Halogen-Intercalated Graphite Cathode for Reversible Anionic Redox
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Solution Overview
Problem
Current lithium-ion batteries face limitations in achieving high energy densities and cycle life due to the low capacity and structural instability of intercalation cathode chemistries, as well as the poor reversibility of anionic redox reactions, which restrict their potential and efficiency.
Innovation Solution
A rechargeable lithium-ion battery design utilizing a composite cathode with intercalated lithium halide salts, such as lithium bromide and lithium chloride, in combination with a water-in-salt electrolyte, which enables phase separation of lithium salts and stabilizes anionic-redox reactions within the graphite lattice, enhancing capacity and potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If anionic redox reactions are used to increase capacity, then capacity is improved, but reversibility deteriorates due to poor reversibility of anionic redox reactions
Solution Approach 1:
The patent introduces an intercalation host as an intermediary between the anionic redox reaction and the electrolyte. The oxidized anions are stabilized within the intercalation host structure, which prevents direct contact with the electrolyte and eliminates shuttling reactions. This mediator approach allows the system to achieve both high capacity from anionic redox and good reversibility by preventing structural degradation and side reactions.
Solution Approach 2:
The patent changes the physical state and chemical environment of the anionic redox materials by incorporating them into an intercalation host. This parameter change transforms the reaction mechanism from a conversion reaction with poor reversibility to a topotactic intercalation reaction with excellent reversibility, while maintaining high capacity through anionic redox.
2Quantity of substance
If conversion reaction mechanism is used to achieve high capacity, then capacity is improved, but reversibility deteriorates due to large volume change upon charge/discharge
Solution Approach 1:
The intercalation host serves as a mediator that accommodates the volume changes during charge/discharge cycles. Instead of the active material undergoing large volume changes, the intercalation host provides a stable framework that expands and contracts reversibly, maintaining structural integrity while allowing the anionic redox reactions to proceed with high capacity.
Solution Approach 2:
The patent utilizes topotactic phase transitions within the intercalation host during charge/discharge cycles. These phase transitions involve reversible changes in the crystal structure that accommodate ion insertion and extraction without collapsing the overall framework, thereby maintaining structural stability while enabling high capacity through anionic redox.
3Power
If low-potential graphite anode is coupled with high voltage cathode, then electrochemical potential is expanded to 3.0 to 4.0 V range, but cycle life deteriorates due to structural instability upon over-delithiation
Solution Approach 1:
The patent changes the operating potential window and the chemical environment at the cathode by implementing anionic redox reactions in an intercalation host. This parameter change allows the battery to operate at high voltages (3.0 to 4.0 V range) without the cathode material undergoing the structural degradation associated with over-delithiation, thereby extending cycle life while maintaining high power.
4Reliability
If porous carbon is used to confine anions, then reversibility is improved, but self-discharge increases and cycle life decreases due to undesired shuttling reaction
Solution Approach 1:
The intercalation host acts as an intermediary that physically confines the oxidized anions within its layered structure. This confinement prevents the anions from diffusing into the electrolyte and participating in shuttling reactions, thereby eliminating self-discharge while maintaining high reversibility. The intercalation host provides a stable environment that preserves both reversibility and energy efficiency.
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 battery achieves a high capacity of at least 230 mAh/g and an energy density of 460 Wh/kg, with improved cycle life and coulombic efficiency, surpassing the performance of conventional lithium-ion batteries by stabilizing oxidized anions within the graphite lattice and avoiding shuttling reactions.
Implementation Method 1
the limited gravimetric capacity due to the solubility of lithium salts in aqueous electrolytes. However, by using a water-in-salt electrolyte, we can phase separate the lithium salts from the aqueous electrolyte
Implementation Method 2
stabilizing oxidized anions within the graphite lattice and avoiding shuttling reactions
Implementation Method 3
the anionic redox reactions (O/O2−, S/S2−, etc.), on the other hand, promise much higher capacities by following a conversion reaction mechanism
Data Source
AI summary
The disclosure provides rechargeable lithium ion batteries comprising at least one lithium salt-graphite composite electrode. In particular, the disclosure provides a rechargeable “water-in-bisalt” lithium ion battery with a high potential where at least a portion of the lithium salt is phase separated from the aqueous electrolyte, and where the anionic-redox reaction occurs within the graphitic lattice.