用於合成磷酸鐵鋰－碳組成物之方法Method for synthesizing lithium iron phosphate-carbon composition
本發明係關於一種用於合成磷酸鐵鋰-碳組成物之方法，且也關於所得之組成物，以及關於包含該組成物之陰極和電池。The present invention relates to a method for the synthesis of a lithium iron phosphate-carbon composition, and also to the resulting composition, as well as to cathodes and batteries comprising this composition.
有需要一種具有改良功率之陰極材料，尤其是意圖用於電動車輛之電池。對於中程(medium-range vehicle)車輛所考慮之不昂貴材料包括磷酸鐵鋰(LFP)及其衍生物(LFMP-部分鐵被錳或鈷取代)。再者，包含LFP之電池耐受更多再充電循環且耐受高強度，而使彼等能供應很多電量且能快速地再充電。最後，包含LFP之電池具有較低的可點燃性而使彼等能在高達70℃之溫度下使用。
該材料是差的導電體，且為了改良此問題，已藉由結合LFP與碳來尋求不同策略，已有不同程度的成功。對於此種LFP/碳結合物，本申請人使用『組成物』一詞，但在文獻中常出現『複合材料』一詞。二種名詞被視為意指相同的材料。在2017年1月1日之中國非鐵金屬學會會刊第141至147頁，『藉由噴霧乾燥方法合成用於鋰離子電池之多孔性奈米/微米結構化LiFePO
4/C陰極材料』(“Synthesis of porous nano/micro structured LiFePO
4/C cathode materials for lithium-ion batteries by spray-drying method”, Transactions of Nonferrous Metals Society of China, 1 Janyary 2017, pages 141-147)中，作者將LFP與漿料形式的碳前驅物混合以提供多孔性且結構化的球狀材料。該方法包括噴霧，接著在700℃下鍛燒。該方法使該LFP之表面具傳導性，但該等粒子的內部顯然不受此改良的影響。
WO2011117530在實例11中描述一種合成方式，其中LFP與碳奈米管(CNT)結合。此方法不會在該LFP粒子內產生傳導性網絡。
在奈米科學及奈米技術期刊2013年8月1日13(8):5440-5444，『藉由固態反應所合成之用於鋰離子電池的C-LFP-多壁型碳奈米管複合陰極材料』(“C-LFP-multi-walled carbon nanotubes composite cathode materials synthesized by solid-state reaction for lithium ion batteries”, Journal of Nanoscience and Nanotechnology, 1 Aug 2013, 13(8):5440-5444)中，使用多壁型碳奈米管(MWNT)與LFP前驅物於合成中。藉由在C-LFP之合成的不同步驟中摻混MWNTs而製備複合材料。作者比較下列二種材料的效能：藉由在750℃及還原氣體環境下鍛燒之前預先摻混(PrB) MWNT與LFP前驅物所製作之複合材料，和藉由後摻混(PoB) MWNT與LFP所製作之複合材料。後者材料獲得較低效能。然而，稱為PrB之合成反應係在固態中進行，這事實上限制該奈米碳管在所得之組成物中之均勻分散性。
在另一刊物-RCS Advances，2015年，5,47,37830-37836頁，『用於高效能鋰離子電池陰極材料之多孔性微球形LiFePO
4/CNT奈米複合材料』(“Porous micro-spherical LiFePO
4/CNT nanocomposite for high-performance Li-ion battery cathode material”, RCS Advance, 2015, 5, 47, p37830-37836)中，將直徑20至30nm的奈米管氧化以形成表面氧化的基團且然後在攪拌下分散在水中。在超音波作用下，將硝酸鐵以及磷酸二氫銨添加於此。將該混合物加熱至180℃。獲得FePO
4/MCNT複合材料。以碳覆蓋之步驟包含藉由與葡萄糖、氫氧化鋰和FePO
4/MCNT粉末一同研磨以混合。接著是在還原氣體環境下處理。最高溫度是700℃且該處理持續10小時。該方法在該LFP凝集體內部提供傳導性粒子，但非穩定化奈米管之使用在該合成期間導致再黏聚和在該奈米管中之效率損失。此外，超音波之使用切割並氧化該等碳奈米管，導致效能損失。
申請人因此已尋求透過一種原初方法以結合LFP和碳奈米管，該原初方法得以藉由使用球磨機而限制該碳奈米管之機械降解及氧化，同時維持其良好分散，使得該LFP前驅物能在與該碳奈米管極密切接觸時產生LFP。該碳奈米管係利用羧甲基纖維素之鹼金屬陽離子(例如鈉)在該水相中被穩定化，且該LFP直接在該碳奈米管上被合成。
在該方法中，水之使用可能降低獲得關於該LFP所要之橄欖石結構所需之溫度，因此促使該鋰良好嵌入。此新穎方法可能減小該LFP中之微傳導區的尺寸。任意之以碳覆蓋所得之組成物的額外步驟可能進一步明顯改良使用本方法所得之該新穎組成物的傳導性質。
There is a need for a cathode material with improved power, especially for batteries intended for electric vehicles. Inexpensive materials considered for medium-range vehicles include Lithium Iron Phosphate (LFP) and its derivatives (LFMP - partial iron replaced by manganese or cobalt). Furthermore, batteries containing LFP withstand more recharge cycles and withstand high intensities, allowing them to supply large amounts of power and to recharge quickly. Finally, batteries comprising LFP have lower ignitability enabling them to be used at temperatures as high as 70°C. This material is a poor electrical conductor, and to ameliorate this problem, different strategies have been pursued, with varying degrees of success, by combining LFP with carbon. For this