Prelithiation Activates Li(Ni_0.5Mn_0.3Co_0.2)O₂ for High Capacity and Excellent Cycling Stability

Abstract

Transition metal oxide materials Li(NixMnyCoz)O2 (NMC) based on layered structures are expected to replace LiFePO4 in automotive Li-ion batteries because of their higher specific capacity and operating potential. However, the actual usable capacity is much lower than the promised theoretical value [Uchaker, E.; Cao, G. Nano Today 2014, 9, 499-524; Tarascon, J.-M.; Armand, M. Nature 2001, 414, 359-367], in addition to the often poor cycling performance and the first-cycle Coulombic efficiency, for which Mn(II)-dissolution, its immobilization in solid electrolyte interface (SEI), oxidation of electrolytes by Ni, and other parasitic process thereat have been held responsible [Zhan, C., et al. Nat. Commun. 2013, 4, 2437; Wang, L., et al. J. Solid State Electrochem. 2009, 13, 1157-1164; Lin, F., et al. Nat. Commun. 2014, 5, 4529]. Previously, we reported a composite Li(Ni0.5Mn0.3Co0.2)O2 (NMC532) depolarized by the embedded carbon nanotube (CNT) and achieved capacity close to the theoretical limit [Wu, Z., et al. Nano. Lett. 2014, 14, 4700-4706]; unfortunately, this high capacity failed to be maintained in long-term cycling due to the degrading contacts between the active ingredient and CNT network. On the basis of that NMC532/CNT composite, the present work proposes a unique "prelithiation process", which brought the cathode to low potentials before regular cycling and led to an interphase that is normally formed only on anode surfaces. The complete coverage of cathode surface by this ∼40 nm thick interphase effectively prevented Mn(II) dissolution and minimized the side reactions of Ni, Co, and Mn at the NMC interface during the subsequent cycling process. More importantly, such a "prelithiation" process activated a structure containing two Li layers near the surface of NMC532 particles, as verified by XRD and first principle calculation. Hence, a new cathode material of both high capacity with depolarized structure and excellent cycling performance was generated. This new structure can be incorporated in essentially all the NMC-based layered cathode materials, providing us with an effective tool to tailor-design future new cathode materials for lithium batteries.

Pre-Lithiation of Li(Ni1-x-yMnxCoy)O2 Materials Enabling Enhancement of Performance for Li-Ion Battery

“…However, compared with the Ni 3+ free NMC442 material, NMC532 obviously outperforms in the both capacity While the excess capacity released at potential above 3.0 V can be attributed to the Ni 3+ content in NMC materials, the improved cycling stability observed on all the NMC materials should arise from the protective interphase formed during the pre-lithiation process as discussed in our previous work. 7 For the samples prepared by slurry method in this paper, the interphase can also be discovered on both NMC442…”

“…The (001) peak which stands for double layered Li structure can be observed when the discharge voltage is below 1.5 V, 15 as it happened in NMC532 lattice in our previous work. 7 The double layered Li structure serves as a reversible Li source when the battery is charged back to 4.0 V.…”

“…This is in well agreement with the XRD detection of a new peak NMC (001) close to the (003) peak ( Figure 5c). 7,15 Then the average delithiation potentials of the excess Li storage for this prelithiation NMC group were calculated, based on the classic equation: 20…”

Surface modification of LiNi 0.5 Co 0.2 Mn 0.3 O 2 cathode materials with Li 2 O‐B 2 O 3 ‐LiBr for lithium‐ion batteries

“…Compared with LCO, NCM523 has lower toxicity, higher capacity, lower cost, and better safety properties . However, NCM523 suffers low cycle stability and poor high rate performance because of its corrosion by electrolyte …”

Feasibility of Cathode Surface Coating Technology for High‐Energy Lithium‐ion and Beyond‐Lithium‐ion Batteries

“…Hence, research studies have been focused on cathode surface modifications via simple heat-treatments, doping with ions of different elements, and coating with organic/inorganic electrochemically active/inactive materials, resulting in residual-free particle surfaces, bulk crystal structure stability, and better physical protection and improved ionic/electronic conductivity of the particle surface, respectively, after heat-treatment during simple heating, doping, and surface coating procedures. [49][50][51] Therefore, it is essential to introduce hybrid surface treatment approaches to resolve the above problems: an inorganic metal oxide coating and surface doping in which the selected elements are strongly localized to minimize the capacity loss and stabilize the surface and bulk structure of each cathode particle. [38] Nevertheless, the crystal structure instability (layered to spinel phase conversion) of the layered class of cathode materials and the corresponding voltage decay under long-term cycling under the adverse conditions at >4.5 V could not be ruled out.…”