工程科学学报 Chinese Journal of Engineering 前驱体烘干温度对富锂锰基正极材料形貌和电化学性能的影响 杨震厉英马培华 Effect of precursor drying temperature on the morphology and electrochemical performance of lithium-rich manganese- based cathode materials YANG Zhen,LI Ying.MA Pei-hua 引用本文: 杨震,厉英,马培华.前驱体烘干温度对富锂锰基正极材料形貌和电化学性能的影响.工程科学学报,2021,43(8):1019- 1023.doi10.13374.issn2095-9389.2020.12.31.007 YANG Zhen,LI Ying,MA Pei-hua.Effect of precursor drying temperature on the morphology and electrochemical performance of lithium-rich manganese-based cathode materials[J].Chinese Journal of Engineering,2021,43(8):1019-1023.doi: 10.13374j.issn2095-9389.2020.12.31.007 在线阅读View onlines:htps/ldoi.org10.13374/.issn2095-9389.2020.12.31.007 您可能感兴趣的其他文章 Articles you may be interested in 氧化石墨烯掺杂量与H值对石墨烯气凝胶储能性能的影响 Effects of graphene oxide doping content and pH on energy storage performance of graphene aerogel 工程科学学报.2021,43(2:239 https:1doi.org/10.13374.issn2095-9389.2020.01.07.001 ZnIn LDHs在ZmNi二次电池中的电化学性能 Electrochemical properties of ZnIn LDHs in ZnNi secondary batteries 工程科学学报.2020,42(12:1624 https:doi.org10.13374j.issn2095-9389.2019.12.25.002 层状氨化硼纳米片的制备及表征 Preparation and characterization of layered boron nitride nanosheets 工程科学学报.2019,41(12:1543htps:doi.org10.13374.issn2095-9389.2019.07.04.032 锌电积过程中锰元素对铝阴极的电化学行为影响 Influence of manganese on the electrochemical behavior of an aluminum cathode used in zinc electrowinning 工程科学学报.2018,40(7):800 https:ldoi.org10.13374.issn2095-9389.2018.07.005 铝酸钠溶液种分过程中草酸钠结晶析出的行为 Behavior of sodium oxalate in seeded precipitation process of sodium aluminate solution 工程科学学报.2018,40(1:51 https:/doi.org/10.13374j.issn2095-9389.2018.01.007 吡咯/炭黑氧化物复合氧阴极材料的制备及催化性能 Preparation and catalytic studies of pyrrole-doped carbon black oxide cathode materials for oxygen reduction reactions 工程科学学报.2019,41(2:216htps:/1doi.org10.13374.issn2095-9389.2019.02.008
前驱体烘干温度对富锂锰基正极材料形貌和电化学性能的影响 杨震 厉英 马培华 Effect of precursor drying temperature on the morphology and electrochemical performance of lithium-rich manganesebased cathode materials YANG Zhen, LI Ying, MA Pei-hua 引用本文: 杨震, 厉英, 马培华. 前驱体烘干温度对富锂锰基正极材料形貌和电化学性能的影响[J]. 工程科学学报, 2021, 43(8): 1019- 1023. doi: 10.13374/j.issn2095-9389.2020.12.31.007 YANG Zhen, LI Ying, MA Pei-hua. Effect of precursor drying temperature on the morphology and electrochemical performance of lithium-rich manganese-based cathode materials[J]. Chinese Journal of Engineering, 2021, 43(8): 1019-1023. doi: 10.13374/j.issn2095-9389.2020.12.31.007 在线阅读 View online: https://doi.org/10.13374/j.issn2095-9389.2020.12.31.007 您可能感兴趣的其他文章 Articles you may be interested in 氧化石墨烯掺杂量与pH值对石墨烯气凝胶储能性能的影响 Effects of graphene oxide doping content and pH on energy storage performance of graphene aerogel 工程科学学报. 