LFP/carbon combination, the applicant uses the term "composition", but the term "composite material" often appears in the literature. Both nouns are considered to mean the same material. On January 1, 2017, the Journal of the Chinese Society of Nonferrous Metals, pages 141 to 147, "Synthesis of porous nano/micro-structured LiFePO 4 /C cathode materials for lithium-ion batteries by spray drying method" ( "Synthesis of porous nano/micro structured LiFePO 4 /C cathode materials for lithium-ion batteries by spray-drying method", Transactions of Nonferrous Metals Society of China, 1 January 2017, pages 141-147), the author combined LFP with slurry Carbon precursors in the form of pellets are mixed to provide porous and structured spherical materials. The method involves spraying followed by calcination at 700°C. This method made the surface of the LFP conductive, but the interior of the particles was apparently not affected by this modification. WO2011117530 describes in Example 11 a synthesis in which LFP is combined with carbon nanotubes (CNTs). This method does not create a conductive network within the LFP particle. In Nanoscience and Nanotechnology Journal 13(8):5440-5444, August 1, 2013, "C-LFP-Multi-walled Carbon Nanotube Composite Synthesized by Solid State Reaction for Li-ion Batteries Cathode materials” (“C-LFP-multi-walled carbon nanotubes composite cathode materials synthesized by solid-state reaction for lithium ion batteries”, Journal of Nanoscience and Nanotechnology, 1 Aug 2013, 13(8):5440-5444), Using multi-walled carbon nanotubes (MWNT) and LFP precursors in the synthesis. Composite materials were prepared by blending MWNTs in different steps of the synthesis of C-LFP. The authors compared the performance of the following two materials: composites fabricated by pre-blending (PrB) MWNTs with LFP precursors prior to calcination at 750 °C in a reducing gas atmosphere, and by post-blending (PoB) MWNTs with Composite materials made by LFP. The latter material achieves lower performance. However, the synthesis reaction known as PrB is carried out in the solid state, which in fact limits the homogeneous dispersion of the carbon nanotubes in the resulting composition. In another publication - RCS Advances, 2015, pages 5, 47, 37830-37836, "Porous micro-spherical LiFePO 4 /CNT nanocomposites for high-efficiency lithium-ion battery cathode materials"("Porous micro-spherical LiFePO 4 /CNT nanocomposite for high-performance Li-ion battery cathode material”, RCS Advance, 2015, 5, 47, p37830-37836), the nanotubes with a diameter of 20 to 30 nm are oxidized to form surface oxidized groups and Then disperse in water with stirring. Under the action of ultrasonic waves, iron nitrate and ammonium dihydrogen phosphate are added here. The mixture was heated to 180°C. A FePO 4 /MCNT composite material was obtained. The step of carbon coating involved mixing by grinding with glucose, lithium hydroxide and FePO4 /MCNT powder. This is followed by treatment under a reducing gas environment. The maximum temperature was 700°C and the treatment lasted 10 hours. This