Sodium Ion Cell Formation Method for First Cycle Loss
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Solution Overview
Problem
Sodium ion batteries face challenges in optimizing energy density due to high first cycle loss and irreversible sodium loss, particularly when using hard carbon anodes, which affects long-term cycling performance.
Innovation Solution
A method for forming a sodium ion cell using a layered sodium layered oxide cathode material with a disordered carbon anode, where the cell is initially charged to a higher voltage during the formation phase to balance sodium loss on the cathode and anode, allowing for subsequent cycling at a lower voltage to maximize reversible capacity and reduce capacity fade.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the cell is charged to a higher voltage during formation phase, then the first cycle loss is balanced and energy density is improved, but the risk of cathode material degradation and safety issues increases
Solution Approach 1:
The patent applies preliminary action by performing a formation charge at an elevated voltage (4.2V-4.3V) before normal operation. This preliminary high-voltage charge creates an optimized SEI layer and balances sodium distribution, preparing the cell for subsequent stable cycling at lower voltages, thus preventing future performance degradation.
Solution Approach 2:
The patent implements dynamics by using different voltage regimes at different stages of cell operation. The formation phase uses a higher voltage (4.2V-4.3V) to optimize initial conditions, while normal operation uses a lower voltage (4.0V-4.1V) to maintain stability. This dynamic voltage adjustment resolves the contradiction between achieving low first cycle loss and maintaining long-term reliability.
2Reliability
If excess cathode material is used to compensate for first cycle loss, then capacity balance is improved, but the energy density and cost-effectiveness deteriorates
Solution Approach 1:
The patent applies parameter changes by modifying the voltage parameter during formation charge (using 4.2V-4.3V instead of the normal 4.0V-4.1V). This parameter change during the formation phase optimizes sodium distribution and SEI formation, achieving capacity balance without requiring excess cathode material, thus maintaining energy density and cost-effectiveness.
3Reliability
If the cell is capacity limited by the negative electrode during formation, then metal plating is prevented, but the applicability to standard cell formats is reduced
Solution Approach 1:
The patent applies inversion by reversing the traditional capacity limitation approach. Instead of limiting capacity based on the negative electrode (anode), the patent uses a fixed voltage cutoff (4.2V-4.3V) during formation charge. This inverted approach prevents metal plating through voltage control rather than capacity control, making the method universally applicable to all standard cell formats regardless of their specific anode-cathode capacity ratios.
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 effectively balances the first cycle losses on both electrodes, enhancing the longevity and energy density of sodium ion cells by reducing the fade rate and extending cycle life beyond 700 cycles to 80% of initial capacity without the need for excess cathode material or degassing.
Implementation Method 1
Lithium ion cells are a type of rechargeable cell in which lithium ions move from the negative electrode (anode) to the positive electrode (cathode) during discharge and back again when charging. During the charge or discharge, when the lithium ions are moving through the cell, a charge balancing current passes through an external circuit providing power.
Implementation Method 2
for sodium ion technology the intercalation of the larger sodium ions into graphite is problematic
Implementation Method 3
On the anode side of the cell a layer known as the solid electrolyte interphase (SEI) is created. This SEI is formed at the negative electrode because some of the electrolyte components are not stable at the low voltages of this electrode during charging. The product of this decomposition forms a solid layer on the surface of the anode material.
Data Source
AI summary
A method of operating a rechargeable sodium ion cell, wherein the cell comprises an anode material which is a disordered carbon and a nickel-containing sodium oxide cathode material comprises: in a formation charge phase, charging the cell to a first voltage at which sodium is irreversibly liberated from the cathode material; and in a subsequent charge-discharge cycle, charging the cell to a second voltage lower than the first voltage. The voltage to which the cell is charged in the formation charge phase may be selected such that the amount of sodium irreversibly liberated from the cathode material in the formation charge phase substantially equals the amount of sodium deposited in a surface electrolyte layer on the anode in the formation charge phase.