2021, 43(2): 239 https://doi.org/10.13374/j.issn2095-9389.2020.01.07.001 ZnIn LDHs在ZnNi二次电池中的电化学性能 Electrochemical properties of ZnIn LDHs in ZnNi secondary batteries 工程科学学报. 2020, 42(12): 1624 https://doi.org/10.13374/j.issn2095-9389.2019.12.25.002 层状氮化硼纳米片的制备及表征 Preparation and characterization of layered boron nitride nanosheets 工程科学学报. 2019, 41(12): 1543 https://doi.org/10.13374/j.issn2095-9389.2019.07.04.032 锌电积过程中锰元素对铝阴极的电化学行为影响 Influence of manganese on the electrochemical behavior of an aluminum cathode used in zinc electrowinning 工程科学学报. 2018, 40(7): 800 https://doi.org/10.13374/j.issn2095-9389.2018.07.005 铝酸钠溶液种分过程中草酸钠结晶析出的行为 Behavior of sodium oxalate in seeded precipitation process of sodium aluminate solution 工程科学学报. 2018, 40(1): 51 https://doi.org/10.13374/j.issn2095-9389.2018.01.007 吡咯/炭黑氧化物复合氧阴极材料的制备及催化性能 Preparation and catalytic studies of pyrrole-doped carbon black oxide cathode materials for oxygen reduction reactions 工程科学学报. 2019, 41(2): 216 https://doi.org/10.13374/j.issn2095-9389.2019.02.008
工程科学学报.第43卷,第8期:1019-1023.2021年8月 Chinese Journal of Engineering,Vol.43,No.8:1019-1023,August 2021 https://doi.org/10.13374/j.issn2095-9389.2020.12.31.007;http://cje.ustb.edu.cn 前驱体烘干温度对富锂锰基正极材料形貌和电化学性 能的影响 杨震12),厉英12)四,马培华) 1)东北大学治金学院,沈阳1108192)辽宁省治金传感器材料及技术重点实验室,沈阳110819 ☒通信作者,E-mail:liying@mal.neu.edu.cn 摘要以过渡金属硫酸盐、氢氧化钠、氨水为原料,通过连续共沉淀一高温固相法制备了富锂锰基正极材料 Li.17No.3Mn.sO2.对其进行了包括微观形貌、宏观形貌、晶体结构、电化学性能等方面的表征,研究了前驱体烘干温度对于 粒度较小前驱体的宏观形貌及锂化后正极材料的微观形貌和电化学性能的影响.结果表明,烘干温度较高的前驱体在烘干 后出现了明显了宏观烧结现象,锂化并涂布后出现了明显的颗粒;烘干温度较低的前驱体在烘干后并未出现宏观烧结现象, 锂化并涂布后未出现明显的颗粒.在电化学性能方面,前驱体烘干温度较高的正极材料在经历50个循环后,可逆比容量只剩 下85%,下降比较明显:前驱体烘干温度较低的正极材料在经历了50个循环后,可逆比容量未出现明显下降. 关键词富锂正极:前驱体:粒度:烘干:电化学性能 分类号TM912.9 Effect of precursor drying temperature on the morphology and electrochemical performance of lithium-rich manganese-based cathode materials YANG Zhen 2),LI Ying2 MA Pei-hua 1)School of Metallurgy,Northeastern University,Shenyang 110819,China 2)Liaoning Key Laboratory for Metallurgical Sensor Materials and Technology,Shenyang 110819,China Corresponding author,E-mail:liying @mail.neu.edu.cn ABSTRACT With the gradually increasing consumption of coal,oil,and natural gas and the increasing environmental pollution, recyclable