High Capacity Surface-Modified LiCoO₂ Cathodes for Lithium-Ion Batteries

Abstract

The surface of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML1" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">LiCoO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> cathodes was modified with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML2" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">Al</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mo>O</mml:mo> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> <mml:mo>,</mml:mo> </mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML3" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">TiO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo>,</mml:mo> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML4" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">ZrO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> by a chemical processing procedure followed by heat treatment at 300°C in air for 4 h. The surface-modified <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML5" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">LiCoO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> samples show much better capacity retention at both 25 and 60°C than the unmodified <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML6" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">LiCoO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> cathode to higher cutoff charge voltages of as high as 4.7 V vs. lithium. For example, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML7" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">Al</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mo>O</mml:mo> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:math> -modified <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML8" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">LiCoO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> shows approximately 180 mAh/g at 4.5 to 3.2 V with a capacity fade of only 8% in 100 cycles, compared to 32% for the unmodified <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML9" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">LiCoO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo>.</mml:mo> </mml:math> Transmission electron microscopic studies reveal that the guest materials are present as loose oxides <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML10" overflow="scroll"> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi mathvariant="normal">Al</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mo>O</mml:mo> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML11" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">ZrO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> or as monolayers <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML12" overflow="scroll"> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi mathvariant="normal">TiO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> on the surface of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="ML13" overflow="scroll"> <mml:msub> <mml:mi mathvariant="normal">LiCoO</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> particles. The improved capacity retention and the higher reversible capacity (180 mAh/g)