Enhancing Surface Chemical Stability of LiMn2 O4 Cathode by Strontium Enrichment at Grain Boundaries.

LiMn2 O4 (LMO) cathodes suffer from limited cycle life, resulting from Mn dissolution and side reactions between electrode and electrolyte. In this study, Sr-modified LMO is prepared by using a simple strategy. The nature and position of large-radius Sr ions are investigated, alongside their influence on the structural stability of the bulk. SrMnO3 (SMO) is found to be enriched at grain boundaries of LMO, with Mn-O-Sr bonds forming at the SMO/LMO interface. Furthermore, stable SMO alleviates the migration of Mn ions in LMO associated with structural integrity and suppresses side reactions between the electrode and electrolyte. The modified LMO cathodes maintain their structural integrity and display improved rate performance and cycling stability under harsh conditions. Remarkably, the discharge capacity of a Sr-modified LMO||Li half-cell maintains 94.8 % at 25 °C and 79.6 % at 55 °C after 500 cycles. Consequently, enrichment of strontium at grain boundaries presents a promising strategy for developing cathodes for long-term use.

Surface Architecture Design of LiNi0.8 Co0.15 Al0.05 O2 Cathode with Synergistic Organics Encapsulation to Enhance Electrochemical Stability.

Ni-rich LiNi0.8 Co0.15 Al0.05 O2 (NCA) material attracts extensive attention due to its high discharge specific capacity, but its distinct drawbacks of rapid capacity decline and poor cycle performance at elevated temperatures and high voltage during charge/discharge cycling restricts its widespread application. To solve these problems, a multifunctional coating layer composed of a lithium-ion-conductive lithium polyacrylate (LiPAA) inner layer and a cross-linked polymer outer layer from certain organic substances of silane-coupling agent (KH550) and polyacrylic acid (PAA) is successfully designed on the surface of NCA materials, which is favorable for eliminating residual lithium and improving lithium-ion conductivity, surface stability, and hydrophobicity of NCA materials. In addition, the amount of the coating material is also investigated. A series of characterization methods such as XRD, FTIR, SEM, TEM, and X-ray photoelectron spectroscopy are used to analyze the morphologies and structures for materials of pristine and modified NCA. It is revealed that the co-coating layer plays a vital part in reducing the surface residual alkalis and improving the stability of NCA particles; as a result, the modified NCA exhibits a greatly improved rate capability, cycle performance, and low polarization impedance.

In Situ Surface Modification for Improving the Electrochemical Performance of Ni-Rich Cathode Materials by Using ZrP2 O7.

Ni-rich layered LiNi0.8 Mn0.1 Co0.1 O2 (NCM811) cathode material has promising prospects for high capacity batteries at acceptable cost. However, LiNi0.8 Mn0.1 Co0.1 O2 cathode material suffers from surface structure instability and capacity degradation upon cycling. In this study, in situ ZrP2 O7 coating is introduced to provide a protective structure. The optimum modification amount is 1.0 wt %. A series of characterization methods (X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy) verify the generation and structure of the coating layer. Electrochemical performance tests demonstrate that the cycle retention rate increases from 66.35 to 86.92 % after 100 cycles at 1 C rate. The dense inorganic pyrophosphate layer not only has chemical stability against the electrolyte but also eliminates surface residual lithium. The protective layer and the matrix are strongly joined by high-temperature heating, thereby giving a certain mechanical strength and protecting the overall structure of the topography. Therefore, the cycle and rate performance are enhanced by the modification with ZrP2 O7 .

Design and Synthesis of Double-Functional Polymer Composite Layer Coating To Enhance the Electrochemical Performance of the Ni-Rich Cathode at the Upper Cutoff Voltage.

Graphene has been implemented as a desirable additive to improve the electrochemical performance of Ni-rich cathode materials. However, it is not only hard to ensure the intimate interaction between them in practice, which may affect the surface electronic conductivity of the composite, but also a challenge to fabricate cathodes with uniform graphene coating because of its two-dimensional planar structure. Besides, the graphene coating layer is easily peeled off from the cathode material during the cycling process, especially at the upper cutoff voltage. Therefore, we introduced a double-functional layer synergistically modified strategy to facilitate the electrochemical properties of LiNi0.8Co0.1Mn0.1O2 cathode materials. In the designed architecture, the LiNi0.8Co0.1Mn0.1O2 particles were uniformly enwrapped by a functional reduced graphene oxide (RGO)-KH560 polymer composite layer which consists of an inner high-flexibility epoxy-functionalized silane (KH560) layer and an outer RGO layer with high electronic conductivity. The KH560 layer, in the structural system, is especially critical in connecting the layer of outer RGO and the inner surface of the active material, which brings about the perfect and complete double-functional coating layer and in turn fully expresses the modification effect of both KH560 and RGO in the improvement of electrochemical performance. Consequently, higher capacity retention, better rate, and improved high-temperature performances (55 °C) at the upper cutoff voltage (4.5 V) of this composite are identified when compared with the RGO-coated and pristine samples. In particular, the cathode with RGO (0.5%)-KH560 (0.5%) coating exhibits capacity retentions of 95.2 and 81.5% after 150 cycles at 1 C, 4.5 V at room and high temperatures, respectively.

Sodium Doping to Enhance Electrochemical Performance of Overlithiated Oxide Cathode Materials for Li-Ion Batteries via Li/Na Ion-Exchange Method.

Overlithiated oxide cathode materials show high capacity but poor cycle stability and voltage attenuation. In this work, a concentration difference driven molten salt ion exchange strategy is used to replace a small quantity of lithium ions by sodium ions. With the entry of sodium ions, the interplanar spacing is increased and the structure is stabilized. The electrochemical properties of materials have been improved obviously. The powder X-ray diffraction, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, and transmission electron microscopy are used to detect the entry of sodium ions and structural changes. The modified materials display high discharge specific capacity, excellent cycling performance, and reduced voltage attenuation.