secondary energy has become crucial to solving energy and environmental problems.Lithium-ion batteries have penetrated into all aspects of life.Its high energy density,high voltage platform,long life,and environment-friendly characteristics make it widely in-demand.Lithium-ion batteries are used in devices such as mobile phones,tablet computers,and electric vehicles,in which requirements of energy density,rate,and cycle performance are high.The high-capacity lithium-rich material can provide a reversible specific capacity higher than 250 mA-hgand an energy density of up to 600 W-h-kg,making it a positive electrode material.Being a scarce and strategic resource,the price of cobalt has considerably increased.The price fluctuation of cobalt directly affects the cost of the full battery.Drying conditions have a minor effect on most cathode materials and precursors and do not affect the size,morphology,and elemental distribution of their precursors.Thus,virtually no one has explored the effects of such drying conditions.Herein,we studied the drying conditions of cobalt-free lithium-rich cathode materials and explored the influence of drying condition on the morphology and electrochemical performance of cathode materials.Using sodium hydroxide,which is a transition metal sulfate,and ammonia as raw materials,a lithium-rich manganese-based cathode material (LiNio 33Mno sO2)was prepared via coprecipitation followed by sintering 收稿日期:2020-12-31 基金项目:国家自然科学基金资助项目(51834004,51774076.51474057.51904068)
前驱体烘干温度对富锂锰基正极材料形貌和电化学性 能的影响 杨 震1,2),厉 英1,2) 苣,马培华1) 1) 东北大学冶金学院,沈阳 110819 2) 辽宁省冶金传感器材料及技术重点实验室,沈阳 110819 苣通信作者,E-mail: liying@mail.neu.edu.cn 摘 要 以过渡金属硫酸盐 、氢氧化钠 、氨水为原料 ,通过连续共沉淀 – 高温固相法制备了富锂锰基正极材 料 Li1.17Ni0.33Mn0.5O2 . 对其进行了包括微观形貌、宏观形貌、晶体结构、电化学性能等方面的表征,研究了前驱体烘干温度对于 粒度较小前驱体的宏观形貌及锂化后正极材料的微观形貌和电化学性能的影响. 结果表明,烘干温度较高的前驱体在烘干 后出现了明显了宏观烧结现象,锂化并涂布后出现了明显的颗粒;烘干温度较低的前驱体在烘干后并未出现宏观烧结现象, 锂化并涂布后未出现明显的颗粒. 在电化学性能方面,前驱体烘干温度较高的正极材料在经历 50 个循环后,可逆比容量只剩 下 85%,下降比较明显;前驱体烘干温度较低的正极材料在经历了 50 个循环后,可逆比容量未出现明显下降. 关键词 富锂正极;前驱体;粒度;烘干;电化学性能 分类号 TM912.9 Effect of precursor drying temperature on the morphology and electrochemical performance of lithium-rich manganese-based cathode materials YANG Zhen1,2) ,LI Ying1,2) 苣 ,MA Pei-hua1) 1) School of Metallurgy, Northeastern University, Shenyang 110819, China 2) Liaoning Key Laboratory for Metallurgical Sensor Materials and Technology, Shenyang 110819, China 苣 Corresponding author, E-mail: liying@mail.neu.edu.cn