Spheres of Graphene and Carbon Nanotubes Embedding Silicon as Mechanically Resilient Anodes for Lithium-Ion Batteries
Jinhui XuQingyang YinXinru LiXinyi TanQian LiuLü XingBocheng CaoXintong YuanYuzhang LiLi ShenYunfeng Lu
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Abstract:
Novel anode materials for lithium-ion batteries were synthesized by in situ growth of spheres of graphene and carbon nanotubes (CNTs) around silicon particles. These composites possess high electrical conductivity and mechanical resiliency, which can sustain the high-pressure calendering process in industrial electrode fabrication, as well as the stress induced during charging and discharging of the electrodes. The resultant electrodes exhibit outstanding cycling durability (∼90% capacity retention at 2 A g-1 after 700 cycles or a capacity fading rate of 0.014% per cycle), calendering compatibility (sustain pressure over 100 MPa), and adequate volumetric capacity (1006 mAh cm-3), providing a novel design strategy toward better silicon anode materials.Keywords:
Calendering
Carbon fibers
Calendering plays a very important role in determining the final paper properties. In order to minimize the mechanical stress applied on paper and to acquire the desired paper properties, number of nips and nip pressure have been reduced recently.These techniques aim at reducing mechanical damages of paper, and obtaining smooth surfaces, as well as maintaining adequate physical properties of paper such as strength and dimensional stability.The hot calendering roll and the crown control roll have been developed to meet these requirements.This paper summarizes the past studies of calendering effects on paper properties, and introduces the research at PPRIC on hot calendering, and furthermore describes different kinds of hot calendering rolls and temperature-gradient calendering.Proper controls of basis weight and moisture profile in cross machine direction at the inlet of a calender are the prerequisites even in hot calendering and temperature gradient calendering.Lack of these conditions will lead to anisotropic expansion of paper.A method for calculating the magnitude of anisotropic expansion and its effect on nip pressure is presented.Appropriate choise of calendering method can minimize paper strength loss and can decrease the use of costly papermaking furnishes, which will bring us economic returns.
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This chapter contains sections titled: Objective and General Description of the Calendering Process History of Calendering The Different Calender Types The Main Calendering Methods for Various Paper and Board Grades References Further Reading
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In this study, the TG calendering technique was applied to multi-ply boxboard samples made from 100% recycled fibers. The effects of the following three calendering techniques on the surface properties and bulk of the board are investigated: conventional calendering, two-sided TG calendering, and one-sided TG calendering.
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Hanji is a traditional Korean handmade paper, which has been known in ancient Far East as excellent quality calligraphic paper for more than 1,500 year. Hanji is mostly made of Korean paper mulberry bast fibers, and if properly processed, normally lasts for more than 1,000 years with significant strength and still recognizable calligraphic writings or drawings on it. Dochim is a special way of Hanji calendering process, but is turned out to be quite different from modern calendering (machine calendering) in several aspects. In Dochim process, mechanical impacts were applied vertically to the surface of papers. Compared to the modern calendering, Dochim increased paper gloss much more, but paper smoothness a little less. By the Dochim process, densification occurred and the degree of densification was more sensitive to the fiber type in the Dochim process than in the calendering method.
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This chapter contains sections titled: Introduction Calendering Processes Applying Pressure in a Nip Heat Transfer in the Nip Effect of Calendering on Paper Structure and Surface Properties Conclusions and Trends in Calendering
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NIP
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Particle (ecology)
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본 연구에서는 리튬이차전지의 음극활물질로 graphite의 전기화학적 특성을 향상시키기 위하여 졸-겔 법에 의한 graphite/$SiO_2$ 복합소재를 제조하였다. 제조된 graphite/$SiO_2$ 합성물은 XRD, FE-SEM과 EDX를 사용하여 분석하였다. $SiO_2$ 에 의해 표면 개질된 graphite는 SEI 층을 안정화시키는데 장점을 보여 주었다. Graphite/$SiO_2$ 전극을 작업 전극으로, 리튬메탈을 상대전극으로 하여 리튬이차전지의 전기화학 특성을 조사하였다. $LiPF_6$ 염과 EC/DMC 용매를 전해질로 사용하여 제조한 코인 셀의 전기화학적 거동은 충방전, 사이클, 순환전압전류, 임피던스 테스트를 진행하여 평가하였다. Graphite/$SiO_2$ 전극을 사용한 리튬이차전지는 graphite 전극을 사용한 전지보다 우수한 특성을 보여주었으며, 0.1 C rate에서 465 mAh/g의 용량을 보여주었다. 또한 개질된 graphite 전극은 0.8 C rate에서 99%의 용량 보존율을 보여주었다. The graphite/$SiO_2$ composites as anode materials for lithium-ion batteries were prepared by sol-gel method to improve the graphite's electrochemical characteristics. The prepared graphite/$SiO_2$ composites were analysed by XRD, FE-SEM and EDX. The graphite surface modified by silicon dioxide showed several advantages to stabilize SEI layer. The electrochemical characteristics were investigated for lithium ion battery using graphite/$SiO_2$ as the working electrode and Li metal as the counter electrode. Electrochemical behaviors using organic electrolytes ($LiPF_6$ , EC/DMC) were characterized by charge/discharge, cycle, cyclic voltammetry and impedance tests. The lithium ion battery using graphite/$SiO_2$ electrodes had better capacity than that of using graphite electrodes and was able to deliver a discharge capacity with 475 mAh/g at a rate of 0.1 C. Also, the capacity retention ratio of the modified graphite reaches 99% at a rate of 0.8 C.
Lithium battery
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