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Nickel-rich layered lithium transition-metal oxides, LiNi(1-x)M(x)O(2) (M = transition metal), have been under intense investigation as high-energy cathode materials for rechargeable lithium batteries because of their high specific capacity and relatively low cost. However, the commercial deployment of nickel-rich oxides has been severely hindered by their intrinsic poor thermal stability at the fully charged state and insufficient cycle life, especially at elevated temperatures. Here, we report a nickel-rich lithium transition-metal oxide with a very high capacity (215 mA h g(-1)), where the nickel concentration decreases linearly whereas the manganese concentration increases linearly from the centre to the outer layer of each particle. Using this nano-functional full-gradient approach, we are able to harness the high energy density of the nickel-rich core and the high thermal stability and long life of the manganese-rich outer layers. Moreover, the micrometre-size secondary particles of this cathode material are composed of aligned needle-like nanosize primary particles, resulting in a high rate capability. The experimental results suggest that this nano-functional full-gradient cathode material is promising for applications that require high energy, long calendar life and excellent abuse tolerance such as electric vehicles.

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We have developed a novel cathode material based on lithium−nickel−manganese−cobalt oxide, where the manganese concentration remains constant throughout the particle, while the nickel concentration decreases linearly and the cobalt concentration increases from the center to the outer surface of the particle. This full concentration gradient material with a fixed manganese composition (FCG−Mn-F) has an average composition of Li[Ni 0.60 Co 0.15 Mn 0.25 ]O 2 and is composed of rod-shaped primary particles whose length reaches 2.5 μm, growing in the radial direction. In cell tests, the FCG−Mn-F material delivered a high capacity of 206 mAh g −1 with excellent capacity retention of 70.3% after 1000 cycles at 55 °C. This cathode material also exhibited outstanding rate capability, good low-temperature performance, and excellent safety, compared to a conventional cathode having the same composition (Li[Ni 0.60 Co 0.15 Mn 0.25 ]O 2 ), where the concentration of the metals is constant across the particles.

The electrochemical properties and thermal stabilities of a new positive electrode material for Li-ion batteries, Li͓Ni 0.55 Co 0.15 Mn 0.30 ͔O 2 , were investigated over a wide potential window. This electrode material was synthesized via a coprecipitation method. X-ray diffraction studies indicated that the synthesized material crystallized into an ␣-NaFeO 2 layered structure ͑R3m͒. The Li͓Ni 0.55 Co 0.15 Mn 0.30 ͔O 2 positive electrode has a discharge capacity of 202 mAh g −1 in the voltage range of 2.7-4.5 V. This high capacity was retained throughout cycling. The thermal stability of Li͓Ni 0.55 Co 0.15 Mn 0.30 ͔O 2 was measured by differential thermal calorimetry and found to be comparable to that of Li͓Ni 1/3 Co 1/3 Mn 1/3 ͔O 2 . This positive electrode material was also characterized in a full cell configuration ͑graphite negative electrode͒ by the hybrid pulse power characterization tests following the FreedomCAR battery test manual for plug-in hybrid electric vehicles ͑PHEVs͒. The pulse power capability and available energy met the goals for PHEVs.