Advanced Materials Research
ISSN: 1662-8985, Vols. 550-553, pp 2733-2737
doi:10.4028/www.scientific.net/AMR.550-553.2733
© 2012 Trans Tech Publications, Switzerland
Online: 2012-07-26
A New Type of
Reaction of N2 with Li
Yang Chi
School of Chemistry and Chemical Engineering, Mianyang Normal University, Mianyang 621000,
China
Keywords: Lithium; Nitrogen; Lithium ion battery
Abstract The reaction of N2 with lithium at electrode in lithium ion batteries was reported in this
paper. At room temperature, N2 can react with lithium, mainly at anode, to form Li3N in an
electrochemical system very easily during charge-discharge cycles. Li3N has been characterized by
XPS. Experimental results also revealed that the higher of the current density and higher of the
temperature resulted in quicker of the nitrogen-fixation reaction. The reaction can be brought about
almost completely in the lithium ion batteries at room temperature. This could be a new method for
preparation of Li3N at room temperature.
Introduction
Lithium nitride is a compound of lithium and nitrogen with the formula Li3N. It is the only
stable alkali metal nitride. The solid is in red or in purple, has a high melting
point and is ionic. It has an unusual crystal structure which consists of two different types of layers,
one sheet, composition Li2N, containing 6 coordinate lithium ions and the other consisting only of
lithium ions. Solid lithium nitride is a fast ion conductor and has the
highest conductivity of any inorganic lithium salt. It has been studied extensively as a solid
electrolyte and an anode material for batteries [1]. Lithium nitride was also being investigated as a
potential storage medium for hydrogen gas, as the reaction is reversible at 270 oC. Up to 11.5% by
weight absorption of hydrogen has been achieved [2]. Lithium nitride can be formed by direct
reaction of the elements, either by burning lithium metal in pure nitrogen gas or by reacting
nitrogen gas with lithium dissolved in liquid sodium metal [3]. Here, we introduce a novel method to
generate lithium nitride in lithium ion batteries during the charge-discharge process. When the
lithium battery system with transition metal oxides as cathode and carbon as anode is charged,
lithium ion insert into carbon to produce a layer product LiCx (x≈6) [4-13]. When N2 was used as
protective gas during the assembly of the batteries, Li3N was formed during the initial
charge-discharge cycles, associated with the dropping of the inner pressure of the batteries. This
finding could be developed for production of Li3N at room temperature.
Experimental
_
+
Cell can
Fig. 1. Cell can with vacuum gauge for pressure detection during charge-discharge cycling.
The experiments were carried out in a lithium ion battery case with the dimension of 6×45×80
mm (Fig. 1). The cathode is a set of aluminium foils coated with active cathode materials such as
La2/3-xLi3xTiO3-coated LiCoO2, while the anode is a set of copper foils coated with mesophase
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2734
Advances in Chemical Engineering II
carbon micron beads (MCMB). Each aluminium foil and copper foil was isolated by a PVDF
membrane and then subject to hot press. The Al foils and Cu foils were parallel connected to be
cathode and anode separately. The anode and cathode were soaked in electrolyte, and the spare
space (about 10%) was fully filled with protective gases (Ar or N2). The electrolyte injection hole
was connected to a capillary which was used as vacuum gauge with a diameter of 2 mm filled with
mercury.
Fig. 1. Cell can with vacuum gauge for pressure detection during charge-discharge cycling.
The cathode of the battery was layered transition metal oxides(as La2/3-xLi3xTiO3-coated
LiCoO2,etc) with MCMB as anode material and LiPF6 (1mole in EC/DMC/EMC=1/1/1) as
electrolyte. Assembly and formation of the battery was carried out in a glove-box filled with N2 or
Ar. The inner pressure was recorded after the temperature of the system coming to equilibrium with
the environment. The cycled battery was dismantled in glove-box and the electrodes were immersed
in formyl acid and water solution (50/50 wt). The reaction solution was tested to determine the
amount of reacted nitrogen. NH4+ content was tested with Ion Chromatography (US, Dionex Co).
X-ray photoelectron spectroscopy (XPS) measurement was performed on an ESCA3600 (Shimadzu)
machine, using Mg Ka (1253.6 eV) as X-ray source.
Results and discussion
The effect of the fill-in protection gas composition on the inner pressure of the lithium ion
batteries during the charge-discharge cycles was studied, as indicated in Fig. 2A. The result showed
that the inner pressure increased slightly when Ar was used as the protection gas but the inner
pressure decreased very quickly when N2 was used as the filling protection gas. On can also see
from Fig. 2A that the inner pressure decreased faster upon increase the concentration of N2. The
electrodes may expand or extract during the charge-discharge cycles because of the intercalation
and release of lithium ion, but this did not result in high vacuum of the system. The formation of a
relatively higher vacuum indicated that the N2 was reacted, most probably with metallic Li to form
a solid. As was reported, N2 can react with Li metal at room temperature slowly [3].
