Facile synthesis of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> microsheets with porous micro-nanostructure as high-rate cathode materials for Li-ion batteries

Porous LiMn₂O₄ microsheets with micro-nanostructure have been successfully prepared through a simple carbon gel-combustion process with a microporous membrane as hard template. The crystal structure, morphology, chemical composition, and surface analysis of the as-obtained LiMn₂O₄ microsheets are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscope (XPS). It can be found that the as-prepared LiMn₂O₄ sample presents the two-dimensional (2-D) sheet structure with porous structure comprised with nano-scaled particles. As cathode materials for lithium-ion batteries, the obtained LiMn₂O₄ microsheets show superior rate capacities and cycling performance at various charge/discharge rates. The LiMn₂O₄ microsheets exhibit a higher charge and discharge capacity of 137.0 and 134.7 mAh g^?1 in the first cycle at 0.5 C, and it remains 127.6 mAh g^?1 after 50 cycles, which accounts for 94.7% discharge capacity retention. Even at 10 C rate, the electrode also delivers the discharge capacity of 91.0 mAh g^?1 after 300 cycles (93.5% capacity retention). The superior electrochemical properties of the LiMn₂O₄ microsheets could be attributed to the unique microsheets with porous micro-nanostructure, more active sites of the Li-ions insertion/deinsertion for the higher contact area between the LiMn₂O₄ nano-scaled particles and the electrolyte, and better kinetic properties, suggesting the applications of the sample in high-power lithium-ion batteries.     

Morphology-controllable synthesis of LiMn2O4 particles as cathode materials of lithium batteries

We reported a new method for the preparation of morphology-controllable LiMn₂O₄ particles. In this method, dimension-different MnO₂ nanowires synthesized hydrothermally by adjusting the reaction temperature were used as the precursor. The morphology and structure of the resulting products were characterized with scanning electron microscope and X-ray diffraction, and the performances of the prepared LiMn₂O₄ samples as cathode material of lithium batteries were investigated by cyclic voltammetry and galvanostatic charge/discharge test. The results indicate that the morphology of LiMn₂O₄ transforms from tridimensional particle (TP) to unidimensional rod (UR) through quadrate lamina (QL) with increasing the diameter and length of MnO₂ nanowires. Although the cyclic stabilities of LiMn₂O₄-TP, LiMn₂O₄-QL, and LiMn₂O₄-UR are very close (the 0.1 C capacity after 50 cycles is 101, 93, and 99 mAh g^?1 at 25 °C, and 84, 78, and 82 mAh g^?1 at 50 °C, respectively), LiMn₂O₄-QL delivers much higher rate capacity (about 70 mAh g^?1 at 5 C and 30 mAh g^?1 at 10 C) than LiMn₂O₄-TP and LiMn₂O₄-UR (about 20 mAh g^?1 at 5 C, 3 mAh g^?1 at 10 C, 25 mAh g^?1 at 5 C, and 3 mAh g^?1 at 10 C).     

Synthesis and electrochemical characterization of duo doped spinels (zinc and praseodymium) for use in lithium rechargeable batteries

LiMn₂O₄ and LiZn_xPr_yMn_2?x?yO₄ (x = 0.10–0.24; y = 0.01–0.10) powders have been synthesized by sol–gel method using palmitic acid as chelating agent. The synthesized samples have been subjected to thermo gravimetric and differential thermal analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX). The sol–gel route bestows low calcination temperature, shorter heating time, high purity, good control over stoichiometry, small particle size, high surface area, good surface morphology and better homogeneity, The XRD patterns reveal high degree of crystallinity and better phase purity. SEM and TEM images exhibit nano-sized nature particles with good agglomeration. EDAX peaks of Zn, Pr, Mn and O have been confirmed in actual compositions of LiMn₂O₄ and LiZn_xPr_yMn_2?x?yO₄. Charge–discharge studies of pristine spinel LiMn₂O₄ heated at 850 °C delivers discharge capacity of 132 mA h g^?1 corresponding to columbic efficiency of 73 % during the first cycle. At the end of 10th cycles, it delivers maximum discharge capacity of 112 mA h g^?1 with columbic efficiency of 70 % and capacity fade of 0.15 mA h g^?1 cycle^?1 over the investigated 10 cycles. Inter alia, all dopants concentrations, LiZn_0.10Pr_0.10Mn_1.80O₄ exhibits the better cycling performance (1st cycle discharge capacity: 130 mA h g^?1 comparing to undoped spinel 132 mA h g^?1) corresponding to columbic efficiency of 73 % with capacity fade of 0.12 mA h g^?1 cycle^?1.     

