Exploring the Nanoscale Origin of Performance Enhancement in Li_1.1Ni_0.35Mn_0.55O₂ Batteries Due to Chemical Doping

Abstract

While cathode materials with a layered structure containing Co such as LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC111) can currently provide high capacities, their use for next-generation Li-ion batteries is limited by the high toxicity, cost, and ethical issues associated with cobalt mining. [3,4] Due to the strategic importance of Co reduction or elimination, a wide range of alternative compounds and lithium chemistries are currently being researched; [5] however, most of these exhibit significant drawbacks compared to NMC111. For example, olivine (LiFePO 4 ) [6] and spinel (LiNi 0.5 Mn 1.5 O 4 ) [7] based materials have interesting properties such as being Co-free, low cost and presenting high C-rate performance for rapid battery charging, but their capacity is limited to <200 mAhg −1 . Ni-rich layered oxides with low cobalt content, for example, LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) and LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) deliver high energy densities but suffer from slow kinetics and poor cycling stability requiring complex engineering at the particle level to enhance performance. [8,9] Additionally, these materials are prone to reactivity and instability upon exposure to ambient conditions [10] and their price has increased lately.In addition to the aforementioned compounds, it is also possible to fabricate Co-free cathode materials based off the layered Li-Mn-rich oxides. These form complex nanocomposite structures due to their nanoscale integration of two structural components: a monoclinic C2/m Li 2 MnO 3 -like phase (M-phase) and a rhombohedral R-3m LiMn 1/2 Ni 1/2 O 2 -like phase (R-phase). [11,12] The presence of both structures as a nanocomposite material is desirable, as they differ in their cation ordering and are active at different potentials up to 4.6 V versus Li + /Li, thereby maximizing energy density. However, without the inclusion of Co, these nanocomposites show limited capacity retention, poor efficiencies, severe voltage fade, and a failure to deliver capacity at high C-rates. [13,14] Several approaches have been discussed in the literature to improve the performance of this system, and some of the most promising results have been obtained by chemical doping. [13,15,16] For instance, Al-doped samples showed superior cycling performance and lower voltage decay than parent compositions, [17][18][19] which was attributed to a robust R-phase stabilizing the overall structure while blocking the random growth of spinel-like phases. [17] The effect Despite significant potential as energy storage materials for electric vehicles due to their combination of high energy density per unit cost and reduced environmental and ethical concerns, Co-free lithium ion batteries based on layered Mn oxides presently lack the longevity and stability of their Co-containing counterparts. Here, a reduction in this performance gap is demonstrated via chemical doping, with Li 1.1 Ni 0.35 Mn 0.54 Al 0.01 O 2 achieving an initial discharge capacity of 159 mAhg −1 at C/3 rate and a corresponding capacity retention of 94.3% after 150 ...

Phase Engineering via Aluminum Doping Enhances the Electrochemical Stability of Lithium‐Rich Cobalt‐Free Layered Oxides for Lithium‐Ion Batteries

“…Several dopants have been reported to stabilize the crystal structure of Li-rich layered oxides, including Ti/Zr, [11] Sb, [12] Nb, [13,14] Ru, [15] Fe, [16,17] and Al. [1,[18][19][20][21][22][23][24] The latter has received particular attention because of its positive influence on both capacity and voltage stability. Nayak et al [20] doped lithium-rich Li 1.2 Ni 0.16 Mn 0.56 Co 0.08 O 2 with Al, mitigating voltage fade and improving the capacity retention from 68% to 96% (100 cycles, C/10).…”

“…Several dopants have been reported to stabilize the crystal structure of Li‐rich layered oxides, including Ti/Zr, [ 11 ] Sb, [ 12 ] Nb, [ 13,14 ] Ru, [ 15 ] Fe, [ 16,17 ] and Al. [ 1,18–24 ] The latter has received particular attention because of its positive influence on both capacity and voltage stability. Nayak et al.…”

“…Turning to Co‐free compositions, doping a small amount of Al in Li 1.1 Ni 0.35 Mn 0.55 O 2 led to the formation of unobstructed lithium ion diffusion pathways and a structural stabilization effect, improving the capacity retention to 94.3% after 150 cycles (C/3). [ 24 ] The Li 1.275 Al 0.075 Mn 0.55 Ni 0.45 O 2.5 composition reported by Yin et al. [ 23 ] retained 92.9% of its initial capacity of ≈200 mAh g −1 after 200 cycles at 1 C, owing to the microporous structure of the secondary particles alleviating stress issues during electrochemical operation.…”

Construction of a label-free electrochemical immunosensor based on a Co9S8/Co3C@C dual-heterojunction for the detection of diethylstilbestrol

“…Through the contact, electrons are transferred until the work functions are equal. 34,35 Chemical doping, 36 nanostructure engineering, 37 and construction of hybrids 38 are all viable strategies for fulfilling the fabrication of heterostructures. It consequently seems extremely positive to combine alternative construction approaches to create heterostructures.…”