锂离子电池正极材料Li(MnxFe1-x)PO4的合成及电化学性能的研究

采用高温固相法合成了组成为Li（MnxFe1-x）PO4（x=0、0．2、0．4、0．6、0．8、1．0）的锂离子电池正极材料。通过对合成样品的XRD、SEM及电化学性能（循环性能,大电流放电性能）的研究表明,少量Mn的掺杂未影响到LiFePO4的晶体结构,但显著改善了它的电化学性能。Li（Mn0.2Fe0.8）PO4与LiFePO4材料相比有更好的电化学性能,在低放电倍率（电流密度为20mA／g）时,放电容量为150mAh／g,当放电倍率提高到2C时,放电容量仍可达113mAh／g,且循环性能良好。     

High-Entropy Doping Boosts Ion/Electronic Transport of Na4Fe3(PO4)2(P2O7)/C Cathode for Superior Performance Sodium-Ion Batteries

Fe-based mixed phosphate cathodes for Na-ion batteries usually possess weak rate capacity and cycle stability challenges resulting from sluggish diffusion kinetics and poor conductivity under the relatively low preparation temperature. Here, the excellent sodium storage capability of this system is obtained by introducing the high-entropy doping to enhance the electronic and ionic conductivity. As designed high-entropy doping Na₄Fe_2.85(Ni,Co,Mn,Cu,Mg)_0.03(PO₄)₂P₂O₇ (NFPP-HE) cathode can release 122 mAh g⁻¹ at 0.1 C, even 85 mAh g⁻¹ at ultrahigh rate of 50 C, and keep a high retention of 82.3% after 1500 cycles at 10 C. Besides, the cathode also exhibits outstanding fast charge capacity in terms of the cyclability and capacity with 105 mAh g⁻¹ at 5 C/1 C, corresponding 94.3% retention after 500 cycles. The combination of in situ X-ray diffraction, density functional theory, conductive-atomic force microscopy, and galvanostatic intermittent titration technique tests reveal that the reversible structure evolution with optimized Na⁺ migration path and energy barrier boost the Na⁺ kinetics and improve the interfacial electronic transfer, thus improving performance.     

纳米结构的氧化钒作锂离子电池阴极材料的研究进展

V2O5具有独特的层状结构,适合于锂离子的存储,与传统的锰酸锂、钴酸锂、磷酸铁锂等阴极材料相比,表现出高的理论比容量和功率密度,作为锂离子电池阴极材料备受青睐。但它自身的结构不稳定、电导率低,导致实际比容量远低于理论值,且循环稳定性不能长期维持。正是由于这些制约因素,V2O5作锂离子电池阴极材料还有很大的研究价值。而利用各种制备方法将V2O5制备成具有各种纳米结构的材料,如一维的纳米线、纳米管等,二维的纳米片,三维的纳米空心球、纳米花等,改善材料固有的形貌结构,增大比表面积,增强锂离子在电极材料中的嵌入/脱出性能,提高储锂能力和比容量,同时通过掺杂改性等方法增强材料的导电性和循环稳定性,使V2O5作为锂离子电池阴极材料表现出优异的电化学性能成为可能。介绍了V2O5的晶体结构及其作为电极材料的纳米结构,以及不同的纳米结构对电极材料电化学性能的影响。     

Polyanion-Type Na3V2(PO4)2F3@rGO with High-Voltage and Ultralong-Life for Aqueous Zinc Ion Batteries

Aqueous zinc ion batteries (AZIBs) have attracted much interest in the next generation of energy storage devices because of their elevated safety and inexpensive price. Polyanionic materials have been considered as underlying cathodes owing to the high voltage, large ionic channels and fast ionic kinetics. However, the low electronic conductivity limits their cycling stability and rate performance. Herein, mesoporous Na₃V₂(PO₄)₂F₃ (N3VPF) nanocuboids with the size of 80–220 nm cladded by reduced graphene oxide (rGO) have been successfully prepared to form 3D composite (N3VPF@rGO) by a novel and fast microwave hydrothermal with subsequent calcination strategy. The enhanced conductivity, strengthened pseudocapacitive behaviors, enlarged D_Zn²⁺, and stable structure guarantee N3VPF@rGO with splendid Zn²⁺ storage performance, such as high capacity of 126.9 mAh g^-1 at 0.5 C (1 C = 128 mA g^-1), high redox potentials at 1.48/1.57 V, high rate capacity of 93.9 mAh g^-1 at 20 C (short charging time of 3 mins) and extreme cycling stability with capacity decay of 0.0074% per cycle after 5000 cycles at 15 C. The soft package batteries also present preeminent performance, demonstrating the practical application values. In situ X-ray diffraction, ex situ transmission electron microscopy and X-ray photoelectron spectroscopy reveal a reversible Zn²⁺ insertion/extraction mechanism.     

F掺杂 LiFePO4/C的固相合成及电化学性能

用廉价三价铁离子化合物为铁源,聚丙烯作还原剂和碳源,两步固相法合成F掺杂原位碳包覆LiFePO4正极材料.结果表明,合成产物具有完整的橄榄石型LiFePO4晶体结构,粉末形状近似球形,尺寸分布在50～200nm范围内,两步固相法更好地抑制了LiFePO4晶粒的长大.电化学测试结果表明,F掺杂提高了材料倍率放电性能,有效降低了材料电极的极化.在1C,2C,3C(C为150mA/g)充放电倍率下,LiFePO3.98F0.02/C的比容量分别为146mAh/g,137mAh/g,122mAh/g,1C循环55次后放电容量达到初始容量的99.3%.     