120
80
purified Ar
75N2/25Ar
60
50N2/50Ar
25N2/75Ar
40
20
0
0
10
20
30
Cycle number (Time)
40
50
B
-3
Purified N2
-3
Inner pressure (10 Pa)
100
110
Inner pressure of the tested cell (10 Pa)
A
105
100
95
0
10
20
30
40
50
Time (days)
Fig. 2. (A) Profile of inner pressure of the LiCoO2/MCMB batteries with different filled in gases
vs. cycle number. Temperature: 23 oC; current: 5 mA/cm2. (B) Profile of inner pressure of the
LiCoO2/MCMB battery vs. storage time at room temperature (23 oC).
On the other hand, the inner pressure of the cell only dropped slightly after 50 days without
charge-discharge cycles at room temperature (Fig. 2B). Comparing the result in Fig. 2B with that in
Fig. 2A, one can see that electric field plays a very important role in the reaction of N2 with lithium.
It is very clear that charge-discharge cycles accelerated the reaction. We noted the fact that the
charge-discharge process can activate the composite oxides on cathode and the activated oxides
could catalyze the reaction between N2 and Li. If this is true, the reaction of N2 with Li will be
affected by varying the cathode material. The change of inner pressure of the batteries during
charge-discharge cycling with different cathode materials was studied, as indicated in Fig. 3. One
can see that the inner pressure of all the batteries dropped. The pressure of the battery with graphite
Advanced Materials Research Vols. 550-553
2735
as cathode dropped slowest, while the pressure of the battery using LiCoO2 as cathode dropped
fastest. The pressure of the batteries with LiNiO2 or LiMn2O4 as cathode materials shows similar
decreasing rate at the initial 20 cycles and then decrease faster, but still lower than the one with
LiCoO2 cathode from 20 to 50 cycles.
120
MCMB/Li
LiCoO2/MCMB
LiMn2O4/MCMB
LiNiO2/MCMB
LiNi1/3Mn1/3Co1/3O2/MCMB
Inner pressure(10 Pa)
100
-3
80
60
40
20
0
0
10
20
30
40
50
Cycle number (Time)
Fig. 3. Profile of inner pressure vs. cycle number with different cathode materials. Temperature:
23 oC; atmosphere: N2.
The stability of the battery with N2 as protection gas for assembly was also examined. Fig. 4
depicts the capacity of LiCoO2/MCMB batteries in pure Ar or pure N2 during charge-discharge
cycling. One can see that the capacity of the batteries filled in with Ar or N2 shows almost the same
trend during charge-discharge cycling. The result clear indicated that the drop of the capacity of the
batteries was not because of the reaction of N2 and Li in the batteries. The decrease of the capacity
mainly comes from the irreversible reactions at the anode and cathode electrodes.
140
Ar
N2
-1
Capacity (mAh.g )
135
130
125
120
115
110
0
20
40
60
80
100 120 140 160 180 200
Cycling number (Time)
Fig. 4. Cycling life profile of LiCoO2/MCMB batteries in pure Ar and pure N2. Charge-discharge
voltage: 3.0～4.2 V; current: 5mA/cm2.
The reaction of N2 with Li took place in the electrode was supposed to according to equation
(1) because Li exists as a combination with C. It was difficult to detect Li3N directly because the
quantity of nitrogen in the battery system was limited. So we analyzed the reaction product of
cathode and anode by reacting them with formyl acid aqueous solution and found that the content of
NH4+ in the solution from anode increased with cycling process (equation 2, 3), as indicated in Fig.
5. One can see the content of NH4+ in anode increased very fast and reaches about 0.05 g per 100g
anode after 45 cycles, while it is only about 0.002 g per 100g cathode. This result clearly indicated
that the reaction of N2 and Li was at anode. On the other hand, from Fig. 3, the reaction did not
speed up with graphite as cathode and Li foil as anode, which demonstrates that the reaction of N2
with LiCx was quicker than the reaction of N2 with Li foil.
Advances in Chemical Engineering II
0.05
Anode
0.04
0.03
+
Content of NH4 (g/100g electrode)
2736
0.02
0.01
Cathode
0.00
0
10
20
30
40
50
Cycle number (Time)
Fig. 5. Profile of NH4+ content vs. cycle number at anode and cathode of the LiCoO2/MCMB
battery filled in with N2. Temperature: 23 oC; current: 3.5 mA/cm2.
N2 + 6LiCx = 2Li3N + x C
Li3N + 3H2O = NH3 + 3LiOH
NH3 + H+ = NH4+
(1)
(2)
(3)
As mentioned before, the reaction of N2 with Li in the batteries was accelerated during
charge-discharge cycling. The effect of charge-discharge current density on the change of inner
pressure was also investigated. From Fig. 6A, one can see that in a lower charge-discharge current
density, the inner pressure only dropped a little, which indicated that the reaction is very slow. With
increase of the cycling current density, the inner pressure dropped much obviously. The result
revealed that the reaction rate was increased upon increase of charge-discharge current density.
