LiMn2O4机械合成：吉布斯自由能与能量垒的影响
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"Effects of Gibbs free energy changes and energy barrier on mechanochemical synthesis of LiMn2O4"
在本文"Effects of Gibbs free energy changes and energy barrier on mechanochemical synthesis of LiMn2O4"中，作者赵中伟、欧阳全胜等人探讨了吉布斯自由能变化（ΔrG）和能量势垒对锂锰氧化物LiMn2O4机械化学合成的影响。这项研究是在室温条件下进行的，采用KMnO4和MnSO4·H2O作为锰源，LiOH·H2O作为锂源，通过粉末混合研磨的方式直接合成了LiMn2O4，无需后续的加热处理。
研究发现，即使在常温下，经过研磨后，初始的固态粉末混合物也能迅速形成LiMn2O4。作者特别关注了不同研磨时间对机械化学反应进程的作用，这有助于理解材料制备过程中动力学和热力学的相互作用。吉布斯自由能变化（ΔrG）是化学反应自发性的一个关键参数，当ΔrG小于零时，反应趋向于自发进行。在机械化学合成中，如果ΔrG更负，反应可能更快，因为这意味着更多的反应物质会转化为产物。
同时，能量势垒是决定反应速率的重要因素，它代表了分子克服激活能，从反应物转变为产物的难度。在研磨过程中，能量传递给粒子，可能导致足够的能量克服势垒，促使反应发生。研究揭示了研磨时间和这两个参数之间的关系，即随着研磨时间的增加，粒子间的碰撞次数增多，能量传递更充分，可能会降低能量势垒，从而加速反应进程。
此外，文章还可能讨论了如何通过控制研磨条件，如速度、时间、研磨介质等，来优化反应条件，以提高LiMn2O4的合成效率和质量。LiMn2O4是一种重要的锂离子电池正极材料，其合成方法的优化对于电池性能的提升具有重要意义。
这篇论文深入研究了吉布斯自由能变化和能量势垒在室温下LiMn2O4机械化学合成中的作用，为理解和改进此类反应提供了理论基础，并对实际的锂离子电池制造工艺具有指导价值。
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(Tianjin Kermel Chemical Reagent Development Center, China), manganese sulfate monohydrate
(MnSO
4
·H
2
O) with 99.0% purity (Chengdu Jinshan Chemical Industrial Reagent Co., Ltd., China),
electrolytic manganese dioxide (EMD, γ-MnO
2
) with 91.0% purity (Xiangtan Electric Chemical Group Co.,
Ltd, China) as Mn sources. All three reaction systems are:
(a). LiOH·H
2
O–MnSO
4
·H
2
O–KMnO
4
;
(b). LiOH·H
2
O–γ-MnO
2
;
(c). Li
2
CO
3
–γ-MnO
2
.
And the chemical equations designed to aim at synthesizing LiMn
2
O
4
within reaction systems mentioned
above are as follows:
16/5LiOH·H
2
O + 7/5MnSO
4
·H
2
O + 3/5KMnO
4
= LiMn
2
O
4
+ 4/5Li
2
SO
4
·H
2
O + 3/5KLiSO
4
+ 27/5H
2
O (1)
LiOH·H
2
O + 2γ-MnO
2
= LiMn
2
O
4
+ 3/2H
2
O + 1/4O
2
↑ (2)
1/2Li
2
CO
3
+ 2γ-MnO
2
= LiMn
2
O
4
+ 1/2CO
2
↑ + 1/4O
2
↑ (3)
Starting materials in each reaction system were weighed at a 1:2 molar ratio (Li/Mn), then subjected to
grinding in ambient air using a vibration milling (XZM–100, Wuhan Exploration Machinery Factory, China)
at a rotation speed of 960 rpm, respectively. The grinding time for each system was 35 min, stopped for 2
min to prevent an excessive temperature rise inside the reactor after 5 min, and then every 10 min operation.
For reaction system (a), such different periods of grinding time as 10 sec, 20 sec, 2 min, 8 min, 17 min and
35 min were set, especially to observe the degree of the mechanochemical reaction.
The phase analyses of ground samples were determined by a Rigaku X-Ray Diffractometer
(Dmax/2550VB+, Rigaku Corporation, Japan) using Cu Kα radiation. The tube current is 250 mA and the
voltage 40kV. The scanning rate is 8 degrees per minute, from 10–80 degree (2-Theta) with the step of 0.02
degree. MDI Jade 5 is used as analytical software for X-ray diffraction (XRD).
3 Results and Analysis
3.1 Effect of grinding time
Fig.1 shows XRD patterns of the ground samples in reaction systems from (a) to (c). As can be seen in this
figure, LiMn
2
O
4
are synthesized after grinding the solid reagents for 35 min in reaction system (a) and (b),
while only peaks of MnO
2
left in reaction system (c) along with some unknown peaks. Among the reaction
system (a) and (b), the peaks of LiMn
2
O
4
are more remarkable in the former than in the latter. Besides the
peaks of LiMn
2
O
4
, there also exist the peaks of Li
2
SO
4
·H
2
O and KLiSO
4
in reaction system (a). To observe
the peaks of LiMn
2
O
4
more clearly, the ground mixture in reaction system (a) was washed quickly by
deionized water, drained by a vacuum filter and then analyzed at once. 1b in Fig. 1 shows only the peaks of
3
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