Conductive Polymers Encapsulation To Enhance Electrochemical Performance of Ni-Rich Cathode Materials for Li-Ion Batteries.

Ni-rich cathode materials have drawn lots of attention owing to its high discharge specific capacity and low cost. Nevertheless, there are still some inherent problems that desiderate to be settled, such as cycling stability and rate properties as well as thermal stability. In this article, the conductive polymers that integrate the excellent electronic conductivity of polyaniline (PANI) and the high ionic conductivity of poly(ethylene glycol) (PEG) are designed for the surface modification of LiNi0.8Co0.1Mn0.1O2 cathode materials. Besides, the PANI-PEG polymers with elasticity and flexibility play a significant role in alleviating the volume contraction or expansion of the host materials during cycling. A diversity of characterization methods including scanning electron microscopy, energy-dispersive X-ray spectrometer, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared have demonstrated that LiNi0.8Co0.1Mn0.1O2 cathode materials is covered with a homogeneous and thorough PANI-PEG polymers. As a result, the surface-modified LiNi0.8Co0.1Mn0.1O2 delivers high discharge specific capacity, excellent rate properties, and outstanding cycling performance.

High-Conductive AZO Nanoparticles Decorated Ni-Rich Cathode Material with Enhanced Electrochemical Performance.

A facile solution route was employed for the preparation of an Al doped ZnO (AZO) coating layer, which was composed of many AZO nanoparticles. These nanoparticles have an average particle size of 50 nm and have been successfully decorated on the surface of NCM523. As cathode material for lithium ion batteries, the AZO-decorated NCM523 exhibits superior lithium storage improvements according to good cyclic performance, enhanced rate performance (134.2 mAhg-1 after 200 cycles at 10 C), and high-temperature performance (148.9 mAhg-1 at 10 C at 60 °C). Such significant improvement could be attributed to the structural superiority of the AZO decoration on the surface of NCM523, which would stabilize the surface structure of the bulk, suppress the undesirable side reaction at the interface of the electrodes, and lead to the enhancement of the conductivity. The preparation of AZO-decorated NCM523 provides an effective method for the high-performance lithium ion batteries and has a certain reference for other materials.

Enhancing the Thermal and Upper Voltage Performance of Ni-Rich Cathode Material by a Homogeneous and Facile Coating Method: Spray-Drying Coating with Nano-Al2O3.

The electrochemical performance of Ni-rich cathode material at high temperature (>50 °C) and upper voltage operation (>4.3 V) is a challenge for next-generation lithium-ion batteries (LIBs) because of the rapid capacity degradation over cycling. Here we report improved performance of LiNi0.8Co0.15Al0.05O2 materials via a LiAlO2 coating, which was prepared from a Ni0.80Co0.15Al0.05(OH)2 precursor by spray-drying coating with nano-Al2O3. Investigations by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy revealed that an Al2O3 layer is uniformly distributed on the precursor and a LiAlO2 layer on the as-prepared cathode material. Such a coating shell acts as a scavenger to protect the cathode material from attack by HF and serious side reactions, which remarkably enhances the cycle performance at 55 °C and upper operating voltage (4.4 and 4.5 V). In particular, the sample with a 2% Al2O3 coating shows capacity retentions of 90.40%, 85.14%, 87.85%, and 81.1% after 150 cycles at a rate of 1.0C at room temperature, 55 °C, 4.4 V, and 4.5 V, respectively, which are significantly higher than those of the pristine one. This is mainly due to the significant improvement of the structural stability led by the effective coating technique, which could be extended to other cathode materials to obtain LIBs with enhanced safety and excellent cycling stability.

Synthesis of the Micro-Spherical LiMn(2-x)Co(x)O4 as Cathode Material of Lithium Batteries.

Spherical Mn3O4 has been successfully synthesized by a controlled crystallization method. Then, micro-spherical particle of and LiMn(2-x)Co(x)O4 (X = 0, 0.01, 0.02, 0.03) were synthesized by using the as-prepared spherical Mn3O4Co3O4 and Li2CO3 as raw materials. The influences of Co doping on the structure, morphology and electrochemical performance were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and charge-discharge test. As a result, there is little difference between LiMn2O4 and Co-doped samples in structure and morphology. But Co doping has improved the cycle performance. LiMn1.97Co0.02O4 has an initial discharge specific capacity of 116.8 mA h/g at discharge current of 296 mA/g between 3 and 4.3 V, and retains 106.3 mA h/g after 350 cycles. The capacity retention at 55 degrees C is 91.52% after 100 cycles.

Syntheses of LiMn2O4 nanoparticles with nano-size precursor and its electrochemistry performance.

LiMn2O4 nanoparticles were prepared by solid state reaction with nano-size Mn3O4 precursor. Mn3O4 nanoparticles with the size of about 200 nm were prepared via controlled crystallization method, which were used as the precursor to prepare LiMn2O4 in nanometer size. The size of LiMn2O4 synthesized by the route is about 300 nm. Cyclic voltammetry shows two pairs of clearly-separated oxidation peaks, located at 4.07 and 4.19 V, and reduction peaks, located at 3.91 and 4.07 V. The as-synthesized LiMn2O4 nanoparticles exhibit good electrochemical performance with an initial discharge capacity of 125.9 mAh x g(-1) at a current density of 14.8 mA x g(-1). The LiMn2O4 nanoparticles show wonderful cycle ability and the capacity retention ratio is 92.1% after 650 cycles at the current density of 296 mA x g(-1).