Morphological solution for enhancement of electrochemical kinetic performance of LiFePO4

Piezoelectric polarization induced by dual piezoelectric materials ZnO nanosheets/MoS2 heterostructure for enhancing photoelectrochemical water splitting

Zinc oxide (ZnO) has a broad range of applications in piezo-photoelectrochemical water splitting. However, the narrow light absorption range and high photogenerated carrier recombination efficiency make ZnO somewhat limited in applying piezo-photoelectrochemical water splitting. Heterogeneous structure construction is a superior handle to these two drawbacks. Herein, few-layer molybdenum disulfide (MoS2) nanospheres are compounded on ZnO nanosheets (NSs) to form a dual-piezoelectric-material heterojunction of ZnO NSs/MoS2. The photocurrent density of ZnO NSs/MoS2 reaches 0.68 mA/cm2 at 1.23 V vs. RHE under ultrasonic vibrations. It is 2.4 times higher than that of ZnO NSs under ultrasonic vibrations. The efficient piezo-photoelectrochemical performance is attributed to increased absorption range and polarization field. On the one hand, the narrow band gap of the few-layer MoS2 widens the light absorption range of ZnO. On the other hand, compared to pure ZnO NSs, ZnO NSs/MoS2 has an enhanced polarization field under ultrasonic vibrations due to the piezoelectric properties of dual piezoelectric materials, which dramatically accelerates the electron transfer and suppresses the recombination of between electrons and holes. This work provides a new approach to constructing photoelectrodes with effective piezoelectric photocatalytic properties.

Enhancement of Li2ZrO3 Modification of the Cycle Life of N/S-Doped LiMn0.5Fe0.5PO4/C Composite Cathodes for Lithium Ion Batteries

LiMn_0.5Fe_0.5PO₄ cathodes have a high energy density but a poor rate and poor cycling performance. To this end, a series of N/S-doped LiMn_0.5Fe_0.5PO₄/C composite cathodes modified with different contents of Li₂ZrO₃ were prepared by a solvothermal synthesis combined with calcination. The microstructure, chemical composition, and electrochemical properties are analyzed. Li₂ZrO₃ adsorbed on the LiMn_0.5Fe_0.5PO₄ primary particles' surface in an amorphous state and on spherical particles (5-10 nm). The cycling life and rate performance of the cathodes are improved by the modification of a moderate amount of Li₂ZrO₃. The LMFP/NS-C/LZO1 shows available capacities of 166.8 and 118.9 mAh·g^-1 at 0.1 and 5 C, respectively. The LMFP/NS-C/LZO1 shows no capacity loss after 100 cycles of charging/discharging (1 C), and still has a high capacity retention of 92.0% after 1000 cycles of charging/discharging (5 C). The excellent cycling performance of the LMFP/NS-C/LZO1 can be attributed to the improvement of the cathode microstructure and the electrochemical kinetics and the inhibition of Mn²⁺ dissolution by the moderate Li₂ZrO₃ modification.

Facile synthesis of S-doped LiFePO4@N/S-doped carbon core-shell structured composites for lithium-ion batteries

Heteroatom-doped carbon can significantly improve the electrochemical performance of LiFePO₄cathodes, but it is limited by the complex preparation process and expensive dopants. A self-assembled S-doped LiFePO₄@N/S-doped C core-shell structured composites were synthesized by a convenient solvothermal method are reported. The structure and the electrochemical performance of the composites were characterized. In the S-doped LiFePO₄@N/S-doped C composites, the glucose-derived carbon microspheres were attached by LiFePO₄/C particles to form secondary particles in the core-shell structure. The thioacetamide regulated the morphology of LiFePO₄/C particles and provided N and S atoms to dope the composites. The S-doped LiFePO₄@N/S-doped C composites delivered specific discharge capacities of 157.81 mAh g^-1at 0.1 C and 121.26 mAh g^-1at 5 C, and capacity retention of 99.88% after 100 charge/discharge cycles. The excellent electrochemical performance of the S-doped LiFePO₄@N/S-doped C composites can be attributed to the synergism of thioacetamide and glucose.

