Polyaniline is coated on Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 synthesized via co-precipitation. X-ray diffraction patterns exhibit that the polyaniline coating does not affect structural change of the Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 , and the resulting transmission electron microscopic images show the presence of coating layers on the surface of Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 . Electrochemical tests using coin type cells confirm that the surface modification by polyaniline is effective in maintaining capacity and retention upon cycling. The conducting coating character also assists improvement in rate capability. The polyaniline layer forms F-doped polyaniline during cycling, as is proved by time-of-flight secondary ion mass spectroscopy. Therefore, the presence of the polyaniline layers plays a role in lowering HF levels via scavenging F − from HF in the electrolyte, and this F-doped polyaniline layer also assists in protecting the Li [Li 0.2 Efforts have been made to improve their intrinsic low rate capability stemming from the tetravalent Mn in the oxide matrix and cyclability as well. Hence, partial substitutions of Mn site with other elements or surface modifications have been made. 10,12 A recent report by Kang et al. 14 suggested that surface modification by Al(OH) 3 on Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 was fairly effective in capacity retention, rate capability, and thermal stability. Similar effects were also reported using Al 2 O 3 coating and AlPO 4 coating on the over-lithiated manganese oxides. 17,18 Furthermore, we perceive the main problem of oxide coating to be difficulty in complete encapsulation of active materials like core-shell materials due to condensation and crystal growth of the coating materials even at mild heat-treatment condition; it, hence, shows an islands-like coating. 18 For the reason, we object to complete encapsulation of Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 using a conductive polyaniline, which does not need further heat-treatment after polymerization. Also, the conductive coating layers are expected to improve the rate capability of the active material. In this paper, we introduce the details of polyaniline-coated Li [ • C for 5 h. The dehydrates were thoroughly mixed with an appropriate amount of LiOH (samchun) and calcined at 900 • C for 15 h in air. In attempt to modify the as-synthesized active materials with polyaniline (hereafter referred as to be PANi), Cl − -doped emeraldine salt state PANi ([C 24 H 26 N 4 (Cl) 2 ] n ) was polymerized with aniline monomer (C 6 H 5 NH 2 ) and ammonium persulfate ((NH 4 ) 2 S 2 O 8 ,). First, aniline monomer and ammonium persulfate were separately poured into 1M HCl aqueous solution, and they were mixed to self-polymerize for 2 days. And the produced PANi in the solution was rinsed with absolute ethanol and acetone to remove the residual monomer, oligomer, and low molecular weight organic intermediates. To prepare violet pernigraniline base state (hereafter referred as to be VPB) PANi which needs to be dissolved in N-methyl-2-pyrrolinon(NMP) or m-cresol and so on, 19,20 the Cl − -doped PANi was poured into a 1M NaOH aqueous solution and continuously stirred at 350 rpm for 2 days. Then, the solution was dried at 80 • C in air. The obtained VPB powders were mixed with campor-10-sulfonic acid, β (CSA, Sigma-aldrich, with a ratio of 4:1 in weight) to prepare (SO) 3 2− -doped emeraldine salt state (hereafter referred as to be ES) PANi and dissolved into N-methyl-2-pyrrolinon (NMP X-ray diffractometry (XRD, Rint-2000, Rigaku) and highresolution transmission electron microscopy (HR-TEM, JEM-3010, JEOL) were employed to characterize the synthesized powders. Timeof-flight secondary ion mass spectroscopy (ToF-SIMS, PHI TRIFT V nanoTOF, ULVAC-PHI) was also used to confirm the presence of th