ABSTRACT With the gradually increasing consumption of coal, oil, and natural gas and the increasing environmental pollution, recyclable secondary energy has become crucial to solving energy and environmental problems. Lithium-ion batteries have penetrated into all aspects of life. Its high energy density, high voltage platform, long life, and environment-friendly characteristics make it widely in-demand. Lithium-ion batteries are used in devices such as mobile phones, tablet computers, and electric vehicles, in which requirements of energy density, rate, and cycle performance are high. The high-capacity lithium-rich material can provide a reversible specific capacity higher than 250 mA·h·g–1 and an energy density of up to 600 W·h·kg–1, making it a positive electrode material. Being a scarce and strategic resource, the price of cobalt has considerably increased. The price fluctuation of cobalt directly affects the cost of the full battery. Drying conditions have a minor effect on most cathode materials and precursors and do not affect the size, morphology, and elemental distribution of their precursors. Thus, virtually no one has explored the effects of such drying conditions. Herein, we studied the drying conditions of cobalt-free lithium-rich cathode materials and explored the influence of drying condition on the morphology and electrochemical performance of cathode materials. Using sodium hydroxide, which is a transition metal sulfate, and ammonia as raw materials, a lithium-rich manganese-based cathode material (Li1.17Ni0.33Mn0.5O2 ) was prepared via coprecipitation followed by sintering 收稿日期: 2020−12−31 基金项目: 国家自然科学基金资助项目(51834004,51774076,51474057,51904068) 工程科学学报,第 43 卷,第 8 期:1019−1023,2021 年 8 月 Chinese Journal of Engineering, Vol. 43, No. 8: 1019−1023, August 2021 https://doi.org/10.13374/j.issn2095-9389.2020.12.31.007; http://cje.ustb.edu.cn
·1020 工程科学学报,第43卷,第8期 at 900 C.The influence of the precursor drying temperature on the macro and micro morphology and electrochemical performance was studied.The results show that the precursor displays a clear macro sintering phenomenon,and particles appear after lithiation at a higher drying temperature.The precursor with the lower drying temperature did not display a macro sintering phenomenon,and no obvious particles appeared after lithiation.After 50 cycles,the remaining capacity of the high drying temperature was only 85%,which is a significant drop.The cathode material with the lower drying temperature did not decrease significantly in capacity after 50 cycles. KEY WORDS cathode material;precursor;granularity:drying:electrochemical performance 锂离子电池作为近半个世纪发展最快的二次 由氨水作为络合剂的底液中,控制反应时的H值 能源,己经深入到生活的各个方面.