锂离子电池正极材料Li3V2（PO4）3存在的问题及改性研究进展

指出了Li3V2(PO4)3存在的主要问题及其改性办法,综述了包覆改性、掺杂改性以及控制样品的形貌和粒径3种改性手段近年来在Li3V2(PO4)3电化学改性上所取得的研究成果,评价了3种方式的优缺点,并展望了Li3V2(PO4)3今后的研究方向。     

磷酸锰铁锂正极材料的制备和性能

用球磨-热解法制备了锂离子电池碳包覆磷酸锰铁锂正极材料。通过XRD、TEM和电化学测试对材料进行了表征。所制备的材料平均粒径为100nm,碳在材料表面包覆均匀,包覆的碳层厚度约为2～3nm。在650℃下热解制备的LiMn0.5Fe0.5PO4正极材料具有最佳的电化学性能,其第一周的可逆容量为153.3mAh/g,经过50周的循环以后,可逆容量保持不变。材料在2.0C恒流放电时,放电容量仍然保持在121mAh/g左右,具有较优的倍率性能。     

Suppressing Surface Lattice Oxygen Release of Li‐Rich Cathode Materials via Heterostructured Spinel Li4Mn5O12 Coating

Lithium‐rich layered oxides with the capability to realize extraordinary capacity through anodic redox as well as classical cationic redox have spurred extensive attention. However, the oxygen‐involving process inevitably leads to instability of the oxygen framework and ultimately lattice oxygen release from the surface, which incurs capacity decline, voltage fading, and poor kinetics. Herein, it is identified that this predicament can be diminished by constructing a spinel Li₄Mn₅O₁₂ coating, which is inherently stable in the lattice framework to prevent oxygen release of the lithium‐rich layered oxides at the deep delithiated state. The controlled KMnO₄ oxidation strategy ensures uniform and integrated encapsulation of Li₄Mn₅O₁₂ with structural compatibility to the layered core. With this layer suppressing oxygen release, the related phase transformation and catalytic side reaction that preferentially start from the surface are consequently hindered, as evidenced by detailed structural evolution during Li⁺ extraction/insertion. The heterostructure cathode exhibits highly competitive energy‐storage properties including capacity retention of 83.1% after 300 cycles at 0.2 C, good voltage stability, and favorable kinetics. These results highlight the essentiality of oxygen framework stability and effectiveness of this spinel Li₄Mn₅O₁₂ coating strategy in stabilizing the surface of lithium‐rich layered oxides against lattice oxygen escaping for designing high‐performance cathode materials for high‐energy‐density lithium‐ion batteries.     

纳米LiFePO4/C复合正极材料的制备及其性能研究

采用碳热还原方法、以不同掺碳(葡萄糖为碳源)方式合成LiFePO4/C复合正极材料,利用X射线衍射仪、高倍率透射电镜以及电池测试仪等手段对样品进行了分析研究,并探讨了不同掺碳方式对复合LiFePO4/C正极材料性能的影响.结果表明,采用湿法加入葡萄糖制备的LiFePO4/C正极材料中LiFePO4的粒径范围在40～80nm左右,为纳米材料尺度,0.05C倍率下首次放电比容量达到160mAh/g,1C倍率下循环50次后,容量衰减仅为1.2%.     

Electrochemical Investigation of Calcium Substituted Monoclinic Li3V2(PO4)3 Negative Electrode Materials for Sodium- and Potassium-Ion Batteries

Herein, the electrochemical properties and reaction mechanism of Li_3‒2xCa_xV₂(PO₄)₃/C (x = 0, 0.5, 1, and 1.5) as negative electrode materials for sodium-ion/potassium-ion batteries (SIBs/PIBs) are investigated. All samples undergo a mixed contribution of diffusion-controlled and pseudocapacitive-type processes in SIBs and PIBs via Trasatti Differentiation Method, while the latter increases with Ca content increase. Among them, Li₃V₂(PO₄)₃/C exhibits the highest reversible capacity in SIBs and PIBs, while Ca_1.5V₂(PO₄)₃/C shows the best rate performance with a capacity retention of 46% at 20 C in SIBs and 47% at 10 C in PIBs. This study demonstrates that the specific capacity of this type of material in SIBs and PIBs does not increase with the Ca-content as previously observed in lithium-ion system, but the stability and performance at a high C-rate can be improved by replacing Li⁺ with Ca²⁺. This indicates that the insertion of different monovalent cations (Na⁺/K⁺) can strongly influence the redox reaction and structure evolution of the host materials, due to the larger ion size of Na⁺ and K⁺ and their different kinetic properties with respect to Li⁺. Furthermore, the working mechanism of both LVP/C and Ca_1.5V₂(PO₄)₃/C in SIBs are elucidated via in operando synchrotron diffraction and in operando X-ray absorption spectroscopy.     

Boosting High‐Rate Sodium Storage Performance of N‐Doped Carbon‐Encapsulated Na3V2(PO4)3 Nanoparticles Anchoring on Carbon Cloth

The further development of high‐power sodium‐ion batteries faces the severe challenge of achieving high‐rate cathode materials. Here, an integrated flexible electrode is constructed by smart combination of a conductive carbon cloth fiber skeleton and N‐doped carbon (NC) shell on Na₃V₂(PO₄)₃ (NVP) nanoparticles via a simple impregnation method. In addition to the great electronic conductivity and high flexibility of carbon cloth, the NC shell also promotes ion/electron transport in the electrode. The flexible NVP@NC electrode renders preeminent rate capacities (80.7 mAh g^?1 at 50 C for cathode; 48 mAh g^?1 at 30 C for anode) and superior cycle performance. A flexible symmetric NVP@NC//NVP@NC full cell is endowed with fairly excellent rate performance as well as good cycle stability. The results demonstrate a powerful polybasic strategy design for fabricating electrodes with optimal performance.