One-Pot Synthesis of LiFePO4/N-Doped C Composite Cathodes for Li-ion Batteries

LiFePO4/N-doped C composites with core-shell structures were synthesized by a convenient solvothermal method. Cetyltrimethylammonium bromide (CTAB) and glucose were used as nitrogen and carbon sources, respectively. The growth of LiFePO4 nanocrystals was regulated by CTAB, resulting in an average particle size of 143 nm for the LiFePO4/N-doped C. The N atoms existed in the carbon of LiFePO4/N-doped C in the form of pyridinic N and graphitic N. The LiFePO4/N-doped C composites delivered discharge specific capacities of 160.7 mAh·g-1 (0.1 C), 128.4 mAh·g-1 (5 C), and 115.8 mAh·g-1 (10 C). Meanwhile, no capacity attenuation was found after 100 electrochemical cycles at 1 C. N-doping enhanced the capacity performance of the LiFePO4/C cathode, while the core-shell structure enhanced the cycle performance of the cathode. The electrochemical test data showed a synergistic effect between N-doping and core-shell structure on the enhancement of the electrochemical performance of the LiFePO4/C cathode.

Crystal alignment of a LiFePO4 cathode material for lithium ion batteries using its magnetic properties

We suggest a way to control the crystal orientation of LiFePO₄ using a magnetic field to obtain an advantageous structure for lithium ion conduction. We examined the magnetic properties of LiFePO₄ such as magnetism and magnetic susceptibility, which are closely related to the crystal rotation in an external magnetic field, and considered how to use these properties for desired crystal orientation; thus, we successfully fabricated the crystal-aligned LiFePO₄, in which the b-axis was highly aligned perpendicular to the surface of a current collector. Considering the low lithium ion conductivity of LiFePO₄ inherently originated from its one-dimensional path for lithium ion diffusion, the crystal-aligned LiFePO₄ potentially facilitates favorable transport kinetics for lithium ions during the charge/discharge process in lithium ion batteries. The crystal-aligned LiFePO₄ should afford lower electrode polarization than pristine LiFePO₄, and thus the former consistently exhibited higher reversible capacity than the latter.

The crystal orientation of LiFePO₄ was controlled by using a magnetic field to facilitate favorable transport kinetics for lithium ions.

High-tap density LiFePO4 microsphere developed by combined computational and experimental approaches

The lithiation/delithiation in LiFePO₄ is mainly anisotropic with lithium-ion diffusion being mainly limited to channels along the b-axis.

Solvothermal synthesis and self-assembling mechanism of micro-nano spherical LiFePO4 with high tap density

Well-defined three-dimensional porous LiFePO₄ microspheres composed of nanosheets with a high tap density of 1.4 g cm⁻³ were successfully synthesized by a simple one-step solvothermal method and their growth mechanism was also proposed.

Conformal Coating Strategy Comprising N-doped Carbon and Conventional Graphene for Achieving Ultrahigh Power and Cyclability of LiFePO4

Surface carbon coating to improve the inherent poor electrical conductivity of lithium iron phosphate (LiFePO4, LFP) has been considered as most efficient strategy. Here, we also report one of the conventional methods for LFP but exhibiting a specific capacity beyond the theoretical value, ultrahigh rate performance, and excellent long-term cyclability: the specific capacity is 171.9 mAh/g (70 μm-thick electrode with ∼10 mg/cm(2) loading mass) at 0.1 C (17 mA/g) and retains 143.7 mAh/g at 10 C (1.7 A/g) and 95.8% of initial capacity at 10 C after 1000 cycles. It was found that the interior conformal N-C coating enhances the intrinsic conductivity of LFP nanorods (LFP NR) and the exterior reduced graphene oxide coating acts as an electrically conducting secondary network to electrically connect the entire electrode. The great electron transport mutually promoted with shorten Li diffusion length on (010) facet exposed LFP NR represents the highest specific capacity value recorded to date at 10 C and ultralong-term cyclability. This conformal carbon coating approach can be a promising strategy for the commercialization of LFP cathode in lithium ion batteries.

Synthesis, characterisation and enhanced electrochemical performance of nanostructured Na2FePO4F for sodium batteries

Nanostructured Na₂FePO₄F was synthesised by a soft template method, followed by high-energy ball milling (HEBM) and post-heat treatment. The HEBM sample shows excellent sodium storage performance with a discharge capacity of 116 mA h g⁻¹at 0.1 C.

