Phosphorus-Containing Cathode Mix for Imide Electrolyte Stability
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Solution Overview
Problem
Nonaqueous electrolyte energy storage devices using imide salts at conventional concentrations face issues with increased internal resistance due to aluminum oxidation and corrosion, which degrades charge-discharge performance, and high viscosity at high concentrations compromises high-rate-discharge performance.
Innovation Solution
Incorporating a positive electrode mix with a phosphorus atom, where a peak attributed to P2p appears at 135 eV or less in an X-ray photoelectron spectroscopic spectrum, and using an imide salt at a concentration between 0.5 mol/kg and 2 mol/kg to prevent aluminum oxidation and corrosion, thereby maintaining low internal resistance and viscosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an imide salt is used as an electrolyte salt at a commonly employed concentration of about 1 mol/kg, then the dissociability between cation and anion is improved, but the oxidation and corrosion of aluminum occurs easily when the positive electrode operation potential is 4.0 V
Solution Approach 1:
A coating layer containing phosphorus is introduced as an intermediary between the aluminum current collector and the imide salt electrolyte. This coating layer acts as a protective mediator that prevents direct contact and harmful reactions between the aluminum and imide salt, while still allowing ionic conduction to occur. The phosphorus-containing coating serves as a buffer that eliminates the harmful oxidation and corrosion effects.
Solution Approach 2:
The phosphorus-containing coating is applied in advance to the aluminum current collector before assembling the battery. This preliminary protective action creates a pre-formed barrier that prevents the oxidation and corrosion reactions from occurring during subsequent battery operation. The protective effect is established before any harmful reactions can take place.
2Reliability
If an imide salt is used at a high concentration, then the oxidation and corrosion of aluminum is suppressed, but the viscosity increases and high-rate-discharge performance is compromised
Solution Approach 1:
Instead of uniformly increasing the imide salt concentration throughout the entire electrolyte (which would increase viscosity), the phosphorus-containing coating provides localized protection only at the aluminum current collector surface. This allows the bulk electrolyte to maintain a low concentration of imide salt (0.5-2 mol/kg) for optimal conductivity and low viscosity, while the coating provides targeted corrosion protection where it is most needed.
Solution Approach 2:
The invention changes the protection mechanism from relying on high imide salt concentration to relying on the presence and properties of the phosphorus-containing coating. By adjusting the coating composition and structure rather than the bulk electrolyte concentration, the system achieves corrosion protection without the penalty of increased viscosity.
3Productivity
If an imide salt is used at a concentration not deemed as high concentration, then the viscosity is reduced, but the internal resistance after charge-discharge cycle is greatly increased due to aluminum oxidation and corrosion
Solution Approach 1:
The phosphorus-containing coating serves as a protective intermediary that decouples the relationship between imide salt concentration and internal resistance. By blocking direct contact between the aluminum and imide salt, the coating prevents corrosion-induced resistance increase, allowing the use of low imide salt concentrations without suffering from the penalty of high internal resistance.
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 prevents the increase in internal resistance and maintains high-rate-discharge performance at lower temperatures, even at non-high concentrations of imide salts, enhancing capacity retention and energy density.
Implementation Method 1
the oxidation and corrosion of aluminum that is used as, for example, a positive electrode base material in a nonaqueous electrolyte energy storage device may occur
Implementation Method 2
An imide salt has higher dissociability between a cation and an anion compared with LiPF6 and the like which have been widely used as electrolyte salts
Data Source
Figure 1~2
AI summary
One aspect of the present invention is a nonaqueous electrolyte energy storage device including: a positive electrode including a positive electrode mix containing a phosphorus atom; and a nonaqueous electrolyte containing an imide salt, wherein a peak attributed to P2p appears at a position corresponding to 135 eV or less in an X-ray photoelectron spectroscopic spectrum of the positive electrode mix. Another aspect of the present invention is a method for manufacturing a nonaqueous electrolyte energy storage device including: a positive electrode including a positive electrode mix produced using a positive electrode mix paste containing an oxoacid of phosphorus; and a nonaqueous electrolyte containing an imide salt.