Improved Cycling Stability of Li[Ni0.90Co0.05Mn0.05]O2 Through Microstructure Modification by Boron Doping for Li‐Ion Batteries

Boron‐doped Li[Ni_0.90Co_0.05Mn_0.05]O₂ cathodes are synthesized by adding B₂O₃ during the lithiation of the hydroxide precursor. Density functional theory confirms that boron doping at a level as low as 1 mol% alters the surface energies to produce a highly textured microstructure that can partially relieve the intrinsic internal strain generated during the deep charging of Li[Ni_0.90Co_0.05Mn_0.05]O₂. The 1 mol% B‐Li[Ni_0.90Co_0.05Mn_0.05]O₂ cathode thus delivers a discharge capacity of 237 mAh g^?1 at 4.3 V, with an outstanding capacity retention of 91% after 100 cycles at 55 °C, which is 15% higher than that of the undoped Li[Ni_0.90Co_0.05Mn_0.05]O₂ cathode. This proposed synthesis strategy demonstrates that an optimal microstructure exists for extending the cycle life of Ni‐rich Li[Ni_1‐x‐yCo_xMn_y]O₂ cathodes that have an inadequate cycling stability in electric vehicle applications and indicates that an optimal microstructure can be achieved through surface energy modification.     

High‐Capacity Concentration Gradient Li[Ni0.865Co0.120Al0.015]O2 Cathode for Lithium‐Ion Batteries

A Ni‐rich concentration‐gradient Li[Ni_0.865Co_0.120Al_0.015]O₂ (NCA) cathode is prepared with a Ni‐rich core to maximize the discharge capacity and a Co‐rich particle surface to provide structural and chemical stability. Compared to the conventional NCA cathode with a uniform composition, the gradient NCA cathode exhibits improved capacity retention and better thermal stability. Even more remarkably, the gradient NCA cathode maintains 90% of its initial capacity after 100 cycles when cycled at 60 °C, whereas the conventional cathode exhibits poor capacity retention and suffers severe structural deterioration. The superior cycling stability of the gradient NCA cathode largely stemmed from the gradient structure combines with the Co‐rich surface, which provides chemical stability against electrolyte attack and reduces the inherent internal strain observed in all Ni‐rich layered cathodes in their charged state, thus providing structural stability against the repeated anisotropic volume changes during cycling. The high discharge capacity of the proposed gradient NCA cathode extends the driving range of electric vehicles and reduces battery costs. Furthermore, its excellent capacity retention guarantees a long battery life. Therefore, gradient NCA cathodes represent one of the best classes of cathode materials for electric vehicle applications that should satisfy the demands of future electric vehicles.     

Synthesis and Characterization of Lithium Bis(fluoromalonato)borate for Lithium‐Ion Battery Applications

A new orthochelated salt, lithium bis(monofluoromalonato)borate (LiBFMB), is synthesized and purified for application in lithium‐ion batteries. The presence of fluorine in the borate anion of LiBFMB increases its oxidation potential and also facilitates ion dissociation, as reflected by the ratio of ionic conductivity (σ_exp) and ion diffusivity coefficients (σ_NMR). Half‐cell tests using 5.0 V lithium nickel manganese oxide (LiNi_0.5Mn_1.5O₄) as a cathode and ethylene carbonate (EC)/dimethyl carbonate (DMC)/diethyl carbonate (DEC) as a solvent reveals that the impedance of the LiBFMB cell is much larger than those of LiPF₆‐ and lithium bis(oxalato)borate (LiBOB)‐based cells, which results in lower capacity and poor cycling performance of the former. X‐ray photoelectron spectroscopy (XPS) results for the cycled cathode electrode suggest that because of the stability of the LiBFMB salt, the solid electrolyte interphase (SEI) formed on the cathode surface is significantly different from those of LiPF₆ and LiBOB based electrolytes, resulting in more solvent decomposition and a thicker SEI layer. Initial results also indicate that using a high dielectric constant solvent, propylene carbonate, alters the surface chemistry, reduces the interfacial impedance, and enhances the performance of LiBFMB‐based 5.0 V cell.     