Polymer template-assisted microemulsion synthesis of large surface area, porous Li2MnO3 and its characterization as a positive electrode material of Li-ion cells

Lithium-rich manganese oxide (Li₂MnO₃) is prepared by reverse microemulsion method employing Pluronic acid (P123) as a soft template and studied as a positive electrode material. The as-prepared sample possesses good crystalline structure with a broadly distributed mesoporosity but low surface area. As expected, cyclic voltammetry and charge–discharge data indicate poor electrochemical activity. However, the sample gains surface area with narrowly distributed mesoporosity and also electrochemical activity after treating in 4 M H₂SO₄. A discharge capacity of about 160 mAh g^?1 is obtained. When the acid-treated sample is heated at 300 °C, the resulting porous sample with a large surface area and dual porosity provides a discharge capacity of 240 mAh g^?1. The rate capability study suggests that the sample provides about 150 mAh g^?1 at a specific discharge current of 1.25 A g^?1. Although the cycling stability is poor, the high rate capability is attributed to porous nature of the material.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/rice husk-based maco-/mesoporous carbon bone nanocomposite as superior high-rate anode for lithium ion battery

Rice husks (RHs), a kind of biowastes, are firstly hydrothermally pretreated by HCl aqueous solution to achieve promising macropores, facilitating subsequently impregnating ferric nitrate and urea aqueous solution, the precursor of Fe₃O₄ nanoparticles. A Fe₃O₄/rice husk-based maco-/mesoporous carbon bone nanocomposite is finally prepared by the high-temperature hydrothermal treatment of the precursor-impregnated pretreated RHs at 600 °C followed by NaOH aqueous solution treatment for dissolving silica and producing mesopores. The macro-/mesopores are able to provide rapid lithium ion-transferring channels and accommodate the volumetric changes of Fe₃O₄ nanoparticles during cycling as well. Besides, the macro-/mesoporous carbon bone can offer rapid electron-transferring channels through directly fluxing electrons between Fe₃O₄ nanoparticles and carbon bone. As a result, this nanocomposite delivers a high initial reversible capacity of 918 mAh g^?1 at 0.2 A g^?1 and a reversible capacity of 681 mAh g^?1 remained after 200 cycles at 1.0 A g^?1. The reversible capacities at high current densities of 5.0 and 10.0 A g^?1 still remain at high values of 463 and 221 mAh g^?1, respectively.     

BiFeO<Subscript>3</Subscript>-coated spinel LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> with improved electrochemical performance as cathode materials for lithium-ion batteries

Spinel LiNi_0.5Mn_1.5O₄ cathode material is a promising candidate for next-generation rechargeable lithium-ion batteries. In this work, BiFeO₃-coated LiNi_0.5Mn_1.5O₄ materials were prepared via a wet chemical method and the structure, morphology, and electrochemical performance of the materials were studied. The coating of BiFeO₃ has no significant impact on the crystal structure of LiNi_0.5Mn_1.5O₄. All BiFeO₃-coated LiNi_0.5Mn_1.5O₄ materials exhibit cubic spinel structure with space group of Fd3m. Thin BiFeO₃ layers were successfully coated on the surface of LiNi_0.5Mn_1.5O₄ particles. The coating of 1.0 wt% BiFeO₃ on the surface of LiNi_0.5Mn_1.5O₄ exhibits a considerable enhancement in specific capacity, cyclic stability, and rate performance. The initial discharge capacity of 118.5 mAh g^?1 is obtained for 1.0 wt% BiFeO₃-coated LiNi_0.5Mn_1.5O₄ with very high capacity retention of 89.11% at 0.1 C after 100 cycles. Meanwhile, 1.0 wt% BiFeO₃-coated LiNi_0.5Mn_1.5O₄ electrode shows excellent rate performance with discharge capacities of 117.5, 110.2, 85.8, and 74.8 mAh g^?1 at 1, 2, 5, and 10 C, respectively, which is higher than that of LiNi_0.5Mn_1.5O₄ (97.3, 90, 77.5, and 60.9 mAh g^?1, respectively). The surface coating of BiFeO₃ effectively decreases charge transfer resistance and inhibits side reactions between active materials and electrolyte and thus induces the improved electrochemical performance of LiNi_0.5Mn_1.5O₄ materials.     

