Fast development of portable electronic devices (such as a smart phone, iPad, and Galaxy Note) and electrified vehicles (such as EVs and HEVs) require better and smaller lithium ion batteries as their energy storages. What is needed for the cathode of the lithium ion battery is a material capable of higher energy density. However, not only the development of cathode material but also the commercialization of high energy density anode material has been limited due to the cathode material’s much lower energy density compared to anode material. In this regard, Li-rich material (Li₂MnO₃-LiMO₂, M=Ni, Mn and Co) that has 150 % higher energy density than commercialized LiCoO­₂ is the unique next generation cathode material to solve the problem. In the past decade, many researches have focused on the surface stabilization method of this material to improve its intrinsic problems of poor cycle/ rate capability and such surface treatment methods have been demonstrated in a few examples, including AlF₃ coating and spinel heterostructures, yielding noticeable improvements in rate and cycle ability. Although such surface treatments showed improved rate and cycle performances, the realization of the Li-rich material’s high volumetric energy density and long-term cycle life which are more critical factors for the commercialization of Li-rich material still remained unsatisfied. For instance, AlF₃ coated Li-rich LNCMO has abrupt capacity fade after 100 cycles, while it showed good rate and cycle capability within 100 cycles. Hence, new active material design, instead of simple surface modification methods such as coating or doping, is required to solve above previous limits.

Here we demonstrate a novel approach for lithium storage, which is a material design of a secondary structure which consists of large primary particle with a novel activation method using simple chemical treatment, to achieve superior long-term cycle life with high volumetric energy density. In this design, the large primary particle effectively reduced its surface area producing markedly decreased surface instability reaction as well as high tap density. Interestingly, the chemical approach activates only surface Li₂MnO₃ phase of large primary particle and the very surface activation effectively overcome the activation problem, which is limit of large primary particle have. This novel concept is very meaningful in that it is the first and unique method to achieve cathode material’s high volumetric energy density with long-term cycle life. As a result, this novel designed material affords remarkable battery performance with high volumetric energy density of ~1980 Wh L^-1 and extremely high cycle retention of 90% during 300 cycles.