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C: Energy Conversion and Storage; Energy and Charge Transport

Rational Design of Core-Shell-Structured Particles by a One-Step and Template-Free Process for High-Performance Lithium/Sodium Ion Batteries Huajun Tian, Yujia Liang, Joseph Repac, Shunlong Zhang, Chao Luo, Sz-Chian Liou, Guoxiu Wang, Sheryl H. Ehrman, and Wei-Qiang Han J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b05452 • Publication Date (Web): 05 Sep 2018 Downloaded from http://pubs.acs.org on September 5, 2018

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The Journal of Physical Chemistry

Rational Design of Core-Shell-Structured Particles by a One-Step and Template-Free Process for High-Performance Lithium/Sodium Ion Batteries Huajun Tian†⊥, Yujia Liang‡⊥, Joseph Repac‡, Shunlong Zhang§, Chao Luo‡, SzChian Liou∆, Guoxiu Wang†, Sheryl H. Ehrman‡,||*and Weiqiang Han§,∇*

†

Centre for Clean Energy Technology, Faculty of Science, University of Technology Sydney,

NSW 2007, Australia. ‡

Department of Chemical and Biomolecular Engineering, University of Maryland, College Park,

Maryland 20742, USA §

Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences,

Ningbo 315201, China ∆

AIM Lab, NanoCenter, University of Maryland, College Park, MD 20742, USA

||

Charles W. Davidson College of Engineering, San Jose State University, San Jose, California,

95192, USA ∇

School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China

*

Corresponding authors: [email protected]; [email protected]

⊥These authors contributed equally.

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Abstract Tin (Sn)-based materials are one of most promising candidates for rechargeable (Li+ and Na+ ion) batteries because of their high theoretical capacities (993 mAh/g for Li4.4Sn and 847 mAh/g for Na15Sn4) and reasonable working potentials. However, Sn-based anodes suffer from huge volume changes during cycling that hinder the applications in commercialized rechargeable batteries. Unique particle engineering to fabricate Sncore-Carbonshell (Sn@C) particles has been shown to address or circumvent these problems. In this work, a distinct core-shell structured Sn@C anode material has been successfully developed by using a one-step and template-free process (colloidal spray pyrolysis (CSP)). A comprehensive analysis of chemical reaction kinetics of core-shell particles assists the product design to control the particle composition and structure by tuning the process variables such as reaction temperature and cosolvent concentration. The unique Sn@C anode delivers a high capacity of 720 mAh/g after 300 cycles at 0.5C for lithium-ion batteries and a high capacity of > 500 mAh/g at 0.2C for sodium-ion batteries. More importantly, this work advances the design of high-performance Sn@C composites for lithium/sodium-ion batteries in scalable process development, particle engineering, and material innovation.


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Introduction High-performance rechargeable batteries (e.g., Li/Na1-2, Mg3,4, Al5, and K-ion6 batteries) have attracted much attention due to the increasing demands of electric vehicle and mobile/stationary applications, which require high-energy-density/power cells with long-term cycle life and high safety reliability. In the past decades, graphite, one of the most practical anode materials for lithium ion batteries (LIBs), has been improved through physical and chemical modifications to reach its theoretical capacity (372 mAh/g). However, its inherent low capacity is an obstacle for the further applications of LIBs in high-energy-density demanding products. The IV group element-based materials (Si7-9, Ge10-11, Sn12) have been considered to be alternative candidates because they have higher capacities than graphite. Among them, Sn-based anodes have been extensively explored since the first commercial Sn-Co-based anode, Nexelion, was applied in LIBs by SONY Company because of the high theoretical capacity (993 mAh/g for Li4.4Sn and 847 mAh/g for Na15Sn4) and reasonable working potentials13-16. Nevertheless, the capacity fading of Sn-based anodes caused by the significant volume expansion (~260 % for Liion

battery

and

~420%

for

Na-ion

battery)

during

the

lithiation/delithiation

or

sodiation/desodiation processes hinders its practical application in commercial batteries12. In order to overcome these issues, alternative strategies have been continuously proposed, including: (i) design of Sn-M (M=active/inactive metal) alloy17-19; (ii) synthesis of Sn-SnOx structure composite20-21; (iii) preparation of Sn-C materials16, 22, etc. It has also been proved that the inactive metal (e.g., carbon) could buffer the volume expansion of Sn and result in a stable structure during cycling23. Furthermore, core-shell Sn@C structures have been shown to tolerate the volume expansion in lithation/or sodiation processes. Based on that idea, Lee et al.