A facile bubble-assisted synthesis of porous Zn ferrite hollow microsphere and their excellent performance as an anode in lithium ion battery

Pure porous hollow Zn ferrite (ZnFe₂O₄) microspheres have been successfully synthesized by a facile bubble assisted method in the presence of ammonium acetate (NH₄Ac) as an anode material in lithium ion battery. The shape, size, and morphology of Zn ferrite are investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Furthermore, the probable bubble-assisted formation mechanism of porous hollow Zn ferrite spheres based on the experimental results is proposed. With the porous hollow structure, the obtained pure Zn ferrite particle as an anode in lithium ion battery demonstrates high capacity and excellent cycle ability. The high initial discharge specific capacity is approximately 1,400 mAh g^?1 and a reversible specific capacity approaches 584 mAh g^?1 after 100 cycles at a constant current density of 100 mA g^?1. The excellent electrochemical performance of the as-prepared Zn ferrite could be attributed to the special structure with which the volume expansion and pulverization of the particles became increasingly reduced.     

The electrochemical properties of Fe- and Ni-cosubstituted Li2MnO3 via combustion method

The Co-free Li_1.20Mn_0.54Ni _x Fe _y O₂ (x/y?=?0.5, 1.0, 2.0) materials were synthesized by combustion method. The effects of the preparation condition on the structure, morphology, and electrochemical performance were investigated by X-ray diffractometry, scanning electron microscopy, charge–discharge tests, and cyclic voltammetry (CV). The results indicate that the structure and electrochemical characteristics are sensitive to the preparation condition when a large amount of Fe is included. A pure layered α-NaFeO₂ structure with R-3m space group and the discharge capacities of over 200 mAh g^?1 were observed in some as-prepared cathode materials. Particularly, the Li_1.2Mn_0.54Ni_0.13Fe_0.13O₂ prepared by mixing an excess amount of lithium and by firing at 600 °C exhibits a second discharge capacity of 264 mAh g^?1 in the voltage range of 1.5–4.8 V under current density of 30 mA g^?1 at 30 °C and discharge capacity of 223 mAh g^?1 at 2.0–4.8 V. Nevertheless, an unpleasant capacity fading was observed and is primarily ascribed to transformation from a rock-layered structure into a spinel one according to CV testing.     

石墨烯/尖晶石LiMn2O4纳米复合材料制备及电化学性能

采用溶胶凝胶法和还原氧化石墨法制备尖晶石LiMn2O4纳米晶和石墨烯纳米片,并采用冷冻干燥法制备了石墨烯/尖晶石LiMn2O4纳米复合材料,利用XRD、SEM、AFM等对其结构及表面形貌进行表征;利用CV、充放电、EIS研究纳米复合材料的电化学性能和电极过程动力学特征。结果表明:纳米LiMn2O4电极材料及其石墨烯掺杂纳米复合材料的放电比容量分别为107.16 mAh.g-1,124.30 mAh.g-1,循环100周后,对应容量保持率为74.31%和96.66%,石墨烯可显著改善尖晶石LiMn2O4电极材料的电化学性能,归结于其良好的导电性。纳米复合材料EIS上感抗的产生与半导体尖晶石LiMn2O4不均匀地分布在石墨烯膜表面所造成局域浓差有关,并提出了感抗产生的模型。     

Influence of annealing temperature on microstructural and electrochemical properties of rf-sputtered LiMn2O4 film cathodes