高能量密度、 为10.5,反应温度为55℃以及搅拌速度800rmin, 高电压平台、寿命长、绿色环保等特点使其受到 反应时间为15h.反应完成后陈化4h,用去离子 社会的广泛关注.锂离子电池已经应用到手机、 水和酒精洗涤,分别以105和50℃烘干过夜.将 平板电脑、电动汽车等各个领域中,对其能量密度、 前驱体与氢氧化锂混合后煅烧,两段煅烧温度分 倍率和循环性能也提出了更高的要求-刀 别为450和900℃.两个样品分别命名为LL01和 高容量富锂材料可以提供高于250mAhg LLO2 的可逆比容量,能量密度高达600Whkg',使其 1.2样品表征 成为具有发展潜力的正极材料之一钴元素作 样品形貌是通过电子探针进行分析的,电压 为稀缺资源和战略资源,导致其价格飞涨,钴元素 为20kV粉末XRD(CuKa)是以5.5°min的扫 的价格波动将直接影响最终电芯的成本.特斯拉 描速度对10°~70°进行扫描.Rietveld精修是运用 已经开始降低钴元素的用量,提出“无钴化”概念, Rietica软件修正晶格参数以及NiLi混排2s-2 摆脱钴元素对电池的束缚.2019年7月9日,蜂巢 粒度测试是通过LS-POP(6)激光粒度分析仪 能源发布“全球首款基于无钴材料电芯产品,其材 进行测量.本实验采用湿法模式下测量粒度分布, 料性能可以达到NCM811同等水平,且成本可以 将样品加入到去离子水中,加入分散剂超声分散 降低5%~15%”.无钴电池不仅可以提高电性能, 一定时间,然后将其加入到激光粒度分析仪中测 提升寿命和安全性能,并且可以降低成本,摆脱正 量其粒度分布 极材料对于钴元素的依赖 1.3电化学性能测试 钴元素不仅可以提供一定的比容量,其主要 将正极材料、Super P和polyvinylidene fluoride 的作用是可以降低NLi混排,所以无钴化层状正 (PVDF)按照8:1:1的质量比进行混合,加入N- 极材料如何降低NLⅰ混排是需要研究的关键问 methyl-2-pyrrolidone(NMP)进行溶解,充分搅拌成 题,同时还需要提高安全性能、提升结构的稳定性 浆料后均匀涂布于铝箔上.真空烘干后切成15mm 和提高循环寿命等四无钴化锂离子电池的研 的圆片后压片称重,得到正极片.纯锂片作为负极, 究具有极大的挑战,与此同时,具有高能量密度的 Celgard2500作为隔膜,电解液为1 mol-L-LiPF6 低钴、无钴富锂正极材料必将成为研究的热点. ethylene carbonate(EC)diethyl Carbonate(DEC) 烘干条件对于大部分的正极材料及前驱体的 (体积比1:1)有机溶液.在手套箱中组装成 影响是较小的,不会影响其前驱体颗粒的尺寸、形 CR2032型扣式电池.采用新威高性能电池检测系 貌和元素分布等,所以几乎没有人对烘干条件进 统对组装的电池进行恒流充放电测试7 行探索.本文将针对无钴富锂正极材料的烘干条 2 结果与讨论 件进行研究,探索其对于正极材料形貌及电化学 性能的影响 2.1材料形貌和结构分析 图1为LLO1和LLO2前驱体及正极材料涂布 1实验部分 后宏观形貌.图1(a)和1(b)分别为LLO1和 1.1材料合成 LLO2不同温度烘干后的宏观形貌,图1(c)和1(d)分 Li117Nio.33Mno.sO2是通过共沉淀合成前驱体 别为LLO1和LLO2正极材料涂布后宏观形貌.从 后进行两段高温煅烧合成2).分别配制2molL1 图中可以看出,在105℃下烘干的前驱体会发生宏 的过渡金属盐溶液[nN):nMn)=2:3]和4molL- 观烧结现象,而50℃下烘干的前驱体并未发生宏观 的氢氧化钠溶液,以1.5 mLmin的速度分别泵入 烧结现象,但不排除发生微观烧结现象,说明烘干温
at 900 ℃. The influence of the precursor drying temperature on the macro and micro morphology and electrochemical performance was studied. The results show that the precursor displays a clear macro sintering phenomenon, and particles appear after lithiation at a higher drying temperature. The precursor with the lower drying temperature did not display a macro sintering phenomenon, and no obvious particles appeared after lithiation. After 50 cycles, the remaining capacity of the high drying temperature was only 85%, which is a significant drop. The cathode material with the lower drying temperature did not decrease significantly in capacity after 50 cycles. KEY WORDS cathode material;precursor;granularity;drying;electrochemical performance 锂离子电池作为近半个世纪发展最快的二次 能源,已经深入到生活的各个方面. 