Sodium Ion Battery Cathode Firing Process
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Solution Overview
Problem
The positive electrode active material for sodium ion secondary batteries experiences excessive fusion and reaction during firing, leading to reduced specific surface area and decreased charge and discharge capacities, and the formation of non-contributory crystals like maricite-type NaFePO4 when mixed with solid electrolytes.
Innovation Solution
A method involving the firing of an oxide material at 400° C. to 610° C. in a reducing atmosphere to reduce Fe ions and suppress excessive fusion, using a composition represented by Nax(Fe1−aMa)yP2Oz with specific ranges for x, y, and z, and incorporating a sodium ion conductive solid electrolyte like beta alumina or NASICON to prevent unwanted crystal precipitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high temperature firing is used to reduce Fe ions from trivalent to divalent, then battery performance is improved, but glass powder particles excessively fuse resulting in coarse particles and reduced specific surface area
Solution Approach 1:
The invention changes the firing temperature parameter from conventional high temperature (above 610°C) to a lower range (400-610°C), and combines it with atmosphere control (reducing atmosphere) to achieve the desired Fe ion reduction while preventing excessive particle fusion and maintaining high specific surface area
Solution Approach 2:
The invention uses a composite oxide material containing Fe2O3, P2O5, and Na2O in specific proportions, which enables the reduction reaction to proceed effectively at lower temperatures while maintaining material stability and preventing unwanted side reactions
2Reliability
If positive electrode active material is fired at high temperature, then Fe ions are reduced to divalent ions, but the material reacts with solid electrolyte to precipitate maricite-type NaFePO4 crystal that does not contribute to charge and discharge
Solution Approach 1:
The invention changes the firing temperature parameter to a lower range (400-610°C) and controls the atmosphere as reducing, which prevents the formation of maricite-type NaFePO4 crystal while still achieving sufficient reduction of Fe ions to divalent state, thereby maintaining high charge and discharge capacity
Solution Approach 2:
The invention applies preliminary anti-action by controlling the firing conditions (temperature and atmosphere) in advance to prevent the harmful reaction between the positive electrode active material and solid electrolyte, thus avoiding the formation of non-contributory maricite-type crystals before they can form
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
This approach results in a positive electrode material with enhanced charge and discharge capacities by preventing excessive fusion and reaction, maintaining a high specific surface area, and suppressing the formation of non-contributory crystals, thereby improving battery performance.
Implementation Method 1
By firing the oxide material serving as a raw material in the reducing atmosphere of hydrogen or the like, Fe ions in the oxide material can be sufficiently reduced from trivalent ions to divalent ions
Data Source
AI summary
Provided is a method of manufacturing a positive electrode material for an electrical storage device, the positive electrode material for an electrical storage device including a positive electrode active material represented toy the general formula Nax(Fe1−aMa)yP2Oz, where M represents at least one kind of transition metal element selected from the group consisting of Cr, Mn, Co, and Ni, x satisfies 1.2≤x≤2.8, y satisfies 0.95≤y≤1.6, a satisfies 0≤a≤0.9, and z satisfies 7≤z≤8, the method including a step of firing an oxide material serving as a raw material at from 400° C. to 610° C. in a reducing atmosphere.