Lithium Titanate Capacitor DCIR Reduction
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Solution Overview
Problem
Conventional electrochemical capacitors experience high direct current internal resistance (DCIR), leading to energy loss and reduced storage efficiency, especially during high-current energy regeneration in applications like automobiles and construction equipment, and this issue is exacerbated by high temperatures, which also shorten the capacitor's lifespan.
Innovation Solution
The electrochemical capacitor design features a positive electrode with activated carbon and a negative electrode with lithium titanate, where the 100% discharge capacity of lithium titanate is set between 2.2 to 7.0 times that of activated carbon, optimizing the utilization ratio of lithium titanate to reduce DCIR and inhibit its increase even at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If lithium titanate is used as negative electrode active material to reduce DCIR, then energy loss is reduced, but solid electrolyte interface film formation increases reactivity and reduces efficiency
Solution Approach 1:
The patent controls the capacity ratio parameter between negative and positive electrodes within 0.95-1.05, and limits operating voltage to 1.5-2.7V, thereby controlling the reactivity of lithium titanate and minimizing SEI film formation while reducing energy loss
2Reliability
If capacity ratio of negative electrode to positive electrode is set within 1.05 to 1.3 to prevent electrolyte decomposition, then cycling stability is improved, but energy density is reduced
Solution Approach 1:
The patent optimizes the capacity ratio parameter to a narrower range of 0.95-1.05 (improved from 1.05-1.3 in prior art), and sets operating voltage range to 1.5-2.7V, achieving both cycling stability and higher energy density by more efficient utilization of electrode materials
3Power
If rapid charging/discharging is implemented in lithium ion secondary battery to improve power output, then charge-discharge cycle reliability deteriorates
Solution Approach 1:
The patent adopts the proven stable structure of electric double layer capacitors (activated carbon electrodes, electrolyte composition, cell architecture) and incorporates lithium titanate's rapid ion transport capability, creating a hybrid device that copies the reliability of capacitors while achieving the power characteristics of high-rate lithium ion batteries
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 configuration results in a capacitor with low DCIR and stable performance, even under high-temperature conditions, by minimizing the reactivity of lithium titanate and reducing the formation of a solid electrolyte interface film, thereby maintaining efficiency and extending the capacitor's lifespan.
Implementation Method 1
a material which can occlude and release a lithium ion is used as a positive electrode active material and a negative electrode active material, a lithium ion is released from the positive electrode and occluded into the negative electrode by charge, and a lithium ion is released from the negative electrode and occluded into the positive electrode by discharge
Implementation Method 2
charging and discharging take place by desorption/adsorption of a cation and an anion in an electrolytic solution from/onto the activated carbon
Implementation Method 3
a solid electrolyte interface (SEI) film is less likely to be formed on the surface of lithium titanate
Data Source
AI summary
Provided is an electrochemical capacitor which has low DC internal resistance, and which minimizes increase in the DC internal resistance due to a high temperature experience. The electrochemical capacitor is provided with a positive electrode having a positive electrode active material layer containing activated carbon, a negative electrode having a negative electrode active material layer containing a spinel-type lithium titanate, and a separator holding a non-aqueous electrolytic solution containing a lithium salt between the positive electrode active material layer and the negative electrode active material layer, a 100% discharge capacity of lithium titanate being set to within a range of 2.2 to 7.0 times a 100% discharge capacity of activated carbon. During charging and discharging of the electrochemical capacitor, only the area near the surfaces of lithium titanate particles are utilized, lowering the DCIR and improving the stability of the DCIR.