The microstructural and electrochemical properties of rf-sputtered LiMn₂O₄ films were investigated as a function of post-deposition process. The degree of crystallization in the films gradually increased with the increase of annealing temperature (T _a). The films annealed at T _a?=?973 K exhibited characteristic peaks with predominant (111) orientation representing the cubic spinel structure of Fd3m symmetry. The estimated Mn–Mn and Mn–O distances obtained from the X-ray diffraction data were observed to be increased slightly with T _a. Characteristic changes in surface morphological features were observed as a function of T _a as evidenced from scanning electron microscopy. The estimated root mean square (RMS) roughness of the films increased from 97 to 161 nm with augmentation of T _a. The electrochemical studies, viz. cyclic voltammetry (CV), specific discharge capacity and Li ion diffusion coefficient were carried out for annealed LiMn₂O₄ films in saturated aqueous electrolyte (Li₂SO₄) in the potential window of 0–1.2 V and correlated with surface morphology and grain size. The LiMn₂O₄ films annealed at T _a?=?973 K exhibited better electrochemical performance and demonstrated a discharge capacity of about 53.5 μA h cm^?2 μm^?1 with diffusion coefficient of 1.2?×?10^?13 cm² s^?1.     

Synthesis of high-energy-density LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode through surficial Nb doping for lithium-ion batteries

LiMn₂O₄ is one of the most promising cathode materials due to its high abundance and low cost. However, the practical application of LiMn₂O₄ is greatly limited owing to its low volumetric energy density. Therefore, increasing its energy density is an urgent problem to be resolved. Herein, using the simple and mass production preferred solid-state reaction, surficial Nb-doped LiMn₂O₄ composed of the truncated octahedral or spherical-like primary particles are successfully synthesized. Auger electron spectroscopy (AES) and X-ray diffraction (XRD) characterizations confirm that most of Nb⁵⁺ enrich in the surficial layer of the particles to form a LiMn_2-xNb_xO₄ phase. This kind of doping can increase the specific discharge capacity of LiMn₂O₄ materials. Contrast with the pristine LiMn₂O₄, the discharge capacity of LiMn_1.99Nb_0.01O₄-based 18650R-type battery increases from 1497 to 1705 mAh with the volumetric energy density increasing by ~?13.9%, benefiting from the joint increments of the specific discharge capacity from 119.5 to 123.7 mAh g^?1 and the compacted density from 2.81 to 3.10 g cm^?3. Furthermore, the capacity retention after 500 cycles at 1 C (1500 mA) is also improved by 17.1%.

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Nearly monodispersed LiFePO<Subscript>4</Subscript>F nanospheres as cathode material for lithium ion batteries

Tavorite-structured lithium transition metal fluorophosphates have been considered as a good alternative to olivine-type cathode for lithium-ion batteries due to its exceptional ionic conductivity and excellent thermal stability. In this work, nearly monodisperse LiFePO₄F nanospheres with high purity are successfully synthesized by a solid-state route associated with chemically induced precipitation method for the first time. The synthesized LiFePO₄F presents nearly monodisperse nanospheres particles with average particle size of ~?500 nm. Cyclic voltammetry data exhibit a clear indication of the Fe³⁺/Fe²⁺ redox couple that involves a two-phase transition. Its electrochemical behaviors are examined by galvanostatic charge-discharge. The results show that the initial discharge capacity is 110.2 mAh g^?1 at 0.5 C, after 200 cycles is still retained 104.0 mAh g^?1 with the retention rate of 94.4%. The excellent cycle performance is mainly attributed to the uniform nanospheres-like morphology which is not only beneficial to shorten the transport distance of ions and electrons, but also improve the interface area between electrode and electrolyte, and thus improve the kinetics of Li ions.     

