匯報ppt-鋰離子電池電極力學(xué)失效研究

1、1,鋰離子電池電極力學(xué)失效研究,1. 研究背景——問題的提出,,2. 目前研究狀況,3. 我們的工作設(shè)想,2,1. 研究背景,近年來用于手機、數(shù)碼相機和筆記本電腦中的鋰離子電池爆炸傷人事件已經(jīng)屢見不鮮，鋰離子電池的安全問題引起人們廣泛的關(guān)注。僅2009年5月份就發(fā)生了若干起與鋰離子電池相關(guān)的安全事故，其中包括HTC Touch Pro原裝電池燃燒事件，以及惠普筆記本電腦電池召回事件。惠普公司給出的召回原因是那些電池存在過熱起火和燙傷消費

2、者的隱患，據(jù)說該電池組發(fā)生過至少兩起事故，主要是因為電池過熱、破裂導(dǎo)致起火。目前報道的鋰離子電池安全問題集中發(fā)生在用于數(shù)碼產(chǎn)品上的小型鋰離子電池，與手機電池相比，筆記本電腦電池由于容量更高，出現(xiàn)問題的幾率也相對較高；而用于交通工具上大型的動力電池或電池組，其安全問題更為突出，目前安全問題已成為制約鋰離子電池向大型化、高能化方向發(fā)展的瓶頸。,3,,手機安全隱患嚴重，爆炸起火似不定時炸彈,4,,在錯誤的條件下使用錯誤的電池會造成故障和爆炸。

3、仔細的設(shè)計就會避免電池破裂和爆炸等意外，減少有害的電化學(xué)反應(yīng)和失誤帶來的風險。鋰離子電池具有很多優(yōu)于其他可充電電池的特性，包括高能量密度、重量輕、生命周期長、容量保持特性好、環(huán)境溫度適應(yīng)范圍大和電流忍耐能力強，等等。鋰離子電池對環(huán)境的適應(yīng)能力比其他化學(xué)電池要強，但是大容量的特點則意味著電池組必須要設(shè)計得更加安全。 圖1  安全設(shè)計可避免很多事故,5,,,6,,,7,,從1991 年日本SONY 公司首次推出商

4、品化鋰離子電池產(chǎn)品算起，鋰離子電池發(fā)展至今已有接近20 年的歷史。鋰離子電池( lithium ion battery) 是指以嵌鋰化合物作為正/ 負極材料的電池。嵌鋰化合物多為層狀或框架結(jié)構(gòu)，充放電過程中鋰離子可在其層間可逆的嵌入與脫出而不改變其結(jié)構(gòu)。,8,,鋰離子電池是繼鎳鎘電池和金屬氫化物鎳電池之后的第2代可充電“綠色電池” 。由于這種電池的正極材料的容量比負極材料的要低，所以限制了鋰離子電池容量進一步提高。鋰鈷、鋰鎳和鋰錳氧化物

5、材料是3種主要的鋰離子電池正極材料，其中鋰錳氧化物材料以其制備成本低、無環(huán)境污染、電化學(xué)比容量有效利用率高而擁有廣泛的開發(fā)應(yīng)用前景，鋰錳電池已成為人們廣泛關(guān)注的焦點。,9,,應(yīng)用于電動車鋰離子電池的電極,10,,法國研制出高能鋰離子電池電極,11,,圖1 橄欖石型LiFePO4結(jié)構(gòu)示意圖,12,2. 目前研究狀況,Yuhang Hu, Xuanhe Zhao, and Zhigang Suo, Averting cracks cause

6、d by insertion reaction in lithium-ion batteries. J. Mater. Res., Vol. 25, No. 6, Jun 2010,13,,FIG.1 . Insertion-induced deformation may be constrained by the mismatch between active and inactive materials, between grain

7、s of different orientations, and between phases of different concentrations of lithium. The constrained deformation leads to stresses, which may cause the electrode to crack.,14,,FIG. 2. In a crystal of LiFePO4, lithium

