边锋游戏

高能和大功率正极的结构特点分析
发布时间:2019-05-14 09:57:00
关键词:动力电池 锂电池

高能和大功率正极的结构特点分析


QIANYAN:ZHONGYIZHENDUANBINGREN,YAOYOU“WANGWENWENQIE”SIGEZIRUSHOU,ZHEISHISHEIDOUZHIDAODE。NEIME“WANG”PAIZAISHOUYAOWEIZHI,ZHIDESHISHENME?SUOWEI“WANG”,SHIYONGKANXIANGDEFANGFA,ZUIZHIGUANDICHAJIUBINGRENDEBINGQING。TONGLI,YAOLEJIEDIANJIDEXINGNENG,SHOUYAODEYESHIYAOGUANQIXINGMAO,ZHIQIJIEGOU,FANGNENGKEXUEDIYUGUQIXINGNENG。ZAIBENWENZHONG,KAERSILUELIGONGXUEYUANL.AlmarDENGRENTONGGUOJUJIAOLIZISHUDUANCENGSAOMIAO,FENXILESIZHONGSHANGYEGAONENGDIANCHIDAGONGLVZHENGJIDEWEIGUANJIEGOUYIJIDIANCHIZHONGDEXIANGCANSHU。ZHEISIZHONGSHANGYEDIANCHIZHENGJIFENBIEWEILiCoO2ZHENGJI (Sanyo 1500mAh),LiNiCoAlO2ZHENGJI (Sony 2600mAh),LiNiCoAlO2-LiCoO2HUNHEZHENGJI (KokamGAOGONGLV350mAh、GAONENG560mAh)。


【研究背景】


锂离子电池(LIB)是储能应用的关键器件,其规模已从mW扩大到MW级别。在很多商业锂电池中,存在着至少三种不同的相参数:

边锋游戏1)JUEDINGDIANJIRONGLIANGDEHUOXINGCAILIAOXIANG、TANHEIJIEHEXIANGHEKONGXIXIANGZHANBI;

边锋游戏2)HUOXINGWUZHIXIANGYUYETIDIANJIEZHIZHIJIANDEJIEMIANCANSHU,QIDUIDIANHEZHUANYIFANYINGZHIGUANZHONGYAO;

3)LIDUFENBU,TAJUEDINGZHELILIZIZAIHUOXINGCAILIAOXIANGZHONGDECHUANSHU。


WEILEGENGHAODELEJIETAMENZHIJIANDEXIANGHUYILAIXING,SUOYOUDEXIANGDOUXUYAOJINXINGJIHETEZHENGMIAOSHU。CONGLISHISHANGKAN,WEIGUANJIEGOUDEJIHEXIAOYINGSHITONGGUOYOUXIAODUOKONGDIANJIMOXINGLAIMIAOSHUDE,QIZHONGZUIJINGDIANDEMOXINGWEINIUMANMOXING(J. Electrochem. Soc. 109 (1962) 1183),TAWEIDIANCHISHEJITIGONGLEFEICHANGYOUJIAZHIDEXINXI,DANSHIYAOSHIGAIMOXINGDEDAODEJIEGUOGENGJIAYOUYIYI,JIUBIXUSHURUZHENGQUEDEWEIGUANJIEGOUXINXI。ZAIGUOQU,DAJIADOUJIASHEZHENGJICAILIAOSHITONGGUOQIUXINGLIZIZUCHENGDELIXIANGHUAJIEGOU,RANER,SHISHISHANG,ZHUNQUEDEWEIGUANJIEGOUCANSHUYINGGAITONGGUOGENGYOUDAIBIAOXINGDESANWEIJIEGOULAIMIAOSHU。


DUOLINGYU、DUOCHIDUZHENGJIJIEGOUDEMOXINGZHONGGOUYULIANGHUASHIYIGEPOQIEXUYAOJIEJUEDEWENTI。ZAIJIANMODESHIHOU,ZHENGJINEIBUDEGUXIANGFENLIFEICHANGZHONGYAO,TEBIESHIZAITANHEIDEHANLIANGHENDIDEQINGKUANGXIA,ZAI10nmFANWEINEI,YUEXIAODETEZHENGCHICUN、LIEXIJIEGOU、NEIBUKELIKONGXIYAOQIUYUEGAODEFENBIANLV。