method provides conductive particles inside the LFP aggregates, but the use of non-stabilized nanotubes leads to reagglomeration and loss of efficiency in the nanotubes during the synthesis. In addition, the use of ultrasound cuts and oxidizes the carbon nanotubes, resulting in loss of efficiency. Applicants have therefore sought to combine LFP and carbon nanotubes through an original method that allows limiting the mechanical degradation and oxidation of the carbon nanotubes by using a ball mill, while maintaining their good dispersion, so that the LFP precursor LFPs can be produced in very intimate contact with the carbon nanotubes. The carbon nanotubes are stabilized in the aqueous phase with alkali metal cations (such as sodium) of carboxymethylcellulose, and the LFP is directly synthesized on the carbon nanotubes. In this method, the use of water may lower the temperature required to obtain the desired olivine structure for the LFP, thus promoting good intercalation of the lithium. This novel approach makes it possible to reduce the size of the microconducting regions in the LFP. The optional additional step of coating the resulting composition with carbon may further significantly improve the conductive properties of the novel composition obtained using this method.
本發明係關於一種用於製備磷酸鐵鋰-碳組成物之方法，其包含下列步驟：
a) 製備重量比例在3%與5%之間的羧甲基纖維素之水溶液；
b) 在攪拌下，將量為該溶液之3重量%至5重量%的碳導入該溶液以獲得在該水和羧甲基纖維素中的碳分散液；
c) 在鹼性鋰鹽諸如氫氧化鋰之存在下，將該分散液轉移到垂直或水平球磨機之缽，以進行研磨持續90至150分鐘；
在步驟a)、b)及c)結束時獲得混合物A；
d) 將混合物A導入容納有水溶液(混合物B)之攪拌型反應器中，該水溶液含有鐵鹽(較佳是草酸鹽形式之鐵)及磷酸(其未經中和或經鋰部分中和，較佳是磷酸二氫鋰)，且鐵/磷莫耳比為1，其中混合物A和B所產生之鋰/鐵莫耳比是在1與1.1之間，碳之含量相對於A+B之和是在0.3重量%與10重量%之間，且鐵和磷之濃度是在0.05 M與5 M之間；
e) 關閉該反應器，然後在200℃及自生壓力下反應2小時；
f) 冷卻該反應器，接著藉由過濾收集該組成物、清洗及乾燥。
The present invention relates to a method for preparing lithium iron phosphate-carbon composition, which comprises the following steps:
a) preparing an aqueous solution of carboxymethyl cellulose in a weight ratio between 3% and 5%;
b) introducing carbon into the solution in an amount of 3% to 5% by weight of the solution under stirring to obtain a carbon dispersion in the water and carboxymethylcellulose;
c) transfer the dispersion to the bowl of a vertical or horizontal ball mill for grinding in the presence of an alkaline lithium salt such as lithium hydroxide for 90 to 150 minutes;
A mixture A is obtained at the end of steps a), b) and c);
d) Mixture A is introduced into a stirred reactor containing an aqueous solution (mixture B) containing an iron salt (preferably iron in the form of oxalate) and phosphoric acid (which is either unneutralized or partially neutralized with lithium , preferably lithium dihydrogen phosphate), and the iron/phosphorus molar ratio is 1, wherein the lithium/iron molar ratio produced by mixtures A and B is between 1 and 1.1, and the carbon content is relative to A+B the sum is between 0.3% and 10% by weight and the concentrations of iron and phosphorus are between 0.05M and 5M;
e) close the reactor, then react at 200°C and autogenous pressure for 2 hours;
f) Cool the reactor, then collect the composition by filtration, wash and dry.