8、atoms diffuse along tunnels in direction b, and cleavage may occur on the bc and ac planes.,15,,,,,,,,,,,16,,FIG. 3. Energy release rate for a crack on the phase boundary in a platelike LiFePO4 particle.,17,,FIG. 4. In a

9、n equiaxed LiFePO4 particle, energy release rate of (a) a crack in a phase and (b) a crack on the phase boundary.,18,,Kejie Zhao, Matt Pharr, Joost J. Vlassak, and Zhigang Suo, Fracture of electrodes in lithium-ion batte

10、ries caused by fast charging, JOURNAL OF APPLIED PHYSICS 108, 073517 (2010).Using a combination of diffusion kinetics and fracture mechanics, we have outlined a theory to study how material properties, particle size, an

11、d discharge rate affect fracture of electrodes in lithium-ion batteries.,19,,Kejie Zhao, Matt Pharr, Shengqiang Cai, Joost J. Vlassak, and Zhigang Suo, Large Plastic Deformation in High-Capacity Lithium-Ion Batteries Cau

12、sed by Charge and Discharge, J. Am. Ceram. Soc., 94 [S1] S226–S235 (2011).Evidence has accumulated recently that a high-capacity electrode of a lithium-ion battery may not recover its initial shape after a cycle of char

13、ge and discharge. Such a plastic behavior is studied here by formulating a theory that couples large amounts of lithiation and deformation. The homogeneous lithiation and deformation in a small element of an electrode un

14、der stresses is analyzed within nonequilibrium thermodynamics, permitting a discussion of equilibrium with respect to some processes, but not others.,20,,Kejie Zhao, Matt Pharr, Lauren Hartle, Joost J. Vlassak, Zhigang S

15、uo， Fracture and debonding in lithium-ion batteries with electrodes of hollow coreeshell nanostructures， Journal of Power Sources ，218 (2012) ，6-14。In a novel design of lithium-ion batteries, hollow electrode particles

16、coated with stiff shells are used to mitigate mechanical and chemical degradation. In particular, silicon anodes of such coreeshell nanostructures have been cycled thousands of times with little capacity fading. To reduc

17、e weight and to facilitate lithium diffusion, the shell should be thin. However, to avert fracture and debonding from the core, the shell must be sufficiently thick.,21,,Fig. 1. (a). For a silicon particle without a stif

18、f shell (b). Also for a silicon particle without a stiff shell, the deformation associated with lithiation and delithiation may cause the shedding and re-forming of the solid-electrolyte interphase (SEI), consuming acti

19、ve materials. (c). For a hollow silicon particle with a stiff shell, the deformation of silicon is accommodated by inward swelling, so that electric contact is maintained, and the shedding of SEI avoided.,22,,Fig. 2. Two

20、 potential modes of failure in a hollow silicon particle coated with a stiff shell. (a). The lithiation of the silicon particle induces tensile hoop stress in the shell, which may cause the shell to fracture. (b) The del

21、ithiation of the silicon particle induces radial tensile stress, which may cause debonding between the core and the shell.,23,,Fig. 3. (a). In the reference state, a hollow particle of an electrode is stress-free and lit

22、hium-free. (b) In the current state, the particle is partially lithiated. The deformation of the core is accommodated by the inner hollow space. Outward deformation is restricted by the shell.,24,,,(2),(3),(4),(7),(5),(9

23、),(6),(8),,,25,,Fig. 4. Evolution of the radial stress at the interface between the particle and the shell during lithiation and delithiation.,26,,Analysis of coated hollow silicon nanowires,,,,,,27,,Fig

24、. 6. Conditions of fracture and debonding for a hollow nanowire plotted in the plane of (a) the thickness of the shell and the state of charge, and (b) the radius of the particle and the state of charge.,28,3. 我們的工作設(shè)想,熱、