三元材料包覆改性

Improve the structure and electrochemical performance

of LiNi 0.6Co 0.2Mn 0.2O 2cathode material by nano-Al 2O 3ultrasonic

coating

Yanping Chen a ,Yun Zhang a ,⇑,Fu Wang b ,Zongyi Wang a ,Qiang Zhang a

a College of Materials Science and Engineering,Sichuan University,Chengdu 610065,PR China

b

State Key Laboratory Cultivation Base for Nonmetal Composite and Functional Materials,Southwest University of Science and Technology,Mianyang 621010,PR China

a r t i c l e i n f o Article history:

Received 29July 2013

Received in revised form 15April 2014Accepted 10May 2014

Available online 22May 2014Keywords:

Lithium ion batteries LiNi 0.6Co 0.2Mn 0.2O 2Cathode materials Nano-Al 2O 3-coating

Electrochemical performance

a b s t r a c t

The LiNi 0.6Co 0.2Mn 0.2O 2powder was coated with nano-Al 2O 3particles via ultrasonic coating,and its elec-trochemical performances were improved greatly.The X-ray diffraction,scanning electron microscopy,transmission electron microscope and energy dispersive spectroscopy were employed to research the structure variation,surface appearance and coating status.The results show that the nano-Al 2O 3particles are successfully coated and the thickness of coating layer is about 20–25nm.The XRD test results indi-cate that appropriate amount of Al 2O 3coated is beneficial to form a better layered structure with smaller cation disorder.The charge–discharge results show that LiNi 0.6Co 0.2Mn 0.2O 2coated with Al 2O 3of 1.0wt.%has initial discharge capacity of 197.1mA h g À1,initial coulombic efficiency of 91.2%at 0.2C over 2.8–4.5V and capacity retention of 91.0%much more than the pristine one of 82.9.0%after 30cycles at 1C.Especially,the rate capability of 1.0wt.%Al 2O 3-coated sample is improved evidently,it shows a high discharge capacity of 153.5mA h g À1after 5cycles under a 10C rate,whereas the pristine one is only 126.3mA h g À1under the same conditions.The electrochemical impedance spectroscopy tests results also show that the impedance of LiNi 0.6Co 0.2Mn 0.2O 2is significantly reduced by Al 2O 3coating during the cycling.

Ó2014Published by Elsevier B.V.

1.Introduction

Rechargeable lithium-ion battery is one of the most important and great appealing power sources for energy storage.LiCoO 2,as the most representative and commercial cathode material,is diffi-cult to meet the increasing requirements of today’s digital products because of its high cost,toxicity and especially low capacity.Many research have focused on Layered LiNi 1Àx Ày Co x Mn y O 2(x +y 61)cathodes because of their high specific capacity and relatively low cost [1,2].Especially,nickel-rich layered LiNi 1Àx Ày Co x Mn y O 2(1Àx Ày >0.5)cathode materials,such as LiNi 0.6Co 0.2Mn 0.2O 2have been paid more and more attentions [2–6].Cao et al.[4]reported a co-precipitation prepared LiNi 0.6Co 0.2Mn 0.2O 2which has dis-charge specific capacities of 170mA h g À1even in voltage range of 2.8–4.3V.Moreover,with the increase of voltage range from 2.8–4.3V to 2.8–4.5V,this sorts of materials will present more fas-cinating capacity performance.Nevertheless,nickel-rich cathode materials generally show also fast capacity fading [4–6]because these materials are easy to release oxygen and catalyze the decom-position of the electrolyte during cycling process [7].In addition,the strongly oxidized Ni 4+ion species can be easily dissolved into the electrolyte,especially when charged at a high voltage [8,9].All these limit the further application of nickel-rich cathode materials.

In order to resolve such problems,what usually does is that pro-tecting the surface of the cathode material from the electrolyte by coating with electrochemically inactive materials [10].The reac-tion between electrolyte and active materials leads to surface dam-age of the cathode during charge–discharge process,which may deteriorate the structural stability and decrease the capacity and cycling performance of the cell [11].Surface coating with metal oxides [12–14],phosphates [15,16]or fluorides [7,17]not only can successfully suppress these interface reactions,but also can reduce the oxygen activity of the cathode and hinder the decompo-sition of the electrolyte.

Al 2O 3,as a typical stable oxide,was widely adopted as a coating material for the surface modification of cathode materials [18–21].Xiang and Yuan [19]reported that LiNi 0.8Co 0.2O 2coated with Al 2O 3showed excellent reversible capacity and cycling stability both at room temperature and elevated temperature.To the best of our knowledge,LiNi 0.6Co 0.2Mn 0.2O 2,as a promising cathode material with better comprehensive electrochemical properties but fast capacity fading,no attention has been paid on its surface

/10.1016/j.jallcom.2014.05.0680925-8388/Ó2014Published by Elsevier B.V.

⇑Corresponding author.Tel./fax:+8602885410272.

E-mail address:y_zhang@ (Y.Zhang).