Silicon Clathrate II Negative Electrode for Li-Ion Batteries
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Solution Overview
Problem
Silicon clathrate II maintains structure after Na separation, making it suitable for use as a negative electrode active material in lithium ion secondary batteries, but existing methods face challenges in inhibiting expansion during charging and discharging, which degrades the electrode.
Innovation Solution
A negative electrode active material containing silicon clathrate II with a specific composition (NaxSi136, 0≤x≤10) and controlled pore volume (≥0.025 cm3/g for pores ≤100 nm) is developed, using a Na getter agent to reduce Na partial pressure and produce silicon clathrate II at lower temperatures, preventing expansion and degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon clathrate II is used as negative electrode active material, then battery capacity is improved, but electrode expansion occurs during charging and discharging
Solution Approach 1:
The patent utilizes silicon clathrate II's inherent porous cage structure with composition formula NaxSi136 (0≤x≤24), where polyhedral cages formed by Si atoms create internal voids. These pores accommodate volume changes during Li ion insertion/extraction, preventing electrode expansion while maintaining structural integrity and enabling high battery capacity.
Solution Approach 2:
The patent employs silicon clathrate II as a composite material combining Si framework with enclosed metal atoms (Na, Li, K, Rb, Cs, or Ba). This composite structure provides both high capacity through alloying reactions and structural stability through the rigid Si cage framework that maintains morphology during electrochemical cycling.
2Loss of substance
If high heating temperature is used to produce silicon clathrate, then Na separation is achieved, but silicon clathrate I structure changes to typical Si crystal
Solution Approach 1:
The patent optimizes heating temperature parameters to range between 200-400°C for producing silicon clathrate II, which is lower than conventional methods. This parameter control achieves sufficient Na separation while preserving the silicon clathrate II structure, avoiding transformation to typical Si crystal that occurs at higher temperatures.
Solution Approach 2:
The patent introduces a Na getter agent as an intermediary substance that facilitates Na removal from the silicon clathrate structure. The getter agent selectively captures Na atoms during heating, enabling Na separation at lower temperatures without requiring excessive thermal energy that would degrade the silicon clathrate framework.
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 solution effectively inhibits expansion of the negative electrode during charging and discharging, enhancing the lifespan of lithium ion secondary batteries by maintaining the structural integrity of the silicon material.
Implementation Method 1
using a Na getter agent to reduce Na partial pressure and produce silicon clathrate II at lower temperatures
Implementation Method 2
The silicon clathrate II maintains the structure even in a case where the contained Na has separated... Expansion of the negative electrode active material of the present invention is inhibited during charging
Data Source
AI summary
Provided is a negative electrode active material that contains silicon clathrate II and that is suitable for a negative electrode of a lithium ion secondary battery. The negative electrode active material includes a silicon material in which silicon clathrate II represented by composition formula NaxSi136 (0≤x≤10) is contained and a volume of a pore having a diameter of not greater than 100 nm is not less than 0.025 cm3/g.