Composite-material cathodes that enable Li-ion electrochemical cells and batteries to function at both high energy densities and high discharge rates are undergoing development. Until now, using commercially available cathode materials, it has been possible to construct cells that have either capability for high-rate discharge or capability to store energy at average or high density, but not both capabilities. However, both capabilities are needed in robotic, standby-power, and other applications that involve duty cycles that include long-duration, low-power portions and short-duration, high-power portions.
The electrochemically active ingredients of the present developmental composite cathode materials are the following:
- Carbon-coated LiFePO4, which has a specific charge capacity of about 160 mA·h/g and has been used heretofore as a high-discharge-rate cathode material; and
- Li[Li0.17Mn0.58Ni0.25]O2, which has a specific charge capacity of about 240 mA·h/g and has been used heretofore as a high-energy-density cathode material.
In preparation for fabricating a composite-material cathode in the approach followed thus far in this development effort, the aforementioned electrochemically active ingredients are incorporated into two sub-composites:
- A mixture comprising 10 weight percent of poly(vinylidene fluoride) [PVDF], 10 weight percent of carbon, and 80 weight percent of carbon-coated LiFePO4 and,
- A mixture comprising 10 weight percent of PVDF, 10 weight percent of carbon, and 80 weight percent of Li[Li0.17Mn0.58Ni0.25]O2.
In the fabrication process, these mixtures are spray-deposited onto an aluminum current collector. While the two mixtures could be spray-deposited simultaneously on the same current-collector area to obtain a single layer comprising a mixture of two sub-composites, electro-chemical tests performed thus far have shown that better charge/discharge performance is obtained when either (1) each mixture is sprayed on a separate area of the current collector or (2) the mixtures are deposited sequentially (in contradistinction to simultaneously) on the same current-collector area so that the resulting composite cathode material consists of two different sub-composite layers.
This work was done by Jay Whitacre, William West, and Ratnakumar Bugga of Caltech for NASA's Jet Propulsion Laboratory.
NPO-44837
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Composite Cathodes for Dual-Rate Li- Ion Batteries
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Overview
The document discusses advancements in battery technology, specifically focusing on dual-rate composite lithium-ion (Li-ion) battery cathodes developed by NASA's Jet Propulsion Laboratory (JPL). The primary challenge addressed is the limitation of current battery cathode materials, which either provide high rates with low or average capacity or high capacity with limited rate performance. This creates a need for a battery system that can effectively support both high power demands and high energy storage.
To solve this problem, the researchers have created a novel cathode structure that combines two different materials: LiFePO4, known for its high power density, and Li[LiMnNi]O2, which offers high energy density. The specific capacities of these materials are 160 mAh/g for LiFePO4 and 240 mAh/g for Li[LiMnNi]O2. By mixing these materials in various configurations, the researchers have developed a bi-polar design that allows both materials to contribute effectively to the battery's performance during variable rate discharge cycles.
The innovation lies in the ability of this composite cathode to deliver both high specific energy at low discharge rates and the capability to support intermittent high-rate discharges, which are often required in hybrid power systems. This dual functionality makes the composite battery superior under certain conditions compared to batteries made from either of the pure materials alone.
The document emphasizes the potential applications of this technology beyond aerospace, suggesting that the advancements in composite cathodes could have significant implications for various technological, scientific, and commercial fields. The research is part of NASA's Commercial Technology Program, aimed at making aerospace-related developments accessible for broader use.
For further inquiries or detailed information, the document provides contact details for the Innovative Technology Assets Management at JPL, encouraging collaboration and exploration of these advancements in battery technology. Overall, the development of dual-rate composite Li-ion batteries represents a significant step forward in energy storage solutions, particularly for applications requiring both high power and high energy efficiency.
