Composite Sodium-Ion Anodes for Higher Volumetric Capacity
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Solution Overview
Problem
The limited volumetric energy density of sodium-ion batteries compared to lithium-ion batteries hinders their widespread adoption, with typical Na-ion battery negative electrodes like hard carbon having a capacity of less than about 450 mAh/cm3.
Innovation Solution
A composite anode active material comprising a carbon active material and an alloying element such as phosphorus, tin, lead, or combinations thereof, with a binder and conductive additive, is used to enhance the energy storage performance of sodium-ion batteries, allowing for improved capacity retention and volume expansion during cycling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If typical hard carbon negative electrodes are used in Na-ion batteries, then the device structure is simple and easy to manufacture, but the volumetric energy density is limited to less than about 450 mAh/cm3
Solution Approach 1:
The patent applies composite materials by combining hard carbon with alloying elements (Sn, Pb, P, Sb, Bi, or Ge) to create a composite anode active material. This composite structure enables the material to achieve volumetric energy density of at least 450 mAh/cm3 while maintaining manufacturability, as the composite can be processed using conventional electrode fabrication techniques.
2Quantity of substance
If alloying elements are added to improve capacity, then the specific capacity increases to at least 370 mAh/g, but the electrode experiences significant volume expansion during cycling
Solution Approach 1:
The patent applies parameter changes by controlling the particle size of alloying elements to be 150 μm or less, and optimizing the weight ratio of alloying element to hard carbon (5-95 wt%). These parameter optimizations enable the electrode to achieve high specific capacity (≥370 mAh/g after 100 cycles) while managing volume expansion through appropriate material selection and size control.
Solution Approach 2:
The patent applies beforehand cushioning by pre-mixing alloying elements with hard carbon particles before electrode fabrication. This pre-composite structure provides a cushioning effect where the hard carbon matrix accommodates the volume expansion of alloying elements during sodiation, preventing electrode degradation while maintaining high capacity.
3Quantity of substance
If the anode film thickness is increased to improve capacity, then the energy storage increases, but the first cycle efficiency decreases to below 85%
Solution Approach 1:
The patent applies local quality by creating a composite structure where alloying elements are distributed throughout the hard carbon matrix at the particle level. This local distribution ensures uniform electrochemical reactions throughout the electrode thickness, maintaining first cycle efficiency of at least 85% even in thicker films, as each local region contributes effectively to capacity.
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 composite anode active material achieves a specific capacity of at least 370 mAh/g after 100 cycles, with a first cycle efficiency of 85% and coulombic efficiency of 99% after 20 cycles, and capacity retention of 90% after 200 cycles, while accommodating significant volume changes without impedance growth or active mass loss.
Implementation Method 1
Alloying anode active materials for sodium-ion energy storage devices, and methods thereof
Data Source
AI summary
An anode active material for a sodium ion energy storage device with improved volumetric capacity, capacity retention, and coulombic efficiency and the method thereof is disclosed. The anode active material comprises an alloying element. The anode active material may further comprise a carbon active material. The alloying element may be selected from phosphorus (P), germanium (Ge), tin (Sn), antimony (Sb), lead (Pb), and bismuth (Bi). The anode comprising the anode active material shows improved capacity retention.