120
120
2
-3
60
40
20
80
-3
80
B
100
Inner pressure (10 Pa)
A
100
Inner pressure (10 Pa)
1.05mA/cm
2
1.75mA/cm
2
2.55mA/cm
2
3.5mA/cm
2
5.0mA/cm
2
7.0mA/cm
60
o
-10 C
o
0C
o
25 C
o
35 C
40
20
0
0
0
0
10
20
30
40
50
10
20
30
40
50
Cycle number (Time)
Cycle number (Time)
Fig. 6. (A) Effect of charge-discharge current density on variation of inner pressure. Temperature:
23 oC; current: 3.5 mA/cm2. (B) Effect of temperature on variation of inner pressure. Cathode:
LiCoO2; anode: MCMB; filled in gas: pure N2; current: 3.5 mA/cm2.
We also investigated the effect of temperature on the inner pressure during charge-discharge
cycling. As indicated in Fig. 6B, the decrease of inner pressure of the batteries was faster upon
increase of the temperature at temperature lower than 40 oC during charge-discharge cycles. At a
temperature lower than 0 oC, the reaction was very slow. It was faster at higher temperature. This is
consistent with the general principle that the higher the temperature is, the quicker the chemical
reaction is.
Advanced Materials Research Vols. 550-553
2737
Conclusion
The reaction of N2 with lithium in lithium ion batteries at room temperature was investigated.
The reaction took place at anode, and completed within the initial 30 charge-discharge cycles. The
reaction was speeded up at higher current density and higher reaction temperature. Moreover, the
reaction rate was different with different anode materials. The reaction of N2 with Li in the lithium
ion batteries at room temperature could be developed to synthesis of Li3N for nitrogen fixation.
Details of the reaction mechanism are under investigating.
Acknowledgments
This work was supported by the Foundation of Sichuan Education Department, China (Project No.
11ZA165) and Foundation of Mianyang Normal University (Project No. 2011D01)
References
[1] J. Lewis, D. Schwarzenbach, Electric field gradients and charge density in lithium nitride，Acta
Cryst. 1981,A37:507-510.
[2] P. Chen, Z. T. Xiong, J. Z. Luo, J. Y. Lin, K. L. Tan, Interaction of hydrogen with metal nitrides
and imides,Nature, 2002, 420(6913): 302-304.
[3] M. G. Barker, A. J. Blake, P. P. Edwards, M. G. Barker, A. J. Blake, P. P. Edwards, D. H.
Gregory, T. A. Hamor, D. J. Siddons, S. E. Smith, Novel Layered Lithium Nitridonickelates; Effect
of Li Vacancy Concentration on N Coordination Geometry and Ni Oxidation State, Chem.
Commun.，1999, 13:1187-1188.
[4] H. Fujimoto, M. Fujimoto, H. Ikeda, R. Ohshita, S. Fujitani, I. Yonezu, The effect of metal
sulfides in the cathode on Na/S battery performance，J. Power Sources，2001,93 : 224-226.
[5] A. Mansour, S. Schnatterly, Electronic Structure of LiC6 Studied by Soft X-Ray Emission
spectroscopy, Phys. Scr. 1987, 35:595-599.
[6] K. R. Kganyago, P. E. Ngoepe, C. R. A. Catlow, Ab initio calculation of the voltage profile for
LiC6 , Solid State Ionics, 2003,59 (2-3):21-23.
[7] K. R. Kganyago, P. E. Ngoepe, Structural and electronic properties of lithium intercalated
graphite LiC6 , Phys. Rev. B, 2003, 68 (20):205111-205126.
[8] D. Billaud, A. Hérold, F. Lincoln Vogel,Synthesis and resistivity as a function of composition
and stage for some ternary intercalation compounds,Synthetic Metals, 1981, 3( 3-4): 279-288
[9] T. D. Tran, J. H. Feikert, R. W. Pekala and K. Kinoshita,Rate effect on lithium-ion graphite
electrode performance,Journal of Applied Electrochemistry,1996, 26 (11) :1161-1167
[10] D. Billaud, F.X. Henry, P. Willmann, Electrochemical synthesis of binary graphite-lithium
intercalation compounds, Materials Research Bulletin, 1993, 28,(5): 477-483
[11] X. Y. Song, K. Kinoshita, T. D. Tran, Microstructural Characterization of Litheated Graphite ,J.
Electrochem. Soc.1996, 143 (6) :L120-L123.
[12] R. Moret, Intercalation in layered materials, NATO ASI Ser. Ed. M. S. Dresselhaus. Plenum
Press, 1986, B148.
[13] J. Rossat-Mignod, D. Fruchart, M. J. Moran, J. W. Milliken, J. E. Fisher, Application of
beta-NMR to the study of graphite intercalation compounds, Synth.Met., 1988, 23( 1-4):257-264
Advances in Chemical Engineering II
10.4028/www.scientific.net/AMR.550-553
A New Type of Reaction of N2 with Li
10.4028/www.scientific.net/AMR.550-553.2733