Xixi Shi

LiCoO2: recycling from spent batteries and regeneration with solid state synthesis

A green recycling process was designed and used to recycle spent LiCoO2 batteries, and the recycled LiCoO2 was regenerated after the solid state synthesis with Li2CO3. XRD results showed that the layered structure of LiCoO2 was repaired after regeneration. The physical and chemical properties (XRD, morphology, tap density, average particle size, specific surface areas and pH value) and electrochemical properties (discharge capacity, attenuation rate of capacity, plateau retention at 3.6 V and attenuation rate of plateau) of LiCoO2 after regeneration were tested in detail and compared with commercial LiCoO2. The test data show that the regenerated LiCoO2 at 900 °C can meet the commercial requirements for reuse.

A high energy density Li-rich positive-electrode material with superior performances via a dual chelating agent co-precipitation route

A new Li-rich positive-electrode Li1.13(Ni0.26Co0.09Mn0.52)O2 is successfully achieved via a dual ammonia and oxalate chelating agent co-precipitation route for the first time, which delivers a high volumetric energy density of over 2100 W h L−1, superior cycle life and stable high median-voltage. The dual or multiple chelating agent method gives a new insight towards high energy density for Li-rich materials with outstanding electrochemical performances for advanced lithium-ion batteries.

Understanding the Origin of Enhanced Performances in Core–Shell and Concentration-Gradient Layered Oxide Cathode Materials

Core-shell and concentration-gradient layered oxide cathode materials deliver superior electrochemical properties such as long cycle life and outstanding thermal stability. However, the origin of enhanced performance is not clear and seldom investigated until now. Here, a specific structured layered oxide (LiNi0.5Co0.2Mn0.3O2) consisting of concentration-gradient core, transition layer, and stable outer shell, is designed and achieved from double-shelled precursors to overcome the great challenge by comparison with the normal layered LiNi0.5Co0.2Mn0.3O2. As expected, the specific structured layered oxide displays excellent cycle life and thermal stability. After numerous cycles, the valence state of Ni and Co at normal layered oxide surface tends to a higher oxidation state than that of the specific structured oxide, and the spinel phase is observed on particle surface of normal layered oxide. Also, the deficient spinel/layered mixed phases lead to high surface film and charge-transfer resistance for normal layered oxide, whereas the specific structured one still remains a layered structure. Those results first illustrate the origin of improved electrochemical performance of layered core-shell and concentration-gradient cathode materials for lithium-ion batteries.

A novel core-concentration gradient-shelled LiNi0.5Co0.2Mn0.3O2 as high-performance cathode for lithium-ion batteries

A novel core-concentration gradient-shelled LiNi0.5Co0.2Mn0.3O2 was successfully synthesized for the first time by a simple method from core-shelled precursors [(Ni0.6Co0.2Mn0.2)1/2(Ni0.4Co0.2Mn0.4)1/2](OH)2 that were synthesized via a co-precipitation route. Particle size increase of hydroxide precursors from core to shell, in combination with subsequent investigations of Energy Disperse X-ray Spectrum (EDS) on precursors, supported the formation of a core-shelled structure. To obtain concentration gradient layer between core and shell, a high calcined temperature of 900 °C was selected as high temperature calcination gave rise to diffusion of cations in the core-shelled structure. Thus, the prepared precursor powders were then calcined with stoichiometric ratio lithium carbonate (Li/M = 1.05) at 900 °C in air, which resulted in core-concentration gradient-shelled (CCGS) LiNi0.5Co0.2Mn0.3O2. The compositions of core and shell separately were LiNi0.60Co0.20Mn0.20O2 and LiNi0.44Co0.20Mn0.36O2, between which was a concentration gradient layer. X-ray diffraction (XRD) studies show that the prepared material was indexed to a typical layered structure with a Rm space group. Compared to LiNi0.5Co0.2Mn0.3O2, the CCGS-LiNi0.5Co0.2Mn0.3O2 presented remarkably improved cycling performance and thermal stability, which can be ascribed to LiNi0.44Co0.20Mn0.36O2 shell providing structural and thermal stability.

