Large-Agglomerate-Size Lithium Manganese Oxide Spinel with High Rate Capability for Lithium-Ion Batteries

Abstract

Lithium manganese oxide spinel (LiMn 2 O 4 ) is gaining prominence as a positive electrode material for lithium-ion batteries. After an extensive research effort (see, for example, Ref. 1-3), LiMn 2 O 4 spinel with good cycling stability is now available. LiMn 2 O 4 is an attractive alternative to Co and Ni oxides currently used in lithiumion batteries. [4][5][6] For certain applications, such as in electric vehicles, lithium-ion batteries are required to have a high specific power in addition to a high specific energy. 7-10 Thus, electrode materials with high rate capability are of interest.The main strategies adopted so far to reach a high rate capability of the spinel electrode have been the preparation of spinel particles with small sizes, and an optimization of the electrode conductivity. 11-16 However, for industrial battery electrode coating processes, relatively large particles with a small Brunauer-Emmett-Teller (BET) surface area are advantageous. In the present report, we show that it is not necessary to use micrometer-or submicrometer-sized oxide particles when aiming at high rate capabilities. We adapted a high-temperature synthesis route for preparing a spinel consisting of agglomerates with an average size of 15 m. The agglomerates were composed of primary particles (ca. 0.5-3 m). We measured the discharge capability of electrodes containing this spinel up to a discharge rate of 20 C (3 min for full discharge) in an electrochemical test cell with a metallic lithium counter electrode and found a high rate capability for this spinel. ExperimentalSpinel synthesis.-The lithium manganese oxide spinel was synthesized using a proprietary ceramic process. A mixture of manganese oxide (Mn 3 O 4 ) with a specific surface area of about 10 Ϯ 5 m 2 /g and ground lithium carbonate with a particle size of less than about 40 m was heated for 1 h under N 2 to about 750ЊC. The resulting product, which did not yet have a spinel structure, was thoroughly ground. This spinel precursor material was suspended with about 1 wt % of polyvinyl alcohol in water and spray-dried to form a granular powder. This powder was oxidized in O 2 at a temperature of about 780ЊC to form the spinel. The spinel was finally coated with Li 2 CO 3 by spray-drying an aqueous slurry of the spinel and 1 wt % of the coating substance in a stream of hot air (200-300ЊC).Physical characterization.-The lattice constant of the spinel was determined at room temperature by powder X-ray diffraction (XRD) in a Siemens D5000 diffractometer. It was found to be 8.224 Å. The lithium content of the spinel was calculated to be Li 1.09 Mn 1.91 O 4 (by linear interpolation of the lattice constants, 8.248 Å for Li 1.00 Mn 2.00 O 4 and 8.16 Å for Li 1.333 Mn 1.667 O 4 ). 17The particle size distribution of the spinel was determined in an aqueous slurry of the spinel powder by laser scattering using a Helos instrument. The result is shown in Fig. 1. The average particle (agglomerate) size is 15 m.Scanning electron micrographs (SEMs) of the spinel were recorded with a...

Single-Crystalline LiMn2O4 Nanotubes Synthesized Via Template-Engaged Reaction as Cathodes for High-Power Lithium Ion Batteries

“…35-0782), implying that partial manganese sites might be occupied by lithium in the spinel LiMn 2 O 4 lattice. [ 26 ] This is also supported by the ICP-AES results, which shows that the atomic ratio of Li:Mn is 0.54, indicating that a lithium-rich phase of Li 1.05 Mn 1.95 O 4 formed after lithium intercalation during the template-engaged process.…”

Nanostructured LiMn2O4 prepared by a glycine-nitrate process for lithium-ion batteries

“…This rate capability is higher than the rate capability for the spinel LiMn 2 O 4 prepared by a conventional solid-state reaction, as shown in Fig. 5(b), as well as those reported for the spinels fabricated by the similar solid-state reactions [18,19], but smaller than those for the spinels created by sophisticated techniques such as a template method [20] and spray-drying process [21]. Nevertheless, the combustion process has a great potential to create a variety of morphologies with different rate capacities because the rate capability depends critically on the electrochemically active surface area and/or pore size of the powders.…”

Flame co-synthesis of LiMn2O4 and carbon nanocomposites for high power batteries

“…One leading alternative cathode material to LiCoO 2 is LiMn 2 O 4 for its lower cost, higher electrochemical potential vs. graphite, and its improved thermal stability [1][2][3]. High power applications such as electric vehicles require that lithium-ion batteries have a high specific power and energy [4,5].…”