高能量密度、 高电压平台、寿命长、绿色环保等特点使其受到 社会的广泛关注. 锂离子电池已经应用到手机、 平板电脑、电动汽车等各个领域中,对其能量密度、 倍率和循环性能也提出了更高的要求[1–7] . 高容量富锂材料可以提供高于 250 mA·h·g–1 的可逆比容量,能量密度高达 600 W·h·kg–1,使其 成为具有发展潜力的正极材料之一[8–14] . 钴元素作 为稀缺资源和战略资源,导致其价格飞涨,钴元素 的价格波动将直接影响最终电芯的成本. 特斯拉 已经开始降低钴元素的用量,提出“无钴化”概念, 摆脱钴元素对电池的束缚. 2019 年 7 月 9 日,蜂巢 能源发布“全球首款基于无钴材料电芯产品,其材 料性能可以达到 NCM811 同等水平,且成本可以 降低 5%~15%”. 无钴电池不仅可以提高电性能, 提升寿命和安全性能,并且可以降低成本,摆脱正 极材料对于钴元素的依赖. 钴元素不仅可以提供一定的比容量,其主要 的作用是可以降低 Ni/Li 混排,所以无钴化层状正 极材料如何降低 Ni/Li 混排是需要研究的关键问 题,同时还需要提高安全性能、提升结构的稳定性 和提高循环寿命等[15–22] . 无钴化锂离子电池的研 究具有极大的挑战,与此同时,具有高能量密度的 低钴、无钴富锂正极材料必将成为研究的热点. 烘干条件对于大部分的正极材料及前驱体的 影响是较小的,不会影响其前驱体颗粒的尺寸、形 貌和元素分布等,所以几乎没有人对烘干条件进 行探索. 本文将针对无钴富锂正极材料的烘干条 件进行研究,探索其对于正极材料形貌及电化学 性能的影响. 1 实验部分 1.1 材料合成 Li1.17Ni0.33Mn0.5O2 是通过共沉淀合成前驱体 后进行两段高温煅烧合成[23] . 分别配制 2 mol·L–1 的过渡金属盐溶液 [n(Ni)∶n(Mn)=2∶3] 和 4 mol·L–1 的氢氧化钠溶液,以 1.5 mL·min–1 的速度分别泵入 由氨水作为络合剂的底液中,控制反应时的 pH 值 为 10.5,反应温度为 55 ℃ 以及搅拌速度 800 r·min–1 , 反应时间为 15 h. 反应完成后陈化 4 h,用去离子 水和酒精洗涤,分别以 105 和 50 ℃ 烘干过夜. 将 前驱体与氢氧化锂混合后煅烧,两段煅烧温度分 别为 450 和 900 ℃. 两个样品分别命名为 LLO1 和 LLO2. 1.2 样品表征 样品形貌是通过电子探针进行分析的,电压 为 20 kV[24] . 粉末 XRD(Cu Kα)是以 5.5°·min–1 的扫 描速度对 10°~70°进行扫描. Rietveld 精修是运用 Rietica 软件修正晶格参数以及 Ni/Li 混排[25–26] . 粒度测试是通过 LS-POP(6) 激光粒度分析仪 进行测量. 本实验采用湿法模式下测量粒度分布, 将样品加入到去离子水中,加入分散剂超声分散 一定时间,然后将其加入到激光粒度分析仪中测 量其粒度分布. 1.3 电化学性能测试 将正极材料、Super P 和 polyvinylidene fluoride (PVDF)按照 8∶1∶1 的质量比进行混合,加入 Nmethyl-2-pyrrolidone(NMP)进行溶解,充分搅拌成 浆料后均匀涂布于铝箔上. 真空烘干后切成 15 mm 的圆片后压片称重,得到正极片. 纯锂片作为负极, Celgard2500 作为隔膜 ,电解液为 1 mol·L–1 LiPF6 的 ethylene carbonate(EC)和 diethyl Carbonate(DEC) (体积 比 1∶1)有机溶液 . 在手套箱中组装 成 CR2032 型扣式电池. 采用新威高性能电池检测系 统对组装的电池进行恒流充放电测试[27] . 2 结果与讨论 2.1 材料形貌和结构分析 图 1 为 LLO1 和 LLO2 前驱体及正极材料涂布 后 宏 观 形 貌 . 图 1( a) 和 1( b) 分 别 为 LLO1 和 LLO2 不同温度烘干后的宏观形貌,图 1(c)和 1(d)分 别为 LLO1 和 LLO2 正极材料涂布后宏观形貌. 从 图中可以看出,在 105 ℃ 下烘干的前驱体会发生宏 观烧结现象,而 50 ℃ 下烘干的前驱体并未发生宏观 烧结现象,但不排除发生微观烧结现象,说明烘干温 · 1020 · 工程科学学报,第 43 卷,第 8 期
杨震等:前驱体烘干温度对富锂锰基正极材料形貌和电化学性能的影响 1021· 度对于前驱体的宏观形貌存在明显的影响.LLO1样 表面光滑,并未出现明显的颗粒,说明烘干温度对于 品涂布后表面出现明显的颗粒,而LLO2样品涂布后 正极材料涂布后宏观形貌也具有较大的影响. (a) (b) (c) d 图1LLO1和LLO2前驱体及正极材料涂布后宏观形貌.(a)LLO1前驱体:(b)LLO2前躯体:(c)LLO1正极材料:(d)LLO2正极材料 Fig.1 Macro morphology of precursor and cathode materials:(a)precursor of LLOl;(b)precursor of LLO2;(c)cathode material of LLO1;(d)cathode material of LLO2 图2为存在大颗粒的样品辊压后宏观形貌 图3为LLO1和LLO2样品的微观形貌.