JUJIAOLIZISHUSAOMIAODIANZIXIANWEIJING(FIB-SEM)CENGXICHENGXIANGCHANGYONGYUDUOKONGDIANJIDESANWEIWEIGUANJIEGOUZHONGJIAN,TONGGUOJUJIAOLIZISHUJINXINGQIEPIAN,ZAINAMIFANWEINEIKONGZHICAILIAODEJINGDU。ZAILIANXUQIEPIANGUOCHENGZHONG,ZUOZHESHOUJILESHUBAIGEERWEISAOMIAODIANJINGTUXIANG(XIANGSUDAXIAOWEI10-60 nm;JULITONGCHANGWEI10-200 nm;JIANSHANGBIAO1)。GENJUJUTISHEZHI,MEIFUTUXIANGDEXIANXUEHECHENGXIANGTONGCHANGXUYAO1FENZHONGYISHANG,YINCIDUIYUYOU500–700FUTUXIANGZUCHENGDEZHONGJIAN,ZEXUYAOYITIANYISHANGDECAIJISHIJIAN。BINGQIE,RUGUOZHONGJIANTIJIGENGDA,ZEXUYAO2-3TIANDECAIJISHIJIAN。FIB-SEMDUANCENGSAOMIAODUISANWEILIBZHONGJIANDEWENXIANZONGSHURUBIAO1SUOSHI,BIAOZHONGLIECHULEZHONGJIANTIJI、XIANGSUDAXIAO、TUXIANGJULI、TISUSHULIANGHETUXIANGSHULIANG,YIJIXIANGYINGDEZHENGJICAILIAOHEFENBIANLVDENGZHONGYAOCANSHU。KEYIKANCHU,WENXIANZHONGDEDADUOSHUZHONGJIANFENXIDEZHENGJIWEILiCoO2(LCO)HELiFePO4(LFP),ZHONGJIANLiNixMnyCo1-x-yO2(NMC)HELiMn2O4ZHENGJIDEWENXIANJIAOSHAO,GENGZHONGYAODESHI,LiNiCoAlO2 (NCA)HELiNiCoAlO2- LiCoO2 NCA/LCOZHENGJIDEZHONGJIANWANQUANMEIYOUBAODAO。



在本文中,卡尔斯鲁厄理工学院L. Almar等人对四种从功率锂离子电池中获得正极进行FIB-SEM断层扫描分析,电池的额定容量从350mAh到2600mAh,收集的体素尺寸为30-50 nm,其总体积在~19500μm~28000μm3之间。这是单个炭黑颗粒的分辨率和代表性体积元素之间的良好折衷。测试样品被硅酮渗透,采用全局和局部阈值算法对灰度值集合进行分割,较大的数据集和/或较长的铣削时间会导致灰度值分布移动,这一点非常重要。根据作者的经验,计算出的微观结构,其参数精度对这一中间阶段非常敏感。因此,作者在文章中介绍了三种不同正极的体积分数、表面积、粒径、连通性和弯曲性(活性材料、炭黑结合相和孔相)等参数设置,可以在均匀化模型中的更好的建模,并用来精确地表示电极的微观结构。上表2列出了本文中使用的所有缩略语和具体术语。

 

【研究内容】


SHIYANCANSHUDIAOKONG:


BIAO3. CONGSHANGYONGLILIZIDIANCHIZHONGTIQUSIZHONGBUTONGZHENGJIDEGUIGEHESHUJU。


BIAO4. FIB-SEMDUANCENGSAOMIAODECHUDESANWEIZHONGJIANLILIZIDIANCHIZHENGJITEXING。


SEMBIAOZHENG:

边锋游戏TU1 MEIGESHANGYONGZHENGJICAILIAOBIAOMIANDESAOMIAODIANZIXIANWEIZHAOPIAN


图1a为大功率圆柱形电池的NCA-P正极,由混合有碳纤维的LiNiCoAlO2颗粒和团聚的细碳黑颗粒制成,可以看到NCA材料形成较圆的团块,具有明显的双峰尺寸分布,由次级NCA颗粒组成。图1b中的LiCoO2 (LCO-E)由表面光滑的致密颗粒组成,团聚的、细小的炭黑颗粒非常明显,但没有碳纤维。大功率NCA/LCO-P和高能NCA/LCO-E混合正极的SEM分别如图1c和1d所示,乍一看,这两种混合正极之间没有显著差异,但混合正极中的两种活性物质LiNiCoAlO2 (NCA)和LiCoO2(LCO)可通过上述特征清楚区分。这种对于相体积、表面积、粒径分布或弯曲度的量化是非常有价值的,但不能仅基于二维数据集就进行重建,这样很容易产生误导。

 

SANWEITIJIDEFENGEHEZHONGJIAN:

图2. FIB-SEM断层扫描图像:(a) NCA-P, (b) LCO-E, (c)NCA/LCO-P,(d) NCA/LCO-E,图中显示出三个相:白色为活性材料,黑色为碳粘结剂,灰色为孔隙。


图3. 三维重建体积显示活性物质(绿色)和碳(黑色)相的分布:(a) NCA-P, (b)LCO-E, (c) NCA/LCO-P,(d) NCA/LCO-E;(e)为活性材料(AM)、碳粘结剂(CB)和每个重构正极中孔隙相的体积分数(xi)。


