Prelithiated Li-Si Negative Electrodes With Thiophosphate Shells
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Solution Overview
Problem
Secondary lithium batteries face issues with irreversible capacity loss and reduced cycle life due to the formation of a solid electrolyte interphase (SEI) on silicon-based negative electrodes, which consumes active lithium and is destabilized by volume changes during charging and discharging.
Innovation Solution
A lithium-silicon alloy core is encapsulated with a lithium thiophosphate solid electrolyte layer, forming a core-shell structure that prevents undesirable reactions and maintains ionic conductivity, allowing for a stoichiometric surplus of lithium and improved oxidative and humidity resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode material is used to increase specific capacity, then the amount of active lithium available increases, but irreversible capacity loss occurs due to SEI formation consuming active lithium
Solution Approach 1:
The patent applies preliminary action by pre-forming a stable solid electrolyte interphase (SEI) layer on the silicon-based negative electrode material before the battery enters service. This initial SEI formation consumes excess lithium in a controlled manner during a preliminary conditioning cycle, so that the protective layer is already in place before normal operation begins. As a result, during subsequent cycling, the pre-formed SEI prevents further parasitic lithium consumption, thereby increasing the amount of active lithium available for productive cycles while minimizing irreversible capacity loss.
2Quantity of substance
If silicon-based negative electrode material is used to increase specific capacity, then more lithium can be stored, but the SEI layer is destabilized by volume changes during charging and discharging
Solution Approach 1:
The patent applies parameter changes by modifying the composition and structure of the SEI layer through controlled preliminary electrochemical cycling. During this conditioning process, parameters such as electrolyte composition, cycling rate, and voltage windows are optimized to form an SEI layer with enhanced mechanical stability and adhesion. This modified SEI layer can accommodate the volume expansion and contraction of silicon during charging and discharging without destabilizing, thereby maintaining its protective function while allowing the high specific capacity of silicon to be utilized.
3Quantity of substance
If excess lithium is added to compensate for SEI formation, then active lithium availability increases, but battery mass increases reducing energy density
Solution Approach 1:
The patent applies preliminary action by incorporating a controlled amount of excess lithium into the negative electrode structure during manufacturing, specifically designed to be consumed during an initial conditioning cycle. This preliminary lithium consumption forms a stable SEI layer that prevents future parasitic reactions. The amount of excess lithium is precisely calculated to be sufficient for SEI formation but minimal enough to avoid significant mass increase, thereby compensating for lithium loss while maintaining acceptable energy density.
Solution Approach 2:
The patent applies local quality by concentrating the excess lithium specifically in regions where SEI formation is most likely to occur, such as on the surface of silicon particles and at interfaces with the electrolyte. Rather than uniformly distributing excess lithium throughout the entire electrode, the formulation targets specific locations where protective layer formation is needed. This localized approach ensures adequate lithium availability for SEI formation without unnecessarily increasing overall battery mass.
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 core-shell structure stabilizes the negative electrode, reduces lithium consumption, and enhances the electrochemical performance and cycle life of the battery by preventing SEI formation and maintaining ionic conductivity.
Implementation Method 1
Silicon (Si) is a promising electrochemically active negative electrode material for secondary lithium batteries due to its low electrochemical potential (about 0.06 V vs. Li/Li+) and its high theoretical specific capacity (up to about 4200 mAh/g)
Implementation Method 2
an ionically conductive electrolyte that provides a medium for the conduction of lithium ions through the electrochemical cell between the negative and positive electrodes
Implementation Method 3
an electrically insulating and ionically conductive layer referred to as a solid electrolyte interphase (SEI) may inherently form in-situ on a surface of the negative electrode at an interface between the negative electrode and the electrolyte
Data Source
AI summary
A method of making a negative electrode for an electrochemical cell of a secondary lithium battery. The negative electrode includes composite Li—Si alloy particles dispersed in a polymer binder. The composite Li—Si alloy particles are formed by contacting Li—Si alloy particles with a precursor solution that includes a phosphorus sulfide compound dissolved in an organic solvent to form a lithium thiophosphate solid electrolyte layer over an entire outer surface of each of the Li—Si alloy particles.