Carbonate coprecipitation preparation of Li-rich layered oxides using the oxalate anion ligand as high-energy, high-power and durable cathode materials for lithium-ion batteries

Rechargeable lithium-ion batteries (LIBs) present an urgent demand to develop cathode materials that combine high-energy and high-power density with long cycle life. For meeting the demand, dual ligands (ammonia and oxalate anion) by hydroxide coprecipitation have been introduced to prepare spherical precursors for the above desired cathode in our previous study, in which low efficiency, toxic and volatile ammonia is still utilized as one of the ligands and an inert atmosphere is needed due to the high content of Mn. Thus, in this work, the feasibility of using the oxalate anion as a single ligand by carbonate coprecipitation for Li-rich layered oxides is investigated. Consequently, they deliver a high volumetric energy density of about 2000 W h L−1, a high-power density of over 940 W h L−1 at a current density of 1000 mA g−1, and superior cycling stability with a capacity retention of 98.1% after 80 cycles, indicating much better performances than the Li-rich oxides prepared via the ammonia ligand. Also, their performances approach the level for the sample prepared via dual ligands. The enhanced properties are likely ascribed to the smaller primary particles and the possibly suppressed phase transformation from layered to spinel phases due to a large amount of stacking faults, lower cation mixing and higher Mn oxidation state according to SEM, TEM, XRD and XPS experiments. These findings demonstrate that the oxalate anion is a desired ligand to prepare Li-rich layered oxides as high-energy, high-power and durable cathode materials for LIBs.

Synthesis and electrochemical characteristics of Li1.2(Ni0.2Mn0.6)x(Co0.4Mn0.4)y(Ni0.4Mn0.4)1−x−yO2 (0 ≤ x + y ≤ 1) cathode materials for lithium ion batteries

According to the tetrahedral phase diagram of LiNiO2–LiCoO2–LiMnO2–Li2MnO3, a series of Li1.2(Ni0.2Mn0.6)x(Co0.4Mn0.4)y(Ni0.4Mn0.4)1−x−yO2 (0 ≤ x + y ≤ 1) have been designed to explore new Li-rich solid solution cathode materials. The effects of Li1.2Ni0.2Mn0.6O2, Li1.2Co0.4Mn0.4O2 and Li1.2Ni0.4Mn0.4O2 content in solid solutions on structure and electrochemical properties are investigated. Micro-sized spherical or ellipsoidal precursors are first prepared via a carbonate co-precipitation route. After calcination with lithium sources, all samples are indexed to a typical layered structure with an Rm space group as detected by X-ray diffraction (XRD). It is found that the introduction of Co can improve the tap density. However, these Co referred samples reveal lower discharge specific capacities and inferior cycle life. For these Co-free materials with high Ni content, for instance Li1.2Ni0.3Mn0.5O2, although low capacity is observed in the initial cycle, a large capacity of above 250 mA h g−1 is achieved after about 10 cycles. Importantly, the activated Li1.2Ni0.3Mn0.5O2 material still delivers a high capacity of over 230 mA h g−1 after 70 cycles, displaying superior cycle stability. These results may be instructive in designing and exploring high performance cathode materials for advanced LIBs.

Improved Performances of LiNi0.8Co0.15Al0.05O2 Material Employing NaAlO2 as a New Aluminum Source

To prepare a high-performance LiNi0.8Co0.15Al0.05O2 material (LNCA) for Li-ion batteries, a new aluminum source, NaAlO2, is employed in the coprecipitation step for the first time, and the effect of aluminum sources on the performances is systematically investigated. Different from the traditional preparation process using Al(NO3)3 as the aluminum source, the preparation process of the Ni0.8Co0.15Al0.05(OH)2.05 precursor from NaAlO2 is a hydrolysis process, during which the fast precipitation of Al3+ and the formation of a flocculent precipitate can be effectively avoided. As expected, stoichiometric LNCA with uniform element distribution, low cation mixing and well-ordered layered structure is obtained from NaAlO2, which is designed as LNCA-NaAlO2. The characterization and electrochemical measurements show that LNCA-NaAlO2 exhibits significantly improved performances (such as tap density, initial discharge capacity and volumetric energy density, rate performance, cycle performance, electrochemical stability, microstructure stability, and storage stability) compared to the performances of those prepared from Al(NO3)3 (LNCA-Al(NO3)3), indicating that it is an effective strategy to preparing high-performance LNCA employing NaAlO2 as the aluminum source.

