Monocrystalline Sodium-Ion Cathode Composition Against Particle Fragmentation
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Solution Overview
Problem
Sodium-ion batteries face challenges with poor cycle performance and low energy density due to factors like surface crystal structure reconstitution, particle agglomeration, and chemical interactions with the electrolyte, leading to stress and instability in cathode materials.
Innovation Solution
A mono-crystalline cathode material with a specific chemical composition (Na1+aNi1-x-y-z-cMnxFeyMzO2) is developed, incorporating doping and surface coating to prevent direct contact with the electrolyte, particularly HF, thereby inhibiting crystal phase transitions and enhancing cycling stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If transition metal oxides are used as cathode materials to achieve high specific capacity, then the energy density is improved, but the cycle performance deteriorates due to surface crystal structure reconstitution and particle agglomeration
Solution Approach 1:
A surface coating layer is applied to the transition metal oxide cathode material particles. This coating acts as an intermediary barrier that prevents direct contact between the material surface and electrolyte, thereby preventing surface crystal structure reconstitution and particle agglomeration during cycling, while allowing ionic and electronic transport to maintain high specific capacity
Solution Approach 2:
A thin film coating is formed on the surface of the cathode material particles. This flexible shell structure accommodates volume changes during sodium ion insertion and extraction, preventing particle fragmentation and maintaining structural integrity over many cycles, thus improving cycle performance while preserving the high capacity of the underlying transition metal oxide
2Speed
If the cathode material is desalted to increase sodium ion diffusion, then the ionic conductivity is improved, but the structural stability deteriorates due to crystal lattice shifts and phase changes
Solution Approach 1:
The cathode material is designed with a core-shell structure where the core region maintains the desalted composition for high ionic conductivity, while the shell region provides structural stability. This segmentation allows different regions to fulfill different functions: the core enables fast sodium ion diffusion while the shell prevents crystal lattice collapse and phase transitions
3Use of energy by moving object
If high voltage operation is implemented to increase energy density, then the capacity is improved, but the chemical stability deteriorates due to electrolyte oxidation and material deoxidation
Solution Approach 1:
The surface coating serves as a protective intermediary that isolates the cathode material from the electrolyte during high voltage operation. This barrier prevents electrolyte oxidation and material deoxidation reactions that would otherwise occur at high potentials, enabling stable high-voltage operation and maintaining both capacity and chemical stability
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 mono-crystalline cathode material exhibits improved structural stability, reduced particle fragmentation, and enhanced cycle performance, particularly at high temperatures and voltages, leading to increased battery lifespan and efficiency.
Implementation Method 1
surface coating or performing body phase doping and surface coating modification at the same time can effectively avoid direct contact between the material and an electrolyte
Implementation Method 2
body phase doping and surface coating modification
Data Source
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AI summary
The present invention relates to a mono-crystalline cathode material for sodium-ion battery and a preparation method and application thereof. The mono-crystalline cathode material for a sodium ion battery contains the chemical formula of Na1+aNi1-x-y-z-cMnxFeyMzNcO2, wherein - 0.40≤a≤0.25, 0.08≤x≤0.5, 0.05≤y≤0.5, 0≤z<0.26, 0<c<0.1, the M and N are both one or a combination of two or more selected from the group consisting of Ti, Zn, Co, Mn, Al, Zr, Y, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Mg, Ta, Nb, V, Sc, Sr, B, F, P or Cu elements. The mono-crystalline cathode material for sodium-ion battery has a specific chemical composition, has a mono crystal morphology, and good structural stability and integrity. Particle fragmentation can not be produced in the cyclic process, and meanwhile, the cyclic stability of the sodium-ion battery can be improved.