TU2aHE3aWEIGAOGONGLVLiNiCoAlO2(NCA-P)ZHENGJI,ZONGZHONGJIANTIJIWEI16.8×25.9×44.9 μm3,HUOXINGCAILIAO(NCA)YOUTUANJUDESHUANGFENGFENBUZUCHENG,TANXIANGZAIFENGEDETUXIANGZHONGYEKEYIQINGCHUDIFENBIANCHULAI。TU2bHE3bWEIGAONENGLiCoO2(LCO-E)ZHENGJI,ZONGZHONGJIANTIJIWEI24×25×44.35 μm3,CHUJILCOKELIZHIMI,CHICUNWEI1-8 μm,XINGZHUANGWEITUOYUAN,YUNCA-PXIANGBI,GAIZHENGJIDETANXIANGHANLIANGSIHUGENGGAO。TU2cHEdFENBIEBIAOMING,NCA/LCO-PHENCA/LCO-ELIANGZHONGHUNHEZHENGJIZHONGDENCAHELCODEKELICHICUNZAI1~8μmZHIJIAN,ERNCAZEYOU0.1~0.5μmDEXIAOCHUJIKELIZUCHENG。DAOMUQIANWEIZHI,ZHEILIANGZHONGZHENGJIZHIJIANHAIMEIYOUZHENZHENGYIYISHANGDEQUBIE,NCA/LCO-PDEZHONGJIANTIJIWEI30×21.6×32 μm3,NCA/LCO-EDEZHONGJIANTIJIWEI32.55×20.79×41.76μm3,YOUYU30 nmHE40 nmDETISUCHICUNYONGYUZHONGJIANNCA-PHELIANGZHONGHUNHEZHENGJI,DAOZHIZUOZHEYONG50 nmTISUCHICUNZHONGJIANDELCO-EZHONGWUFASHIBIETANXIANGNEITUANJUDEYIXIEKELIKONGXI。

 

边锋游戏SEM-EDXSFENXITIJIFENSHU:

边锋游戏TU4 LIYONGSEM-EDXSDUIHUNHEZHENGJIJINXINGLEJINYIBUFENXI,YIQUEDINGHUOXINGCAILIAODEXIANGXIZUCHENG


随后,作者又利用SEM-EDXS对混合正极进行了进一步分析,以确定活性材料的详细组成,上图4a为NCA/LCO-E正极的FIB-SEM图像,该正极中含有可进行能量分散X射线光谱(EDX)分析的标记区域。图4a右边的是四元素分布图,镍和钴元素来自于LiNiCoAlO2和LiCoO2活性物质颗粒,碳元素证实了碳相的存在,并没有检测到阳离子分离或任何二次相。此外,在上图4b和图4c中,NCA(绿色)和LCO(黄色)之间的分割是手动完成的。作者目前仍在开发不同活性材料之间的自动鉴别算法,并正在寻求可能的方法,包括基于特征颗粒形态或基于颗粒内晶向对比度的分割算法。但不管怎样,从上图可以看出,NCA粒子由许多次级粒子组成,由于它们的晶体取向不同,所以显示出稍微不同的灰度值,而LCO的灰度值都差不多。

 

TIJIBIBIAOMIANJI:

边锋游戏TU5 MEIGEZHENGJIHE5×5×5μm3TIJIDEGAOBEIERWEISEM,QIZHONGTANXIANGWEISHENHUISE,HUOXINGCAILIAOXIANGWEILVSE。


值得注意的是,炭黑粒子(20–30nm)的直径与体素大小(30–50 nm)的范围相同,因此测定的活性表面积有被高估或低估的风险。因此,作者仔细的分析了重建的数据集,图5比较了每个正极和5×5×5μm3体积的高倍二维SEM,其中碳相为深灰色,活性材料相为绿色。在图5a中,NCA团聚物的主要粒子在三维重建中被很好地再现,对于NCA-P正极,也可以清楚地观察到碳相(由气相生长的碳纤维和炭黑团块形成)。VGCF的长度为~3 μm,直径为~0.3 μm,通过选择一个30纳米的小体素,以上特征会变得更明显。在图b中,三维重建很好地再现了阶梯状的LCO-E正极表面,部分表面覆盖了尺寸为0.1至3μm的炭黑团块。在二维SEM中可见的主要碳黑颗粒大多低于所选体素尺寸50 nm的分辨率,因此,团聚的炭黑颗粒只能通过计算得出。图c和d均为NCA/LCO混合正极,如上所述,NCA的微观结构细节可以很好的进行3D重建。

 

LIDUFENBU:

