Mitigating Voltage Fade in Cathode Materials by Improving the Atomic Level Uniformity of Elemental Distribution

Abstract

Lithium- and manganese-rich (LMR) layered-structure materials are very promising cathodes for high energy density lithium-ion batteries. However, their voltage fading mechanism and its relationships with fundamental structural changes are far from being well understood. Here we report for the first time the mitigation of voltage and energy fade of LMR cathodes by improving the atomic level spatial uniformity of the chemical species. The results reveal that LMR cathodes (Li[Li0.2Ni0.2M0.6]O2) prepared by coprecipitation and sol-gel methods, which are dominated by a LiMO2 type R3̅m structure, show significant nonuniform Ni distribution at particle surfaces. In contrast, the LMR cathode prepared by a hydrothermal assisted method is dominated by a Li2MO3 type C2/m structure with minimal Ni-rich surfaces. The samples with uniform atomic level spatial distribution demonstrate much better capacity retention and much smaller voltage fade as compared to those with significant nonuniform Ni distribution. The fundamental findings on the direct correlation between the atomic level spatial distribution of the chemical species and the functional stability of the materials may also guide the design of other energy storage materials with enhanced stabilities.

Surface Structure, Morphology, and Stability of Li(Ni1/3Mn1/3Co1/3)O2 Cathode Material

“…Although, during cycling kinetic barriers impede changes in the particle shape. 3 as Li source, and CsCl as the flux (R = 4). The crystals were obtained after heating in air at 900°C for 12 h and then cooling to room temperature at 4°C/min.…”

High‐Performance Heterostructured Cathodes for Lithium‐Ion Batteries with a Ni‐Rich Layered Oxide Core and a Li‐Rich Layered Oxide Shell

“…Additionally, the 20LNM‐ALF 3 ‐coated LNCM sample shows superior specific energy and average working voltage retentions (Figure 4b,c). Considering that the serious drawback of the Mn‐based Li‐rich materials is the working voltage decline, the heterostructure presented here offers the advantage of not only minimizing the shortcomings of the poor energy retention of the Li‐rich oxide but also maximizing the strong points in terms of high capacity and stability 5, 15…”

“…To overcome this problem, many studies have focused on stabilizing the structure with various efforts, such as surface modifications and transition‐metal‐ion substitutions,2, 5, 6, 7, 8 but none of the efforts could completely eliminate the phase transition. In this regard, new approaches are needed to develop high‐capacity cathodes.…”

Study of Cathode Materials for Lithium-Ion Batteries: Recent Progress and New Challenges

“…Three main reduction processes (which accompany Li-intercalation) can be identified: Re1 at about 4.5 V is related to Li occupation in the tetrahedral sites; Re2 at 3.7 V can be ascribed to Li occupation in the octahedral sites corresponding to Ni 4+ /Ni 2+ and Co 4+ /Co 3+ ; and Re3 at <3.5 V can be explained by Li occupation in the octahedral sites associated with Mn 4+ /Mn 3+ redox [83,84]. Further delithiation beyond 4.5 V during the first cycle leads to oxygen vacancies and the subsequent migration of transition metal ions into lithium sites and lithium ions into tetrahedral sites, resulting in a distorted oxygen lattice [85][86][87][88]. Figure 11B,D shows that all the reduction peaks shift with cycling, but the shifting is more serious for 0.5Li 2 migration of transition metal ions into lithium sites and lithium ions into tetrahedral sites, resulting in a distorted oxygen lattice [85][86][87][88].…”