Negative Electrode Active Material for Sodium-Ion Batteries
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Solution Overview
Problem
Power storage devices using NaTi2(PO4)3 or Na3Ti2(PO4)3 as negative electrode active materials face issues with high operating voltage and insufficient cycle characteristics, while KNb3O8 has low cycle characteristics and high operating voltage, necessitating a material with low operating potential and improved cycle performance.
Innovation Solution
A negative electrode active material composed of Si, B, P, Al, Nb, and O, with specific mole percentages of Nb2O5, SiO2, B2O3, and P2O5, and the inclusion of R2O and R′O to enhance alkali-ion conductivity and reduce volume change during charge/discharge cycles, incorporating an amorphous phase for improved ion diffusivity and interfacial conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If NaTi2(PO4)3 or Na3Ti2(PO4)3 is used as negative electrode active material, then cycle characteristics are improved, but operating voltage becomes high
Solution Approach 1:
The patent uses a composite material consisting of Nb2O5 combined with SiO2, B2O3, P2O5, and Al2O3 in specific proportions. This composite structure integrates the high cycle stability of Nb-based materials with the low operating voltage characteristics of oxide glass components, achieving both improved reliability and reduced operating voltage compared to pure NaTi2(PO4)3 or Na3Ti2(PO4)3
Solution Approach 2:
The patent optimizes the compositional parameters by controlling the mole ratios of Nb2O5 (5-90%), SiO2+B2O3+P2O5+Al2O3 (5-85%), and R2O+R′O (1-70%). By adjusting these parameters, the material achieves a balance between cycle characteristics and operating voltage, transforming the Ti4+/Ti3+ reaction at 2.2V into a Nb-based redox system with lower potential
2Use of energy by moving object
If KNb3O8 is used as negative electrode active material, then operating voltage is reduced, but cycle characteristics become insufficient
Solution Approach 1:
The patent creates a composite where Nb2O5 is combined with stable oxide glass formers (SiO2, B2O3, P2O5, Al2O3) and alkali/alkaline earth oxides. This composite structure provides the low operating voltage of KNb3O8 while the glass matrix and alkali oxides contribute to improved cycle stability by reducing volume change and maintaining structural integrity during repeated charge-discharge cycles
Solution Approach 2:
The patent introduces local structural modifications through the oxide glass components that surround and stabilize the Nb-based active material regions. The glass matrix provides a flexible local environment that accommodates volume changes during ion insertion/extraction, protecting the NbO2/NbO3 regions from structural collapse while maintaining their low-voltage electrochemical activity
3Quantity of substance
If Si or Sn is used as negative electrode active material, then theoretical capacity is increased, but volume change becomes large causing collapse
Solution Approach 1:
The oxide glass matrix (SiO2-B2O3-P2O5-Al2O3 system) acts as a flexible shell surrounding the Nb2O5 active material particles. This glass matrix can elastically deform to accommodate the volume changes occurring during alkali ion insertion and extraction, preventing the structural collapse that plagues rigid Si or Sn materials while maintaining high theoretical capacity through the Nb-based redox reactions
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 proposed material achieves a low operating potential, increased operating voltage, and excellent cycle characteristics, facilitating higher discharge capacity and voltage retention in power storage devices, particularly suitable for sodium-ion secondary batteries.
Implementation Method 1
a negative electrode active material for a power storage device, which inserts and extracts alkali ions during charge and discharge
Implementation Method 2
since the negative electrode active material contains R2O or R′O, the alkali-ion conductivity can be increased. When the alkali-ion conductivity increases, insertion and extraction of alkali ions during charge and discharge are facilitated
Implementation Method 3
the diffusion coefficient of alkali ions can be increased by previously inserting alkali ions or alkaline earth metal ions into the negative electrode active material
Data Source
AI summary
Provided is a negative electrode active material for a power storage device that has a low operating potential, can increase the operating voltage of the power storage device, and has excellent cycle characteristics. The negative electrode active material for a power storage device, the negative electrode active material containing as elements at least one selected from Si, B, and P; Nb; and O.