Optimization of LiNiO Synthetic Condition and Effect of Excess Lithium and Al Doping on Electrochemical Characteristics of the Lithium Nickel Oxides  




  

LiNiO

   
 Al  

  


 ** ** **^†

  

561-756
     1 664-14

* 

133-791    17

** 

1 Honjo, Saga 840-8502, Japan (2002 5 14  , 2002 11 11 !")

Optimization of LiNiO

Synthetic Condition and Effect of Excess Lithium and Al Doping on Electrochemical Characteristics of the Lithium Nickel Oxides

Ki Soo Park, Myung Hun Cho, Sang Ho Park*, Yang Kook Sun*, Yun Sung Lee**, Masaki Yoshio** and Kee Suk Nahm^†

School of Chemical Engineering and Technology, Chonbuk National University, 664-14, 1ga, Duckjin-dong, Duckjin-gu, Jeonju 561-756, Korea

*Department of Industrial Chemistry, College of Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Korea

**Department of Applied Chemistry, Saga University, 1 Honjo, Saga 840-8502, Japan (Received 14 May 2002; accepted 11 November 2002)



-  LiNiO2, Li_1+xNiO₂(x=0.00-0.05) LiAlyNi_1-yO₂(y=0.0-0.3)  .   

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. Al ./ Jb ./Cc de LiNiO2 f-e gch  ij ; <=>? . Al ./5 LiAlyNi_1-yO₂ kl.  ; , TUR  a? .

Abstract−LiNiO₂, Li_1+xNiO₂(x=0.00-0.05) and LiAl_yNi_1-yO₂(y=0.0-0.3) powders were synthesized using a sol-gel method.

To synthesize LiNiO₂ with a good electrochemical performance, the experiments were carried out as function of the molar ratio of adipic acid to total metal ions, excess Li content, and Al doping. The synthesized LiNiO₂ powders showed a good crystal quality when the molar ratio of adipic acid to total metal ions was 1.0. The analysis of gas composition evolved during the decomposition of gel precursors revealed that oxygen played an important role in improving the crystal quality of LiNiO₂ pow- ders. All the prepared Li_1+xNiO₂ powders had a typical LiNiO₂ layered structure, but the electrochemical performance was degraded with the increasing the lithium content. Al-doped LiAl_yNi_1-yO₂ powders were better than LiNiO₂ powders in cycli- cality though it showed a low initial discharge capacity. The Al doped LiAl_yNi_1-yO₂ powders presented a good electrochemical performance even at higher temperatures.

Key words: LiNiO₂, Excess Lithium, Al Doping, Sol-Gel

†To whom correspondence should be addressed.

E-mail: [email protected]

2

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Fig. 1. (a) Thermalgravimetric and differential thermal analysis of the gel. The molar ratio of glycolic acid to the total metal ions was 1.0. (b) Plots of partial pressures of gaseous species evolved from LiNiO₂ gel precursor during calcination as a function of decom- position temperature.

Fig. 2. X-ray diffraction patterns of LiNiO₂ powders prepared at vari- ous molar ratios of adiphic acid to total metal ions. (a) 0.5, (b) 1.0, (c) 1.5, (d) 2.0. The gel precursors were calcined at 750^oC in O₂. The upper inset showed the peak ratio of I(003)/I(104) and FWHM of (003) peak as a function of molar ratio adipic acid.

2

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3-4. Li  Li_1+xNiO₂


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 U" ](U3 v/ x[U G ƒ ­. (003)/(104) 

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(  =Ô= i'= Li U" 1.01 3 LÅ&

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Fig. 3. X-ray diffraction patterns for Li_1+xNiO₂ powders prepared at vari- ous lithium contents. The gel precursors were calcined at 750^oC in O₂. (a) Li_1.0NiO₂, (b) Li_1.01NiO₂, and (c) Li_1.02NiO₂, (d) Li_1.03NiO₂, (e) Li_1.05NiO₂. The upper inset showed the peak ratio of I(003)/

I(104) as a function of lithium content.

Fig. 4. X-ray diffraction patterns for LiAl_yNi_1-yO₂ powders prepared at various aluminum contents. The gel precursors were calcined at 750^oC in O₂. (a) Li_1.0NiO₂, (b) LiAl_0.1Ni_0.9O₂, and (c) LiAl_0.3Ni_0.7O₂. The upper inset showed the crystallite size as a function of alu- minum content.

Table 1. Lithium content and lattice constants measured by ICP and Rietveld analysis, repectrively

Narmal composition

Lattice constants

Rexp Rwp Measured

lithium content a(Å) c(Å)

Li_1.00NiO₂ 2.887 14.196 7.32 12.92 0.98 LiAl_0.1Ni_0.9O₂ 2.869 14.210 12.35 27.25 1.00 LiAl_0.3Ni_0.7O₂ 2.845 14.216 9.57 24.77 1.00

 41 1 2003 2

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¥& ¤R =Ôd – G ƒ ­. <W ‡{ Fig. 7(a)

(b)3 $C – Ï 50^oC3 ¦n LiNiO2
LiAl0.1Ni_0.9O₂3

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Li/LiPF6-EC/DMC(vol. 1:2)/Li_1+xNiO₂(and LiAl_yNi_1-yO₂) powders calcined at 750^oC in O₂. Cycling was carried out galvanostati- cally at constant charge/discharge current density of 0.4 mAcm⁻² between 3.0-4.3 V at room temperature: (a) Li_1.0NiO₂, (b) Li_1.01NiO₂, (c) Li_1.02NiO₂, (d) Li_1.0Al_0.1Ni_0.9O₂, and (e) Li_1.0Al_0.3Ni_0.7O₂.

Fig. 6. Plots of specific discharge capacity vs. number of cycles for the Li/LiPF6-EC/DMC(vol.1:2)/LiAl_yNi_1-yO₂ powders calcined at 750^oC in O₂. Cycling was carried out galvanostatically at constant charge/

discharge current density of 0.4 mAcm⁻² between 3.0-4.3 V at high temperature(50^oC). (a) Li_1.0NiO₂, (b) Li_1.0Al_0.1Ni_0.9O₂, and (c) Li_1.0 Al_0.3Ni_0.7O₂.

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