Cobalt-Doped Sodium Cathode Material for High-Manganese Cycle Life
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Solution Overview
Problem
Conventional sodium secondary batteries using high-manganese-based oxides suffer from low electrical conductivity, capacity retention, and life efficiency due to excessive manganese, which causes phase transitions and surface deterioration, and existing methods to improve these issues are not effective at a commercial level.
Innovation Solution
A positive electrode active material for sodium secondary batteries is developed, comprising a sodium manganese-based oxide with a high manganese content doped with cobalt, where the surface and inside of the oxide particles are uniformly coated with cobalt to enhance electrical conductivity and stability, using a method that integrates water washing and cobalt coating processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high-manganese-based oxide is used as positive electrode active material, then capacity and cost effectiveness are improved, but electrical conductivity and capability rate deteriorate
Solution Approach 1:
The patent creates a composite structure by coating high-manganese oxide particles with a ternary transition metal oxide layer containing cobalt, nickel, and manganese. This composite approach allows the core to provide high capacity while the coating layer provides electrical conductivity, resolving the contradiction between high manganese content and low conductivity.
Solution Approach 2:
The patent applies local quality modification by creating a coating layer with different composition (higher cobalt and nickel content) on the surface of the high-manganese particles. This localized change in material properties improves electrical conductivity at the particle surface without sacrificing the high manganese content in the bulk material.
2Quantity of substance
If high-manganese-based oxide is used as positive electrode active material, then capacity is improved, but cycle life and capability rate deteriorate
Solution Approach 1:
The patent applies beforehand cushioning by pre-coating the high-manganese oxide particles with a stable ternary transition metal oxide layer before battery operation. This coating layer acts as a protective barrier that prevents surface deterioration and phase transitions during cycling, thereby extending cycle life while maintaining high capacity.
Solution Approach 2:
The composite structure with a stable ternary oxide coating on high-manganese core provides both high capacity (from the manganese-rich core) and long cycle life (from the stable coating layer), resolving the contradiction between capacity and durability.
3Object-generated harmful factors
If water washing treatment is applied to remove sodium by-products, then electrochemical performance is improved, but particle surface damage and sodium ion desorption occur
Solution Approach 1:
The patent merges the water washing process with the cobalt coating process into a single integrated operation. By adding cobalt salt solution during water washing, the patent simultaneously removes sodium by-products and deposits cobalt on the particle surface, eliminating the need for separate washing and coating steps while preventing surface damage.
Solution Approach 2:
The patent uses cobalt salt solution as an intermediary that serves dual functions: it replaces water as the washing medium to prevent surface damage, and simultaneously acts as a cobalt source for coating the particles. This intermediary solution resolves the contradiction between removing contaminants and maintaining surface integrity.
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 cobalt doping improves the electrical conductivity and capability rate of the sodium secondary battery, enhancing its cycle life and reducing surface deterioration, while also allowing for a more cost-effective production by using abundant metals like manganese and cobalt.
Implementation Method 1
a surface and an inside of the secondary particles are doped with cobalt (Co)
Implementation Method 2
a method for removing by-products from the surface of a positive electrode active material by a water washing treatment using distilled water, ethanol, or the like is applied
Implementation Method 3
by performing cobalt coating when the sodium high-manganese-based oxide is washed with water, residual sodium by-products are removed and simultaneously the surface and the inside of the oxide particles are doped with a cobalt element
Implementation Method 4
heat treating a product of b) to dope the surface and the inside of the sodium manganese-based oxide particles with cobalt
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 2A~2B
AI summary
Provided are a positive electrode active material for a sodium secondary battery including: a sodium manganese-based oxide which includes at least sodium (Na), nickel (Ni), and manganese (Mn) and contains 55 mol% or more of manganese in all metals other than sodium, wherein the sodium manganese-based oxide is a secondary particle formed by agglomeration of at least one primary particles, and a surface and an inside of the secondary particles are doped with cobalt (Co), a method for producing the positive electrode active material, and a positive electrode and a sodium secondary battery including the positive electrode active material.