Unravelling the Structure and Electrochemical Performance of Li–Cr–Mn–O Cathodes: From Spinel to Layered

To explore a new series of cathode materials with high electrochemical performance, the spinel-layered (1 - x)[LiCrMnO4]· x[Li2MnO3·LiCrO2] ( x = 0, 0.25, 0.5, 0.75, and 1) composites are synthesized with the sol-gel method. X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction, and Raman spectra reveal that the structure of the (1 - x)[LiCrMnO4]· x[Li2MnO3·LiCrO2] cathode materials evolves from spinel to hybrid spinel-layered and layered structures with the increase of the Li concentration. Test results reveal that the structure and electrochemical performance of (1 - x)[LiCrMnO4]· x[Li2MnO3·LiCrO2] ( x = 0.25, 0.5 and 0.75) composites have the characteristics of both spinel ( x = 0) and Li-rich layered phases ( x = 1). In particular, x = 0.5 and 0.75 electrodes exhibit relatively high capacity retention and rate capability, which is mainly ascribed to the synergistic effect of the spinel and Li-rich layered phases, the 3D Li-ion diffusion channels of the spinel phase, and the low charge-transfer resistance ( Rct) and Warburg diffusion impedance ( Wo).

The effect of lithium content on the structure, morphology and electrochemical performance of Li-rich cathode materials Li1+x(Ni1/6Co1/6Mn4/6)1−xO2

Spherical Li-rich cathode materials Li1+x(Ni1/6Co1/6Mn4/6)1−xO2 (x = 0.130, 0.167, 0.200, 0.231) are synthesized via co-precipitation and solid state reaction, and the effect of lithium content on their structure, morphology and electrochemical performance is investigated. XRD shows that the more lithium content, the more superlattice the structure of the monoclinic Li2MnO3-like component. Besides, as the lithium content increases, the spherical morphology changes little, but the primary particle size increases and the secondary particle surface becomes rough. Among these Li-rich cathode materials, Li1+x(Ni1/6Co1/6Mn4/6)1−xO2 (x = 0.167) displays the highest tap density (over 2.3 g cm−3) and the best electrochemical performance (an initial discharge capacity of 274.1 mA h g−1 in the voltage range of 2.0–4.8 V at 0.1C, a capacity retention of 83.1% after 80 cycles and the highest initial volumetric energy densities of 2277 W h L−1). This is possibly associated with the dense morphology and low cation disordering of Li and Mn in the transition metal layers, which is closely related to the lithium content. This research is expected to definitely contribute to improving the electrochemical performance of Li-rich layered electrodes and making Li-rich materials viable for practical applications in advanced Li-ion batteries.

Influence of Ni/Mn distributions on the structure and electrochemical properties of Ni-rich cathode material

To reveal the influence of element distribution on the structure and electrochemical performances of Ni-rich layered cathode materials, LiNi0.68Co0.13Mn0.19O2 (NCM) with four types of Ni/Mn distributions (homogeneous, core-shell, multi-shell and concentration-gradient structures) is designed and synthesized with a combination of co-precipitation and high-temperature solid-state method. Ni/Mn distributions of the as-prepared NCM cathode materials are investigated with focused ion beam (FIB) and energy disperse X-ray spectrum (EDS) line scanning on the cross-section of single particles, which illustrate that NCM materials with the desired Ni/Mn distributions are successfully prepared. For the three spherical heterogeneous NCM materials, the center is the Ni-rich component while the surface is the Mn-rich component. Ni/Mn distributions between the center and surface components are in different forms. Studies imply that the heterogeneous samples exhibit smaller cation disordering, lower charge transfer resistance, higher Li+ diffusion coefficient and higher structural stability than the homogeneous one. Therefore, the heterogeneous samples, especially the multi-shell and concentration-gradient ones, display improved cycling and thermal stability compared to the homogeneous one. These results manifest that multi-shell and concentration-gradient structures are effective strategies to modify the layered NCM cathode materials for Li-ion batteries.