Metal-free boron-doped carbon microspheres as excellent cathode catalyst for rechargeable Li–O<Subscript>2</Subscript> battery

Rechargeable Li–O₂ batteries are attracting more and more interest due to their high energy density. Meanwhile, the replacement of high-cost and scarce precious-metal catalysts has attracted more and more attention. Currently, many academic researchers have paid attention to find highly efficient metal-free catalysts as air cathode material. Herein, the boron-doped carbon microspheres (B-CMs) were prepared through a novel and facile static calcination method and showed high electrocatalytic activity as a cathode material. The battery with a B-CM cathode delivered a high initial discharge capacity of 13,757.2 mAh g^?1 and outstanding coulombic efficiency of 90.1 % at 100 mA g^?1. In addition, stable cyclability (151 cycles with stable discharge voltage of ~2.60 V with a cutoff capacity of 1000 mAh g^?1 at 200 mA g^?1) has been exhibited. These performances are due to three main points: boron carbide compound changed the surface area of the CMs and formed the mesopore architectures as well as the large surface area of 683.738 m² g^?1; the reduce of boron atom can slow down the oxidation of the CMs during the cyclings; and finally, the electron-deficient boron atom introduction greatly facilitated Li⁺ diffusion and electrolyte immersion and enhanced the oxygen reduction and evolution reaction kinetics.     

Amorphous iron phosphate/carbonized polyaniline nanorods composite as cathode material in sodium-ion batteries

As-prepared polyaniline (PANI) nanorods have been used to synthesize an iron phosphate/polyaniline (FePO₄/PANI) composition through the microemulsion technique. After sintering at 460 °C under a nitrogen protective atmosphere, the PANI carbonized, yielding the amorphous iron phosphate/carbonized polyaniline nanorods (FePO₄/CPNRs) composite, which acts as the cathode material in sodium-ion batteries (SIBs). The electrochemical performance of FePO₄/CPNRs composite shows an initial discharge specific capacity of 140.2 mAh g^?1, with the discharge specific capacity being maintained at 134.4 mAh g^?1 after the 120th cycle, up to 87.9 % of the theoretical capacity (154.1 mAh g^?1 for NaFePO₄), as well as an excellent rate capability in sodium-ion batteries. Compared with pure FePO₄, the electrochemical performance has been greatly improved. On the one hand, using the CPNRs as conductive medium significantly improves electronic transport. On the other hand, the FePO₄ sphere of nanoscale particles, which has a large specific surface area, can promote an active material/electrolyte interface reaction and improve the speed of sodiation and desodiation during the charge and discharge process. The amorphous FePO₄/CPNRs composite shows outstanding electrochemical performance as competitive cathode material in SIBs.     

Green fabrication of sandwich-like and dodecahedral C@Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@C as high-performance anode for lithium-ion batteries

Sandwich-structured C@Fe₃O₄@C hybrids with Fe₃O₄ nanoparticles sandwiched between two conductive carbon layers have attracted more and more attention owing to enhanced synergistic effects for lithium-ion storage. In this work, an environment-friendly procedure is developed for the fabrication of sandwich-like C@Fe₃O₄@C dodecahedrons. Zeolitic imidazolate framework (ZIF-8)-derived carbon dodecahedrons (ZIF-C) are used as the carbon matrix, on which iron precursors are homogeneously grown with the assistance of a polyelectrolyte layer. The subsequent polydopamine (PDA) coating and calcination give rise to the formation of sandwiched ZIF-C@Fe₃O₄@C. When being evaluated as the anode material for lithium-ion batteries, the obtained hybrid manifests a high reversible capacity (1194 mAh g^?1 at 0.05 A g^?1), good high-rate behavior (796 mAh g^?1 at 10 A g^?1), and negligible capacity loss after 120 cycles.     

Rational design of double-confined Mn<Subscript>2</Subscript>O<Subscript>3</Subscript>/S@Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocube cathodes for lithium-sulfur batteries

Due to the high specific capacities and environmental benignity, lithium-sulfur (Li-S) batteries have shown fascinating potential to replace the currently dominant Li-ion batteries to power portable electronics and electric vehicles. However, the shuttling effect caused by the dissolution of polysulfides seriously degrades their electrochemical performance. In this paper, Mn₂O₃ microcubes are fabricated to serve as the sulfur host, on top of which Al₂O₃ layers of 2 nm in thickness are deposited via atomic layer deposition (ALD) to form Mn₂O₃/S (MOS) @Al₂O₃ composite electrodes. The MOS@Al₂O₃ electrode delivers an excellent initial capacity of 1012.1 mAh g^?1 and a capacity retention of 78.6% after 200 cycles at 0.5 C, and its coulombic efficiency reaches nearly 99%, giving rise to much better performance than the neat MOS electrode. These findings demonstrate the double confinement effect of the composite electrode in that both the porous Mn₂O₃ structure and the atomic Al₂O₃ layer serve as the spacious host and the protection layer of sulfur active materials, respectively, for significantly improved electrochemical performance of the Li-S battery.     