Novel synthesis of Mn3(PO4)2·3H2O nanoplate as a precursor to fabricate high performance LiMnPO4/C composite for lithium-ion batteries

Mn₃(PO₄)₂·3H₂O precursor was synthesized by a novel precipitation process using ethanol as initiator, and was lithiated to LiMnPO₄/C composite via a combination of wet ball-milling and heat treatment.

Enhancing the electrochemical kinetics of high voltage olivine LiMnPO4 by isovalent co-doping

We report here doping of Fe(2+) and/or Mg(2+) in LiMnPO4 cathode material to enhance its lithium storage performance and appraise the effect of doping. For this purpose, LiMn0.9Fe(0.1-x)MgxPO4/C (x = 0 and 0.05) and LiMn0.95Mg0.05PO4/C have been prepared by a ball mill assisted soft template method. These materials were prepared with similar morphology, particle size and carbon content. Amongst them, the isovalent co-doped LiMn0.9Fe0.05Mg0.05PO4/C sample shows better electrochemical performance compared to LiMn0.9Fe0.1PO4/C and LiMn0.95Mg0.05PO4/C samples. For instance, a lithium storage capacity of 159 mA h g(-1) is obtained at 0.1 C for LiMn0.9Fe0.05Mg0.05PO4/C material with a relatively low polarization of ~139 mV. This is in sharp contrast to LiMn0.9Fe0.1PO4/C and LiMn0.95Mg0.05PO4/C which show only 136.8 and 128.4 mA h g(-1) at 0.1 C with the polarization of ~222 and 334 mV respectively. Further, the LiMn0.9Fe0.05Mg0.05PO4/C electrode delivers discharge capacities of 155.8, 141.4, 118.8, 104.6, 81.4 and 51.8 mA h g(-1) at 0.2, 0.5, 1, 2, 5 and 10 C respectively. This electrode material also retains a capacity of 116 mA h g(-1) at 1 C after 200 cycles, which is 96% of its initial capacity. Such improved cycling stability of LiMn0.9Fe0.05Mg0.05PO4/C is attributed to the suppressed Mn dissolution in the electrolyte compared to the other samples. Further, during the Li extraction process, delithiated phases created from the Fe(2+)/Fe(3+) redox reaction (~3.45 V) favor enhanced electrochemical activity of the succeeding Mn(2+)/Mn(3+) redox couples. The fully charged state (4.6 V) contains a partially lithiated phase owing to the presence of electrochemically inactive Mg(2+). The presence of such lithiated phase provides a favourable environment for the subsequent lithium insertion process. We also observe improved electronic conductivity and Li-ion diffusion for the co-doped sample compared to LiMnPO4 doped with either Fe(2+) or Mg(2+) by impedance measurements. The improved storage performance of co-doped LiMnPO4 is thus explained in terms of (i) favorable extraction and insertion reactions and (ii) enhanced transport properties.

Crystal orientation tuning of LiFePO4 nanoplates for high rate lithium battery cathode materials

We report the crystal orientation tuning of LiFePO(4) nanoplates for high rate lithium battery cathode materials. Olivine LiFePO(4) nanoplates can be easily prepared by glycol-based solvothermal process, and the largest crystallographic facet of the LiFePO(4) nanoplates, as well as so-caused electrochemical performances, can be tuned by the mixing procedure of starting materials. LiFePO(4) nanoplates with crystal orientation along the ac facet and bc facet present similar reversible capacities of around 160 mAh g(-1) at 0.1, 0.5, and 1 C-rates but quite different ones at high C-rates. The former delivers 156 mAh g(-1) and 148 mAh g(-1) at 5 C-rate and 10 C-rate, respectively, while the latter delivers 132 mAh g(-1) and only 28 mAh g(-1) at 5 C-rate and 10 C-rate, respectively, demonstrating that the crystal orientation plays important role for the performance of LiFePO(4) nanoplates. This paves a facile way to prepare high performance LiFePO(4) nanoplate cathode material for lithium ion batteries.