图6. 三种不同正极活性材料粒子的二维图像及其欧几里得距离变换(EDT)映射:(a)多孔LiFePO4 (LFP)团聚体,(b)闭合后的LFP团聚体,(c)致密LiCoO2 (LCO)粒子。


边锋游戏SHANGTUSUOSHIDESHIYITUHENRONGYILIJIEGAISUANFA,ZUOZHEYILiFePO4 (LFP)HELiCoO2 (LCO)WEILI。YIGEGAODUDUOKONGDELFPTUANJUTIYAOMEBEIPINGGUWEIYIZUGENGXIAODEDANGE“CHUJI”KELI,YAOMEBEIPINGGUWEIYIGEDANGEKELI。LIYONGGAISUANFAJIANGKENENGDUANLIEDEZHIMILCOKELIFENXIWEILIANGGEKELI。


图7. 由重建正极的孔隙相计算出的粒径分布:(a) NCA-P, (b) LCO-E,(c) NCA/LCO-P,(d) NCA/LCO-E。


NCA-PYINJI(SHANGTUa)XIANSHILEQIJINWEIZHISUOYOUHUOXINGCAILIAOXIANGDEZUIXIAOPINGJUNLIZI(TUANJU)CHICUN,JUYOUSHUANGFENG(HUOSANFENG)FENBU。ZAITU7bDEHUOXINGCAILIAOLIDUTUZHONG,LCO-EZHENGJILIDU、YIJIQITANXIANGHEKONGXIANGDELIDUPINGJUNZHIFENBIEWEI1.5μm、0.4μmHE0.3μm。YOUYULCOKELISHIZHIMIDE,YINCITONGGUOEDTDEDAODEJIEGUOGENGJIEJINYUYUQIZHI。TONGGUOJIANGHUOXINGCAILIAOXIANGXUANWEIDANXIANG(NCAHELCOZHIJIANMEIYOUQUBIE),BINGGENJUZHENGGEZHONGJIANTIJI(TU7cHEd)JISUANHUNHENCA/LCOZHENGJIDELIJINGFENBUTU。KEYIDEDAOLIANGZHONGZHENGJIDEPINGJUNZHIYUHUOXINGCAILIAOXIANG1.3-1.4μm、TANXIANG0.3-0.4μmHEKONGXIANG0.3-0.4μmDEZHIJUNFEICHANGXIANGSI。

 

CAILIAOWANQUDU:


上图为计算出的弯曲度值,显然,高能电池(LCO-E andNCA/LCO-E)中的正极设计,使孔相中的弯曲度更高,分别为4.94和4.29,而高功率电池(NCA-P and NCA/LCO-P)的弯曲度分别为2.81和3.19。高功率应用的电极具有较低的弯曲度值,因为有效的离子导电性增加,高倍率下的电解质消耗可延迟。

 

【本文结论】


ZAIBENWENZHONG,ZUOZHETONGGUOJUJIAOLIZISHU(FIB)DUANCENGSAOMIAOHESANWEISHUJUFENXIJISHU,DUIGAONENGLIANGHEDAGONGLVLILIZIDIANCHIZHONGZHENGJIDEWEIGUANJIEGOUTEZHENGJINXINGLIANGHUA。SHOUCITICHULEBUTONGHUOXINGCAILIAODEGUANGFANLIANGHUA,BAOKUOJUYOUDAIBIAOXINGDEZHONGJIANTIJIYUANSU(2–3·104 μm 3)HEGAOFENBIANLV(LIFANGTITISUDAXIAOWEI30-50μm)。BENWENZHEZHONGYANJIULEYULILIZIDIANCHIZHENGJIXINGNENGXIANGGUANDEWEIGUANJIEGOUTEZHENGHEGONGYICANSHUSHEJI,DUITUANJUTIHE/HUOZHIMIXINGZHENGJIXINGCHENGDEBUTONGKELIXINGTAIJINXINGLEJINGQUEFENXI,BINGJINYIBUFENXILEKELIDENEIBUKONGXIHEZONGDEYOUXIAOBIAOMIANJI。GAIGONGZUOBUJINTIGONGLEDALIANGZHENSHIDIANJIDEWEIGUANJIEGOUSHUJU,KEZUOWEIMONIHEMOXINGDESHURUCANSHU,TONGSHIYEWEIKEXUEJIETIGONGLESHEJIZUIJIA、GAOXINGNENGLIDIANCHIDIANJIDEYIBANZHUNZE。

 

L. Almar, J. Joos, A. Weber, E. Ivers-Tiffée. Microstructural feature analysis of commercial Li-ion battery cathodes by focused ion beam tomography. Journal of Power Sources, 427 (2019) 1–14, DOI:10.1016/j.jpowsour.2019.04.019


稿件来源: 能源学人
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