其中 图中颗粒明显并且在辊压过后,部分颗粒出现脱 LLO1和LLO2均由不规则形貌的小颗粒组成,其 落现象,导致正极材料极片不合格,说明正极材料 微观形貌的差异较小,而涂片后出现明显的大颗 制备过程中应尽量避免大颗粒的出现导致粒度不 粒,可能是调浆过程造成的 均匀.即使大颗粒未发生脱落,也会导致极片的能 图4为LLO1和LLO2样品XRD图及精修后 量密度存在差异,电化学性能的不稳定性增加. 图谱.Rietveld精修后具体参数如表l,表中a和 c表示晶格常数,1oo3/1o4表示衍射峰强度比,Nii 表示Ni与Li的混排度,Bragg R、R,、Rwp和X均表 示精修的准确度.XRD衍射表明两种样品均具有 a-NaFe02的R-3m空间群,在20°到25°具有Li2MnO3 ⊙ 的C2m空间群,Ioo3/1o4值均大于1.2,表明所合 成的材料层状结构完整,LLO1和LLO2的NiLi混 排分别为2.87%和3.04%,说明Ni/Li混排较小 LLO1和LLO2的(006)(102)与(108)/(110)两对衍 图2存在大颗粒的样品辊压后宏观形貌 Fig.2 Macroscopic morphology of samples with large particles after 射峰分裂明显,衍射峰峰形尖锐,表明材料结晶度 rolling 良好 1μm 图3LLO1(a)和LLO2(b)样品的微观形貌 Fig.3 Electron microprobe images of LLOI sample (a)and LLO2 sample(b)
度对于前驱体的宏观形貌存在明显的影响. LLO1 样 品涂布后表面出现明显的颗粒,而 LLO2 样品涂布后 表面光滑,并未出现明显的颗粒,说明烘干温度对于 正极材料涂布后宏观形貌也具有较大的影响. (a) (b) (c) (d) 图 1 LLO1 和 LLO2 前驱体及正极材料涂布后宏观形貌. (a)LLO1 前驱体;(b)LLO2 前躯体;(c)LLO1 正极材料;(d)LLO2 正极材料 Fig.1 Macro morphology of precursor and cathode materials: (a) precursor of LLO1; (b) precursor of LLO2; (c) cathode material of LLO1; (d) cathode material of LLO2 图 2 为存在大颗粒的样品辊压后宏观形貌. 图中颗粒明显并且在辊压过后,部分颗粒出现脱 落现象,导致正极材料极片不合格,说明正极材料 制备过程中应尽量避免大颗粒的出现导致粒度不 均匀. 即使大颗粒未发生脱落,也会导致极片的能 量密度存在差异,电化学性能的不稳定性增加. 图 2 存在大颗粒的样品辊压后宏观形貌 Fig.2 Macroscopic morphology of samples with large particles after rolling 图 3 为 LLO1 和 LLO2 样品的微观形貌. 其中 LLO1 和 LLO2 均由不规则形貌的小颗粒组成,其 微观形貌的差异较小,而涂片后出现明显的大颗 粒,可能是调浆过程造成的. 图 4 为 LLO1 和 LLO2 样品 XRD 图及精修后 图谱. Rietveld 精修后具体参数如表 1,表中 a 和 c 表示晶格常数,I(003)/I(104) 表示衍射峰强度比,NiLi 表示 Ni 与 Li 的混排度,Bragg R、Rp、Rwp 和 χ 2 均表 示精修的准确度. XRD 衍射表明两种样品均具有 α-NaFeO2 的 R-3m 空间群,在 20°到 25°具有 Li2MnO3 的 C2/m 空间群,I(003)/I(104) 值均大于 1.2,表明所合 成的材料层状结构完整,LLO1 和 LLO2 的 Ni/Li 混 排分别 为 2.87% 和 3.04%, 说 明 Ni/Li 混排较小 . LLO1 和 LLO2 的 (006)/(102) 与 (108)/(110) 两对衍 射峰分裂明显,衍射峰峰形尖锐,表明材料结晶度 良好. 1 μm (a) 1 μm (b) 图 3 LLO1(a)和 LLO2(b)样品的微观形貌 Fig.3 Electron microprobe images of LLO1 sample (a) and LLO2 sample (b) 杨 震等: 前驱体烘干温度对富锂锰基正极材料形貌和电化学性能的影响 · 1021 ·
1022 工程科学学报,第43卷,第8期 (a) Raw (b) Raw Fitted Fitted Diff 一Diff R-3m peaks -R-3m peaks 10 20 30 40 50 60 70 10 20 30 40 50 60 70 28l) 20/) 图4LLO1(a)和LLO2(b)样品XRD图及精修后图谱 Fig.4 XRD pattern and Rietveld refinement results of LLOI sample (a)and LLO2 sample (b) 表I不同样品的Rietveld精修结果表 2.2材料的电化学性能 Table 1 Summary of Rietveld refinement results 图5为LLO1和LLO2的倍率性能和循环性 能.LLO1样品在1C(1C=250mAg)循环50圈后 Sample a/nm c/nm oo3y1(04)NiL Bragg R Rp Rwp 容量只剩下85%,而LLO2样品在1C循环50圈后 LL010.286691.425662.012.87%0.771.962.791.748 容量未出现明显下降.LLO2的倍率性能和循环性 LL020.286421.42382 2.403.04%1.022.152.981.795 能均优于LLO1. 250 200 (a) (b) 200 83. 