time further and enhance power density during acceleration process so as to perfect its practicality. [1b,3] Electrode materials (cathode and anode) play an important role in the electrochemical properties of LIBs, including energy-density, cycle-life, rate capability, and safety among others. Graphite materials with high capacity greater than 300 mAh g −1 , superior structural stability, as well as low cost are significantly applied as anode electrode in commercialized LIBs. [4] The other anode, graphite/silicon composites that can deliver higher capacity of around 1000 mAh g −1 and that of pure graphite electrode are gradually commercialized to further enhance the energy density of LIBs. [5] The first commercial cathode material, layered oxide LiCoO 2 with O3 structure (in which oxygen anion have a cubic close packing arrangement in the form of ABCABC…), illustrates the unpleasant transformation from hexagonal phase to monoclinic phase, particularly when the Li + deintercalation ratio (x) exceeds 0.5 in Li 1−x CoO 2 . [6] This is in contrast with graphite-based anode with preferred electrochemical performance and low cost. Also, this phase transition derived from the order/disorder transformation of Li + is anticipated to cause rapid decay of reversible capacity. [6d] Consequently, the LiCoO 2 cathode can only deliver around 150 mAh g −1 , which has limi ted the performance promotion of LIBs and the far-ranging applications of LIBs in PHEVs and EVs.Additionally, developing high-capacity (energy-density) cathode materials with desired electrochemical behaviors in place of the conventional LiCoO 2 has been the main motivation behind LIBs in the recent past. Three main groups of cathode materials, layered oxides including lithium-stoichiometric Li[Ni x Co y Mn 1−x−y ]O 2 and lithium-rich Li 1+z M 1−z O 2 (M = Mn, Ni, Co, Ru, Sn, Ir, etc.), spinel LiM 2 O 4 (M = Ni, Mn), together with olive LiMXO 4 (M = Fe, Mn, Co; X = P, Si) as illustrated in Figure 1, are broadly examined as the next-generation cathode materials for LIBs. [3a,6e,7] Among these candidates lithiumrich and manganese-based layered oxides display the highest energy-density of approach 1000 Wh Kg −1 as a result of the large reversible capacity of ≈300 mAh g −1 and high voltage of 3.5 V (vs. Li/Li + ). However, there are various significantThe urgent prerequisites of high energy-density and superior electrochemical properties have been the main inspiration for the advancement of cathode materials in lithium-ion batteries (LIBs) in the last two decades. Nickel-rich layered transition-metal oxides with large reversible capacity as well as high operating voltage are considered as the most promising candidate for next-generation LIBs. Nonetheless, the poor long-term cycle-life and inferior thermal stability have limited their broadly practical applications. In the research of LIBs, it is observed that surface/interfacial structure and chemistry play significant roles in the performance of cathode cycling. This is due to the fact that they are basical...

In this review, the design principles, formation mechanism and recent advances in co-precipitation preparation core–shell and concentration-gradient cathodes for advanced LIBs are summarized. The remaining challenges and possible solutions are also discussed.

The unstable electrode/electrolyte interface of high-capacity LiNiCoAlO (NCA) cathodes, especially at a highly delithiated state, usually leads to the transformation of layered to spinel and/or rock-salt phases, resulting in drastic capacity fade and poor thermal stability. Herein, the Al-increased and Ni-,Co-decreased electrode surface is fabricated through tailoring element distribution in micrometer-sized spherical NCA secondary particles via coprecipitation and solid-state reactions, aimed at stabilizing the electrode/electrolyte interface during continuous cycles. As expected, it shows much extended cycle life, 93.6% capacity retention within 100 cycles, compared with that of 78.5% for the normal NCA. It also delivers large reversible capacity of about 140 mAh g even at 20 C, corresponding to energy density of around 480 Wh kg, which is enhanced by 45% compared to that of the normal NCA (about 330 Wh kg). Besides, the delayed heat emission temperature and reduced heat generation mean remarkably improved thermal stability. These foregoing improvements are ascribed to the Al-increased spherical secondary particle surface that stabilizes the electrode/electrolyte interface by protecting inner components from directly contacting with electrolyte and suppressing the side reaction on electrode surface between high oxidizing Ni and electrolyte.

A full concentration-gradient layered oxide presents excellent cycle stability and thermal stability as compared with a normal oxide due to the stable structure with low Ni content on the surface layer.