Li[Ni0.65Co0.13Mn0.22]O2 cathode with two‐sloped full concentration gradient (TSFCG), maximizing the Ni content in the inner part of the particle and the Mn content near the particle surface, is synthesized via a specially designed batch‐type reactor. The cathode delivers a discharge capacity of 200 mAh g−1 (4.3 V cutoff) with excellent capacity retention of 88% after 1500 cycles in a full‐cell configuration. Overall electrochemical performance of the TSFCG cathode is benchmarked against conventional cathode (CC) with same composition and commercially available Li[Ni0.8Co0.15Al0.05]O2 (NCA). The TSFCG cathode exhibits the best cycling stability, rate capability, and thermal stability of the three electrodes. Transmission electron microscopy analysis of the cycled TSFCG, CC, and NCA cathodes shows that the TSFCG electrode maintains both its mechanical and structural integrity whereas the NCA electrode nearly pulverizes due to the strain during cycling.
LiNiO 2 with theoretical capacity of 275 mAh g −1 is regarded as a promising cathode material for Li-ion batteries, but its potential capacity has not been fully realized due to the severe capacity loss in the first charge/discharge cycle. Via co-precipitation method, we synthesized Li[Ni 0.90 Co 0.05 Mn 0.05 ]O 2, Li[Ni 0.95 Co 0.025 Mn 0.025 ]O 2 , and LiNiO 2 which delivered 221, 230, and 240 mAh g −1 , respectively, when cycled from 2.7 to 4.3 V vs. Li 0 /Li + at 0.1 C and retained ∼70% of the initial capacity after 100 cycles. To date, such high reversible capacities are not yet to be reported from the Ni-rich Li[Ni 1−x−y Co x Mn y ]O 2 cathodes. The observed high capacities were attributed to the presence of a rock salt phase from severe cation mixing and excess Li ions in the host structure. It is believed that the rock salt phase stabilized the host structure in the delithiated state while the excess Li allowed the Li ions percolated through the rock salt phase which would be electrochemically inactive otherwise.Lithium nickel oxide, LiNiO 2 , with isostructural with NaFeO 2 , was firstly reported by Dyer et al. in 1954. 1 Since the commercialization of lithium-ion battery by Sony in 1991, LiNiO 2 has been extensively studied to replace LiCoO 2 because of its higher capacity and lower cost. However, it has been well-known that synthesis of stoichiometric LiNiO 2 is very difficult since Ni 2+ with similar ionic radius as Li + ends up in the Li + sites to form of Li 1-x Ni 1+x O 2 (0.0 ≤ x ≤ 0.2), or more precisely [Li 1-x Ni x ]3a[Ni]3b[O 2 ]6c 2,3 during the high temperature calcination of stoichiometric LiNiO 2 . The substituted Ni in the lithium layer hinders the Li + diffusion and thus greatly decreases electrochemical performances. 4 Ohzuku et al. reported that an integrated intensity ratio of I(003)/I(104) had a strong relation with the displacement of nickel ions and lithium ions which was correlated to the electrochemical reactivity of the LiNiO 2 ; 5 the higher intensity ratio of the I(003)/I(104) reduced the cation mixing and thus results in a high capacity and good Li + intercalation stability. A stoichiometric LiNiO 2 synthesized by excess Li method showed discharge capacity of more than 200 mAh g −1 when cycled between 3.0 and 4.5 V. 2,6 However, all the synthesized LiNiO 2 have exhibited reduction in capacity and poor cycling performance when the upper cutoff potential was reduced to 4.3 V. 7 It is likely that a high concentration of unstable Ni 4+ in the highly delithated Li x NiO 2 was easily transformed to more stable and insulting NiO phase, leading to high interfacial impedance and thus resulting in poor electrochemical performance. 2,7,8 The structural changes of Li 1-x NiO 2 occurring during charging and discharging were intensively studied by X-ray diffraction analysis to identify the relationship between the phase transition and the Li + intercalation stability. 2,6,8,9 Ohzuku et al. did ex-situ XRD study on the Li 1-x NiO 2 on 1 st charge and discharge processes and reported that t...
Compositionally graded Li[Ni 0.84 Co 0.06 Mn 0.09 Al 0.01 ]O 2 (TSFCG-Al) with two-step concentration gradients was prepared as a high-capacity cathode for Li batteries. The concentration gradients were introduced within a single particle to maximize the Ni fraction; this increased the discharge capacity while ensuring cyclic stability with a Mn-enriched surface layer. The concentration gradients also produced a unique morphology, in which rodshaped primary particles were radially aligned in a spoke-like pattern. The fundamental electrochemical performance of TSFCG-Al is compared against that of commercial Li[Ni 0.85 Co 0.11 Al 0.04 ]O 2 (NCA). The TSFCG-Al cathode exhibits a higher discharge capacity and better cycling stability than the NCA cathode, even when they are charged to 4.5 V. Structural analysis of the cycled TSFCG-Al and NCA cathodes shows that the TSFCG-Al keeps its original structural integrity, while the NCA particles undergo serious particle degradation due to the accumulation of strain in the grain boundaries upon cycling.
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