation.
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
The carbonaceous material achieves specific capacities greater than 500 mAh/g, with improved cycle life and reduced irreversible capacity loss, exceeding theoretical limits and demonstrating superior performance in lithium-ion batteries.
Implementation Method 1
lithium ions are adsorbed on two sides of a single graphene sheet
Implementation Method 2
graphite that can be intercalated with lithium and the resulting graphite intercalation compound may be expressed as LixC6
Data Source
AI summary
A lithium secondary battery comprising a positive electrode, a negative electrode comprising a carbonaceous material which is capable of absorbing and desorbing lithium ions, and a non-aqueous electrolyte disposed between the negative electrode and the positive electrode. The carbonaceous material comprises a graphite crystal structure having an interplanar spacing d002 of at least 0.400 nm (preferably at least 0.55 nm) as determined from a (002) reflection peak in powder X-ray diffraction. This larger interplanar spacing implies a larger interstitial space between two graphene planes to accommodate a greater amount of lithium. The battery exhibits an exceptional specific capacity, excellent reversible capacity, and long cycle life.