Layered Li[sub 1+x](Ni[sub 0.425]Mn[sub 0.425]Co[sub 0.15])[sub 1−x]O[sub 2] Positive Electrode Materials for Lithium-Ion Batteries

Abstract

Layered Li 1+x (Ni 0.425 Mn 0.425 Co 0.15 ) 1-x O 2 materials (0 x 0.12) were prepared at 1000°C for 12 h in air by a coprecipitation method. As x increased in Li 1+x (Ni 0.425 Mn 0.425 Co 0.15 ) 1-x O 2 , the substitution of x Li + ions for x transition metal ions induced for charge compensation an increase in the average transition metal oxidation state. X-ray photoelectron spectroscopy analyses showed that cobalt and manganese were present in these materials in the trivalent and tetravalent states, respectively, and that increasing overlithiation led to the oxidation of Ni 2+ ions into Ni 3+ ions. The refinement of the crystal structure of these materials in the R m space group and magnetic measurements showed a decrease in the Ni occupancy in the Li layers with increasing overlithiation. From an electrochemical point of view, the reversible capacity in the 2-4.3 V range decreased with overlithiation Keywords :Although LiCoO 2 is suitable for the lithium-ion battery application, its high cost and toxicity prevent its use in low-price or large devices. Positive electrodes with LiNiO 2 revealed an attractive reversible capacity 1 but suffered from a quite poor capacity retention 2 and also from a low thermal stability of their deintercalated phases. 3,4,5,6 Partial substitution for nickel allowed an optimization of these properties for compositions such as LiNi (1-x-y) Co x Al y O 2 . 7,8,9 Nevertheless, there is still a need for cheaper and safer positive electrode materials with higher electrochemical performances. Recently lithium-rich manganese-based materials such as Li[Ni x Li (1/3-2x/3) Mn (2/3-x/3) ]O 2 and Li[Co x Li (1/3x/3) Mn (2/3-2x/3) ]O 2 were extensively studied by various research groups. 10,11,12,13 Interesting results were obtained, for instance for the Li[Ni 1/3 Li 1/9 Mn 5/9 ]O 2 phase with a capacity of 230 mAh/g between 2.0 and 4.6 V at 55°C. 14 In all these materials, the manganese ions are in the tetravalent state in the pristine material 15 so that they are electrochemically inactive. Because there are no Mn 3+ ions, no structural evolution to the spinel structure is expected to occur upon cycling, on the contrary to what was observed for the layered LiMnO 2 . 16,17,18,19 Furthermore, the presence of a large amount of manganese ions at the stable tetravalent oxidation state is thought to be responsible for a higher thermal stability. Differential scanning calorimetry experiments (DSC) on charged electrodes of Li[Ni x Li (1/3-2x/3) Mn (2/3-x/3) ]O 2 for x=5/12 indicate that this material should be thermally safer than LiCoO 2 . 10 The DSC profiles of the fully oxidized Li x [Li 0.12 Ni z Mg 0.32-z Mn 0.56 ]O 2 (z=0.3) material also demonstrate much higher thermal stability than Li x CoO 2 . 20 Note also that most of these overlithiated materials exhibit an irreversible plateau at around 4.5 V/Li during the first charge. The origin of this plateau was attributed by Lu and Dahn to be due to an irreversible oxygen loss. 14

Online Electrochemical Mass Spectrometry of High Energy Lithium Nickel Cobalt Manganese Oxide/Graphite Half- and Full-Cells with Ethylene Carbonate and Fluoroethylene Carbonate Based Electrolytes

“…This is not the case in the SFG6/Li half-cells, where the SFG6 electrode is positioned at the top, in close proximity to the gas head-space. Analogously, the oxidative CO 2 and O 2 peaks are not broadened in the full-cells, because the corresponding formation processes take place at the HE-NCM electrode, which is located at the top in both HE-NCM/Li half-and full-cells. In fact, upon interchanging the positions of the HE-NCM and SFG6 electrodes in the full-cells, the evolution traces of the gases formed at or close to the HE-NCM electrode, are affected considerably (Figure 2, Figure S1, Figure S2).…”

“…LiCoO 2 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 , etc.) due to its high specific charge (≈250 mAh g −1 ) and operation potential (up to 4.7 V vs. Li + /Li).…”

The Role of Oxygen Release from Li- and Mn-Rich Layered Oxides during the First Cycles Investigated by On-Line Electrochemical Mass Spectrometry

“…11,13,14 The two structures are very close to each other despite this difference in symmetry, related simply to the Li + ordering in the transition metal sites. This similarity is evident in the structure of the Li-rich NCM Li 1+x Me 1-x O 2 (Me = Ni, Co, Mn), also referred to as high-energy NCM (HE-NCM), where the hexagonal symmetry of the layered structure is broken by the superstructure of Li + in the transition metal sites, shown by the superlattice reflections in the diffractograms.…”

“…10,11 These so-called Lirich compounds result from the substitution of part of the transition metal ions by Li + , in a structural arrangement closely related to the layered structure. [11][12][13][14] Li 2 MnO 3 (or Li[Li 1/3 Mn 2/3 ]O 2 ) is the simplest structure in this category and crystallizes in the monoclinic system (space group C2/m), while the common LiMeO 2 -based layered structures crystallize in the hexagonal system (space group R-3m). 11,13,14 The two structures are very close to each other despite this difference in symmetry, related simply to the Li + ordering in the transition metal sites.…”

Direct evidence of oxygen evolution from Li1+x (Ni1/3Mn1/3Co1/3)1−x O2 at high potentials

“…NMC compounds show higher thermal stability [2][3][4], good cycling stability, and higher specific charge with respect to LiCoO 2 [5] (ca. 150 mAh g -1 for the NMC compound with x = 0 when cycling in the potential window from 2.5 to 4.4 V vs. Li/Li + ).…”