ZnFe2O4‐C/LiFePO4‐CNT: A Novel High‐Power Lithium‐Ion Battery with Excellent Cycling Performance

An innovative and environmentally friendly battery chemistry is proposed for high power applications. A carbon‐coated ZnFe₂O₄ nanoparticle‐based anode and a LiFePO₄‐multiwalled carbon nanotube‐based cathode, both aqueous processed with Na‐carboxymethyl cellulose, are combined, for the first time, in a Li‐ion full cell with exceptional electrochemical performance. Such novel battery shows remarkable rate capabilities, delivering 50% of its nominal capacity at currents corresponding to ≈20C (with respect to the limiting cathode). Furthermore, the pre‐lithiation of the negative electrode offers the possibility of tuning the cell potential and, therefore, achieving remarkable gravimetric energy and power density values of 202 Wh kg^?1 and 3.72 W kg^?1, respectively, in addition to grant a lithium reservoir. The high reversibility of the system enables sustaining more than 10 000 cycles at elevated C‐rates (≈10C with respect to the LiFePO₄ cathode), while retaining up to 85% of its initial capacity.     

Grafting Benzenediazonium Tetrafluoroborate onto LiNixCoyMnzO2 Materials Achieves Subzero‐Temperature High‐Capacity Lithium‐Ion Storage via a Diazonium Soft‐Chemistry Method

Subzero‐temperature Li‐ion batteries (LIBs) are highly important for specific energy storage applications. Although the nickel‐rich layered lithium transition metal oxides(LiNi_xCo_yMn_zO₂) (LNCM) (x > 0.5, x + y +z = 1) are promising cathode materials for LIBs, their very slow Li‐ion diffusion is a main hurdle on the way to achieve high‐performance subzero‐temperature LIBs. Here, a class of low‐temperature organic/inorganic hybrid cathode materials for LIBs, prepared by grafting a conducting polymer coating on the surface of 3 µm sized LiNi_0.6Co_0.2Mn_0.2O₂ (LNCM‐3) material particles via a greener diazonium soft‐chemistry method is reported. Specifically, LNCM‐3 particles are uniformly coated with a thin polyphenylene film via the spontaneous reaction between LNCM‐3 and C₆H₅N₂⁺BF₄^?. Compared with the uncoated one, the polyphenylene‐coated LNCM‐3 (polyphenylene/LNCM‐3) has shown much improved low‐temperature discharge capacity (≈148 mAh g^?1 at 0.1 C, ?20 °C), outstanding rate capability (≈105 mAh g^?1 at 1 C, ?20 °C), and superior low‐temperature long‐term cycling stability (capacity retention is up to 90% at 0.5 C over 1150 cycles). The low‐temperature performance of polyphenylene/LNCM‐3 is the best among the reported state‐of‐the art cathode materials for LIBs. The present strategy opens up a new avenue to construct advanced cathode materials for wider range applications.     

Reducing Capacity and Voltage Decay of Co‐Free Li1.2Ni0.2Mn0.6O2 as Positive Electrode Material for Lithium Batteries Employing an Ionic Liquid‐Based Electrolyte

Lithium‐rich layered oxides (LRLOs) exhibit specific capacities above 250 mAh g^?1, i.e., higher than any of the commercially employed lithium‐ion‐positive electrode materials. Such high capacities result in high specific energies, meeting the tough requirements for electric vehicle applications. However, LRLOs generally suffer from severe capacity and voltage fading, originating from undesired structural transformations during cycling. Herein, the eco‐friendly, cobalt‐free Li_1.2Ni_0.2Mn_0.6O₂ (LRNM), offering a specific energy above 800 Wh kg^?1 at 0.1 C, is investigated in combination with a lithium metal anode and a room temperature ionic liquid‐based electrolyte, i.e., lithium bis(trifluoromethanesulfonyl)imide and N‐butyl‐N‐methylpyrrolidinium bis(fluorosulfonyl)imide. As evidenced by electrochemical performance and high‐resolution transmission electron microscopy, X‐ray photoelectron spectroscopy, and online differential electrochemical mass spectrometry characterization, this electrolyte is capable of suppressing the structural transformation of the positive electrode material, resulting in enhanced cycling stability compared to conventional carbonate‐based electrolytes. Practically, the capacity and voltage fading are significantly limited to only 19% and 3% (i.e., lower than 0.2 mV per cycle), respectively, after 500 cycles. Finally, the beneficial effect of the ionic liquid‐based electrolyte is validated in lithium‐ion cells employing LRNM and Li₄Ti₅O₁₂. These cells achieve a promising capacity retention of 80% after 500 cycles at 1 C.     