synthesized core-shell Sn@C nanospheres

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through a soft template method where

tributylphenyltin (TBPT)-encapsulated resorcinol (R)−formaldehyde (F) sol was prepared inside the micelles of cetyltrimethylammonium bromide (CTAB)24. Similarly, Zhang and co-workers designed Sn@hollow carbon spheres (TNHCs) through a hard template method using SiO2 spheres and NaOH as template and etchant, respectively25. An et al. also reported yolk–shell Sn@C nanobox composites via a precipitation method, which adopted ZnSnO3 nanocubes as starting material and polydopamine (PDA) as the coating carbon source26. The ZnSnO3@PDA was thermally treated at 650 °C under H2/N2 atmosphere, resulting in yolk–shell Sn@C nanobox composites. However, all of the aforementioned methods to obtain core-shell Sn@C materials were assisted by a template or involved processing steps conducted under explosive H2 gas at a high reaction temperature, which restricted their development for the commercial rechargeable batteries. Core-shell structured particles have been reported as a promising anode material, since the free volume is enough to tolerate the expansion of core during the lithiation or sodiation27. This structure is challenging to achieve by conventional scalable chemical processes because various steps like solute precipitation, solvent evaporation, nucleation, and crystal growth have to be completed within seconds. Spray pyrolysis has proven to be one of the most practical strategies for industrial scale production of functional micro/nano-particles28-29. It is a scalable process with simple equipment requirements and operating procedures. Traditionally, to obtain the particles whose corresponding salts have low solubility in precursor solutions, spray pyrolysis normally uses strong acids to resist the salt hydrolysis29-30. Recently, a CSP process was developed to produce metal particles from precursor solutions without the direct addition of acids and H2 gas31. Unfortunately, the reported Sn/C particles mainly display structures with small Sn beads


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distributed over carbon frames. It is challenging to obtain core-shell particles due to the following aspects: i) the growth of large Sn core demands more intensified inter-colloid coagulation, which could be achieved by increasing the reaction temperature; ii) the large core has a longer diffusion length, which is an obstacle for the low diffusivity of in-situ formed H2 gas in solids32-33 and the short residence time. Thus, this chemical process development demands a detailed investigation to understand the reaction kinetics. Herein, we targeted at generating core-shell Sn@Carbon composite particles by CSP. In CSP, elevating the process temperature is a possible solution to achieve large metal or metal oxide core because the high temperature promotes the inter-colloid coagulation.31 On the other hand, the co-solvent concentration needs to be precisely controlled, or residual oxide may be expected in the products due to the longer diffusion length of H2 in solids. Therefore, in this study, we investigated in detail the chemical kinetics and aerosol dynamics of the CSP process. Guided by our model, core-shell Sn@C particles have been successfully fabricated by CSP (Figure 1a). The specially designed structure exhibits exceptional ability to maintain structural integrity during battery testing. Overall, in this work, we developed a facile, scalable, and low-cost method to produce core-shell structured Sn@C materials as high-performance anode materials in Li and Na-ion batteries without the use of a template or direct addition of explosive gas.

Methods Chemicals SnO2 colloid solution was received from Nyacol (SN15ES). The weight percent of SnO2 in aqueous solution is 15 % with specific gravity of 1.15. The particle size is 4.4 nm, as shown in 5 ACS Paragon Plus Environment


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Figure S1 (See Supplementary Information), consistent with our previous measurements34. The dark field view (Figure S1d) further validates the colloid size in the precursor solution. Sucrose was purchased from Fisher Chemical. Ethylene glycol (EG) was from Sigma-Aldrich (≥ 99 %). Ethanol (ET) was obtained from Pharmco-Aaper (≥ 99 %).

Sn@C core-shell structure fabricated by colloidal spray pyrolysis (CSP) The detailed fabrication conditions of particles used in this work are presented in Table 1. In a typical experiment, sucrose and SnO2 colloids were first added into water to form a stable solution. Then the cosolvent (ethylene glycol (EG) or ethanol (ET)) was added to make the precursor solution. The volume of the precursor solution was 150 ml. The concentration of cosolvent is tunable during the experiments to produce particles with different compositions. The precursor solutions were atomized by an ultrasonic atomizer with a 1.7 MHz transducer. The atomized droplets had a volume mean diameter of 5 µm, measured under similar experimental conditions35. The droplets were carried by the N2 gas into a quartz tube inside of two tube furnaces in series. The set points of the furnaces were 1273 K. At the end of this continuous process, the product particles were cooled by N2 gas and collected on a polytetrafluoroethylene (PTFE) filter. Based on the temperature profile of the same equipment at these conditions, the residence time of this process is 1.2 s.36 Electrode preparation and electrochemical measurements in Li/Na ion batteries. Electrochemical measurements were performed using coin cells (CR2032) assembled in an argon-filled glove box (

Rational Design of Core-Shell-Structured Particles ... - ACS Publications

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