175 e净参垂制 aee●多 25 博e原年e净中。 125 150 125 色9aee。a中 125 250 ●ee0 500688% 100 75 LLOI 1750 LLO2 50 50 e ae LLOI 1250 *LLO2 Current unit:mA'g 25 0 0 0 5 10 152025 30 35 40 0 10 20 30 40 50 Cycle number Cycle number 图5LLO1和LLO2的倍率(a)及循环性能(b) Fig.5 Rate capacity (a)and cycling capacity (b)of LLOl and LLO2 LLO1和LLO2样品的电化学性能出现明显的 前驱体烘干温度不同,导致前驱体可能出现 差异,其主要原因是烘干温度不同所导致的.富锂 明显的烧结现象.而前驱体制备的形貌、元素分 材料由于倍率和循环性能较差,所以在制备LLO1 布等将传递给正极材料.当前驱体发生烧结现象, 和LLO2样品的前驱体时,所制备的前驱体粒度均 研磨粉碎后会对混锂、摻杂、包覆等一系列合成 较小,用于改善其倍率和循环性能.前驱体的粒度 及改性产生较大的影响.所以在前驱体烘干时控 较小时具有较大的表面自由能,具有较高的活性 制烘干温度十分重要 烘干温度较高时,LLO1样品前驱体出现烧结现 3结论 象,手动研磨粉碎后,导致颗粒表面粗糙.LLO2样 品前驱体未出现烧结现象,无大颗粒出现,颗粒表 富锂材料前驱体粒度较小时,导致其表面自 面的光滑程度将大大提升.由图3可知,LLO1和 由能较高,较高的烘干温度导致前驱体出现明显 LLO2样品的微观形貌差异较小,所以涂片后大颗 的宏观烧结现象,前驱体锂化涂布后出现明显的 粒的出现很可能是调浆时由于PVDF和NMP的 颗粒:较低的烘干温度未发生明显的宏观烧结现 作用而粘到一起的. 象,前驱体锂化涂布后未出现明显的颗粒.前驱体
2.2 材料的电化学性能 图 5 为 LLO1 和 LLO2 的倍率性能和循环性 能. LLO1 样品在 1C(1C=250 mA·g−1)循环 50 圈后 容量只剩下 85%,而 LLO2 样品在 1C 循环 50 圈后 容量未出现明显下降. LLO2 的倍率性能和循环性 能均优于 LLO1. LLO1 和 LLO2 样品的电化学性能出现明显的 差异,其主要原因是烘干温度不同所导致的. 富锂 材料由于倍率和循环性能较差,所以在制备 LLO1 和 LLO2 样品的前驱体时,所制备的前驱体粒度均 较小,用于改善其倍率和循环性能. 前驱体的粒度 较小时具有较大的表面自由能,具有较高的活性. 烘干温度较高时,LLO1 样品前驱体出现烧结现 象,手动研磨粉碎后,导致颗粒表面粗糙. LLO2 样 品前驱体未出现烧结现象,无大颗粒出现,颗粒表 面的光滑程度将大大提升. 由图 3 可知,LLO1 和 LLO2 样品的微观形貌差异较小,所以涂片后大颗 粒的出现很可能是调浆时由于 PVDF 和 NMP 的 作用而粘到一起的. 前驱体烘干温度不同,导致前驱体可能出现 明显的烧结现象. 而前驱体制备的形貌、元素分 布等将传递给正极材料. 当前驱体发生烧结现象, 研磨粉碎后会对混锂、掺杂、包覆等一系列合成 及改性产生较大的影响. 所以在前驱体烘干时控 制烘干温度十分重要. 3 结论 富锂材料前驱体粒度较小时,导致其表面自 由能较高,较高的烘干温度导致前驱体出现明显 的宏观烧结现象,前驱体锂化涂布后出现明显的 颗粒;较低的烘干温度未发生明显的宏观烧结现 象,前驱体锂化涂布后未出现明显的颗粒. 前驱体 表 1 不同样品的 Rietveld 精修结果表 Table 1 Summary of Rietveld refinement results Sample a/nm c/nm I(003)/I(104) NiLi Bragg R Rp Rwp χ 2 LLO1 0.28669 1.42566 2.01 2.87% 0.77 1.96 2.79 1.748 LLO2 0.28642 1.42382 2.40 3.04% 1.02 2.15 2.98 1.795 10 20 Intensity 30 40 (a) 2θ/(°) 50 60 70 Raw Fitted Diff R-3m peaks (b) 10 20 Intensity 30 40 2θ/(°) 50 60 70 Raw Fitted Diff R-3m peaks 图 4 LLO1(a)和 LLO2(b)样品 XRD 图及精修后图谱 Fig.4 XRD pattern and Rietveld refinement results of LLO1 sample (a) and LLO2 sample (b) 0 0 50 100 150 200 250 5 Specific capacity/(mA·h·g−1 ) 10 15 (a) Cycle number Current unit: mA·g−1 25 50 125 250 500 750 1250 25 20 25 30 35 40 LLO1 LLO2 0 0 50 75 25 100 125 175 150 200 Specific capacity/(mA·h·g−1 ) (b) Cycle number 10 20 30 40 50 LLO1 LLO2 图 5 LLO1 和 LLO2 的倍率(a)及循环性能(b) Fig.5 Rate capacity (a) and cycling capacity (b) of LLO1 and LLO2 · 1022 · 工程科学学报,第 43 卷,第 8 期
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