Starting from Mn͑OH͒ 2 and KMnO 4 in LiOH aqueous solution, the nanosized nonstoichiometric Li x MnO 2 with a rhombohedral structure were successfully synthesized via a low-temperature redox soft-chemistry route under the protection of liquid olefin at 353 K. Meanwhile, a partial doping by cations ͑Bi 3+ and Cu 2+ ͒ or polyanions ͑BO 3 3− , PO 4 3− , and SiO 3 2− ͒ in nonstoichiometric Li x MnO 2 was also performed. The microstructure and composition of the samples were characterized by X-ray diffraction, transmission electron microscopy, and inductively coupled plasma atom emission spectroscopy. It is shown that these samples with the rhombohedral structure have irregular shapes with a grain diameter between 20 and 40 nm. The electrochemical performance of these samples as cathode materials was studied by galvanostatic method and electrochemical impedance spectroscopy. The large cation or polyanion doping in nanosized Li x MnO 2 can improve the cycle stability and high-rate discharge capability.Layered lithium-manganese oxides are of interest in the application as cathode materials for lithium-ion batteries because of their low cost, high energy density, and environmental friendship. 1 In these layered lithium-manganese oxides, monoclinic LiMnO 2 ͑space group C2/m, hereafter denoted as m-LiMnO 2 ͒, orthorhombic LiMnO 2 ͑space group Pmmn, hereafter denoted as o-LiMnO 2 ͒, and rhombohedral LiMnO 2 ͑space group R3m, hereafter denoted as r-LiMnO 2 ͒ are electrochemically active materials as stoichiometric LiMnO 2 or nonstoichiometric Li x Mn y O 2 . 2-5 However, it is difficult to inhibit the irreversible structural transformation from the layered lithium-manganese oxides to a spinel structure during electrochemical cycling. It was recently reported that the structural transformation rate of the nonstoichiometric layered Li x Mn y O 2 was significantly slower than that of the stoichiometric layered LiMnO 2 . 6 The layered rhombohedral structure is favorable for lithium insertion and extraction, which is similar to low-temperature LiCoO 2 . 7 Usually, Mn 3+ is a Jahn-Teller active ion in r-LiMnO 2 , resulting in a cooperative monoclinic distortion and instability of the rhombohedral phase. 8 According to the first-principles calculations, the JahnTeller effect in the low-spin state should be absent and the layered structure can be stabilized in r-LiMnO 2 . 9 Cation doping or substituting is in favor of the layered rhombohedral structure against Jahn-Teller distortion, 10,11 which has superior Li-insertion/ extraction cycling properties for r-LiMnO 2 . Besides, polyanions can also be partially introduced into r-LiMnO 2 in place of O 2− ions, where the large polyanions can generate an open three-dimensional ͑3D͒ framework, 12 which enhances fast mobility of Li + ions. In all polyanions, PO 4 3− , BO 3 3− , and SiO 3 2− anions were demonstrated to be valuable constituents in LiMPO 4 , LiMBO 3 , and Li 2 MSiO 4 ͑M = Mn, Fe, Co͒ cathode materials. 13-20 However, a significant drawback is that it is difficult to synthesize...