SnO2 sheet/graphite composite as anode material with improved electrochemical performance for lithium-ion batteries

The SnO₂ sheet/graphite composite was synthesized by a hydrothermal method for high-capacity lithium storage. The microstructures of products were characterized by XRD and FE-SEM. The electrochemical performance of SnO₂ sheet/graphite composite was measured by galvanostatic charge/discharge cycling and EIS. The first discharge and charge capacities are 1,072 and 735 mAh g^?1 with coulombic efficiency of 68.6 %. After 40 cycles, the reversible discharge capacity is still maintained at 477 mAh g^?1. The results show that the SnO₂ sheet/graphite composite displays superior Li-battery performance with large reversible capacity and good cyclic performance.     

Nanofibers of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/C@MWCNTs as the cathode material for lithium-ion batteries

Vanadium pentoxide (V₂O₅) nanofibers (NFs) with a thin carbon layer of 3–5 nm, which wrapped on V₂O₅ nanoparticles, and integrated multiwalled carbon nanotubes (MWCNTs) have been fabricated via simple electrospinning followed by carbonization process and post-sintering treatment. The obtained composite displays a NF structure with V₂O₅ nanoparticles connected to each other, and good electrochemical performance: delivering initial capacity of 320 mAh g^?1 (between 2.0 and 4.0 V vs. Li/Li⁺), good cycling stability (223 mAh g^?1 after 50 cycles), and good rate performance (~?150 mAh g^?1 at 2 A g^?1). This can attribute to the carbon wrapped on the V₂O₅ nanoparticles which can not only enhance the electric conductivity to decrease the impendence of the cathode materials but also maintain the structural stability to protect the nanostructure from the corruption of electrolyte and the strain stress due to the Li-ion intercalation/deintercalation during the charge/discharge process. And, the added MWCNTs play the role of framework of the unique V₂O₅ coated by carbon layer and composited with MWCNT NFs (V₂O₅/C@MWCNT NFs) to ensure the material is more stable.     

Interlayer-expanded MoS<Subscript>2</Subscript>/graphene composites as anode materials for high-performance lithium-ion batteries

A facile strategy was developed to prepare interlayer-expanded MoS₂/graphene composites through a one-step hydrothermal reaction method. MoS₂ nanosheets with several-layer thickness were observed to uniformly grow on the surface of graphene sheets. And the interlayer spacing of MoS₂ in the composites was determined to expand to 0.95 nm by ammonium ions intercalation. The MoS₂/graphene composites show excellent lithium storage performance as anode materials for Li-ion batteries. Through gathering advantages including expanded interlayers, several-layer thickness, and composited graphene, the composites exhibit reversible capacity of 1030.6 mAh g^?1 at the current density of 100 mA g^?1 and still retain a high specific capacity of 725.7 mAh g^?1 at a higher current density of 1000 mA g^?1 after 50 cycles.     

Lead sulfate used as the positive active material of lead acid batteries

Lead sulfate is produced when a lead acid battery discharges, and it is also known that big PbSO₄ crystals are less active than the smaller ones because they dissolve slower, thus result in failure of the battery. However, little is known if chemically prepared PbSO₄ can be used as active material of lead acid batteries. Here, we report the preparation of PbSO₄ by facile chemical precipitation of aqueous lead acetate with sodium sulfate and its utilization as the positive active material. The results show that the PbSO₄ alone is not good enough for the purpose, but its mixtures with Pb₃O₄ are as excellent as the industrial leady oxide. For example, the mixtures containing 5, 10, 20, and 30 wt.% of Pb₃O₄ discharge 78.2, 92.9, 88.0, and 91.5 mAh g^?1 at a current density of 100 mA g^?1, respectively. Also, the one with 10 % Pb₃O₄ remains 93 % capacity in 150, 100 % DOD cycles.