Ambient‐Pressure Relithiation of Degraded LixNi0.5Co0.2Mn0.3O2 (0 < x < 1) via Eutectic Solutions for Direct Regeneration of Lithium‐Ion Battery Cathodes

With the rapid growth of the lithium‐ion battery (LIBs) market, recycling and re‐use of end‐of‐life LIBs to reclaim lithium (Li) and transition metal (TM) resources (e.g., Co, Ni), as well as eliminating pollution from disposal of waste batteries, has become an urgent task. Here, for the first time the ambient‐pressure relithiation of degraded LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) cathodes via eutectic Li⁺ molten‐salt solutions is successfully demonstrated. Combining such a low‐temperature relithiation process with a well‐designed thermal annealing step, NCM523 cathode particles with significant Li loss (≈40%) and capacity degradation (≈50%) can be successfully regenerated to achieve their original composition and crystal structures, leading to effective recovery of their capacity, cycling stability, and rate capability to the levels of the pristine materials. Advanced characterization tools including atomic resolution electron microscopy imaging and electron energy loss spectroscopy are combined to demonstrate that NCM523's original layered crystal structure is recovered. For the first time, it is shown that layer‐to‐rock salt phase change on the surfaces and subsurfaces of the cathode materials can be reversed if lithium can be incorporated back to the material. The result suggests the great promise of using eutectic Li⁺ molten–salt solutions for ambient‐pressure relithiation to recycle and remanufacture degraded LIB cathode materials.     

Carbon Coated ZnFe2O4 Nanoparticles for Advanced Lithium‐Ion Anodes

The preparation and electrochemical characterization of a new material consisting of carbon coated ZnFe₂O₄ nanoparticles is presented. This material, which offers an interesting combination of alloying and conversion mechanisms, is capable of hosting up to nine equivalents of lithium per unit formula, corresponding to an exceptional specific capacity, higher than 1000 mAh g^?1. Composite electrodes of such a material, prepared using environmentally friendly sodium carboxymethyl cellulose as binder, showed the highest, ever reported, specific capacity and high rate performance upon long‐term testing. Furthermore, in situ X‐ray diffraction analysis allowed identifying the reduction process occurring upon initial lithiation.     

Surface Mn Oxidation State Controlled Spinel LiMn2O4 as a Cathode Material for High‐Energy Li‐Ion Batteries

Spinel lithium manganese oxide (LiMn₂O₄) has attracted much attention as a promising cathode material for large‐scale lithium ion batteries. However, its continuous capacity fading at elevated temperature is an obstacle to extended cycling in large‐scale applications. Here, surface Mn oxidation state controlled LiMn₂O₄ is synthesized by coating stoichiometric LiMn₂O₄ with a cobalt‐substituted spinel, for which stoichiometric LiMn₂O₄ is used as the starting material and onto which a Li_xMn_yCo_zO₄ layer is coated from an acetate‐based precursor solution. In the coated material, the concentrations of both cobalt and Mn⁴⁺ ions vary from the surface to the core. the former without any lattice mismatch between the coating layer and host material. Cycle tests are performed under severe conditions, namely, high temperature and intermittent high current load. During the first discharge cycle at 7 C and 60 °C, a high energy and power density are measured for the coated material, 419 and 3.16 Wh kg^?1, respectively, compared with 343 and 3.03 Wh kg^?1, respectively, for the bare material. After 65 cycles under severe conditions, the coated material retains 82% and ≈100% of the initial energy and power density, respectively, whereas the bare material retains only ≈68% and ≈97% thereof.     

High Performance Na0.5[Ni0.23Fe0.13Mn0.63]O2 Cathode for Sodium‐Ion Batteries

The synthesis of a new layered cathode material, Na_0.5[Ni_0.23Fe_0.13Mn_0.63]O₂, and its characterization in terms of crystalline structure and electrochemical performance in a sodium cell is reported. X‐ray diffraction studies and high resolution scanning electron microscopy images reveal a well‐defined P2‐type layered structure, while the electrochemical tests demonstrate excellent characteristics in terms of high capacity and cycle life. This performance, the low cost, and the environmental compatibility of its component poses Na_0.5[Ni_0.23Fe_0.13Mn_0.63]O₂ to be among the most promising materials for the next generation of sodium‐ion batteries.