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So-called "rocking-chair" rechargeable batteries that use lithium intercalation compounds for the positive and negative electrodes should be safer than batteries that contain free-lithium metal. Such a cell, using the spinel LilVln204 as the positive electrode and carbon as the negative electrode, was optimized as a function of various operating parameters. These cells reversibly insert 0.32 Li atoms per Mn at an average output voltage of 3.7 V, yielding an effective specific energy of 250 mWh/g of electrode materials (3 times that of Ni-Cd). They can sustain high current rates similar to Ni-Cd batteries, and can be discharged to 0 V without any degradation of their operating conditions. By systematically studying the stability of several electrolyte systems, we were able to minimize electrolyte decomposition (by controlling drastically the charge cut-off voltage) so that these cells show a promising cycle life even at 55°C while maintaining 75% of their initial capacity.

We show that the spinel LiMn204, can also be used as the cathode in rechargeable rocking-chair batteries based on lithium intercalation anodes (carbon, either graphite or petroleum coke). At room temperature, such cells show promising cycle life, an average open-circuit voltage of 3.7 V and a specific energy of 250 Wh/kg of electrode materials (cathode+ anode). In addition, we report a novel easily reproducible solution technique for synthesizing Li2Mn204, at low temperatures (< 100~ using LiI as a mild reducing agent. The cycling behavior of rocking-chair cells using this lithiated phase as the starting cathode is presented. Li2Mn204 appears to be a promising practical "air stable" Li-bearing cathode for rockingchair-type rechargeable cells.

The spinel LiMn 2 O 4 , whose electrochemical activity with Li was discovered in the early 1980s, was put forth in the early 1990s as a possible alternative to LiCoO 2 as a positive electrode material for Li-ion batteries. Ten years later, the Li-ion LiMn 2 O 4 /C cells are on the verge of entering the portable electronics and electric/hybrid vehicle market. This paper retraces the key steps of this decade that were necessary to master the intimate physical/electrochemical relationship of LiMn 2 O 4 , and that led to the development of rechargeable Li-ion LiMn 2 O 4 /C technology. During the long development period, the early supremacy of LiMn 2 O 4 as the only alternative to LiCoO 2 diminished with the development of positive electrode materials that present abundance and cost advantages. Despite the uncertainty of the future of the spinel, successfully translating a fundamental success into a commercial one, we stress that the long learning experience will benefit the scientific battery community aiming at rapidly optimizing the electrochemical performance of alternative materials, such as LiFePO 4 .

To improve the high temperature performance of Li1+xMn2O4/normalcarbon rocking‐chair secondary batteries we searched for and identified a new electrolyte composition whose range of stability extends up to 4.9 V vs. Li at room temperature and 4.8 V vs. Li at 55°C for the LixMn2O4 material. The behavior of the LiMn2O4 composite new electrolyte interface at high voltage (4.2 to 5.1 V vs. Li) shows the superposition of two phenomena: (i) an irreversible behavior due to a very slow electrolyte oxidation caused by the large surface area of carbon black (mixed with the LixMn2O4 active material to improve the conductivity) and (ii) two reversible Li deintercalation‐intercalation processes in the LixMn2O4 spinel structure. In order to evaluate the kinetics of the high voltage phenomena, the behavior of the LiMn2O4/normalnew electrolyte interface was investigated as a function of time and temperature. The electrolyte oxidative degradation is a well‐stabilized reaction with nontime evolving kinetics, and with an activation energy close to 8 kcal/mol. The self‐discharge mechanism is a local redox process involving electrolyte oxidation at the electrode surface and reversible intercalation of Li in the LixMn2O4 spinel structure. The effective stability of this new electrolyte against oxidation allows for better performance of our rocking‐chair cells, in terms of cycle‐life and self‐discharge, over a wider temperature range (−20 to 55°C).