在本發明之背景下，該碳可如組合或個別形式之石墨、碳纖維或碳奈米纖維(carbon nanofibre)(也已知為碳奈米原纖維(carbon nanofibril))、石墨烯或碳奈米管型。較佳地，彼為碳奈米管。這些係以粉末形式提供。
該等碳奈米管可為雙壁型碳奈米管(DWNT)或多壁型碳奈米管(MWNT)，較佳地，彼等為多壁型。根據本發明所用之碳奈米管一般具有範圍在0.4至100 nm，較佳0.4至50 nm，更佳1至30 nm，或甚至10至15 nm的平均直徑，且有利地具有0.1微米或更長，且有利地0.1至20微米，較佳地0.1至10微米之長度。這些較佳係以粉末形式提供。
該碳奈米管之長度/直徑比，或縱橫比，有利地是大於10且經常是大於100。其比表面積是例如在50與300 m
2/g之間，有利地在100與300 m
2/g之間，且其容積密度(bulk density)尤其可在0.01與0.5 g/cm
3之間，且更佳地在0.07與0.2 g/cm
3之間。該MWNT例如可包含5至25個壁或片，且更佳地7至20片。
該碳奈米管尤其是藉由化學蒸氣沉積(CVD)，例如根據在WO 06/082325中描述之方法獲得。根據專利申請案EP 1980530中的描述，彼等可得自可再生之原料，尤其是植物來源者。
碳奈米管之一實例可得自Arkema之商品名Graphistrength® C100。可將這些奈米管純化。
在該本發明之背景下，該LFP/CNT組成物含有在1重量%與10重量%之間，較佳在2重量%與5重量%之間的CNT。
這些碳奈米管在攪拌下被分散在羧甲基纖維素(CMC)之水溶液中，羧甲基纖維素的重量平均分子量可為50,000至150,000 g/mol，且較佳地在80,000與120,000 g/mol之間。
該溶液中之羧甲基纖維素的量是在2重量%與7重量%之間，較佳地在3重量%與5重量%之間。
該水/CMC/CNT溶液係在垂直或水平球磨機中持續進行處理90至150分鐘。該等球是具有1.2至1.6 mm之直徑範圍的氧化鋯類型之球，且轉子速度可從1500至2000 rpm。球磨機之使用限制應變，且藉由避免切割該等奈米管而令該等碳奈米管之整體性能被保留，這對LFP之良好的後續電連續性及更好的成長是有益的。在此步驟之期間，添加鹼性鋰鹽諸如氫氧化鋰。在一變化型中，也可能添加非離子性界面活性劑，例如具有8至12個聚氧伸乙基基團者。可使用之此種界面活性劑的一實例是Brij
TMS20。
在此步驟中所導入之鋰可為藉由本發明之方法所得之組成物中的總鋰量的至高99%。
所得之混合物的特徵在於藉由Mastersizer 3000所測得之大於1 μm之D50值及小於10μm之D99值。
該混合物在攪拌型反應器中與該LFP前驅物接觸。在裝填至該反應器之前，可以使用靜態混合器進行水/CMC/ CNT/鹼性鋰鹽與該磷/鋰/鐵混合物之混合操作。
這些前驅物係由鐵/磷之莫耳比為1之鐵(II)鹽(較佳是呈草酸鹽形式之鐵(II))及未經中和或經鋰部分中和之磷酸(較佳是磷酸二氫鋰)所組成。
這是以組成物成品中該鋰/鐵之莫耳比在1與1.1之間且較佳在1.02與1.08之間的方式完成。
同樣地，在該組成物成品中之碳奈米管的含量在0.3重量%與10重量%之間，較佳在0.5重量%與6重量%之間，且更佳在1重量%與5重量%之間。
在此反應器中，該鐵和磷之濃度是在0.05 M與5 M之間。
該反應器被關閉且在170與230℃之間，一般在200℃，以及自生壓力下進行反應以形成該LFP/碳奈米管組成物。
在此步驟結束時，該反應器被冷卻，且該LFP/CNT組成物被收集、過濾、清洗且乾燥。
本發明也關於使用本發明之方法所得之組成物。這些組成物的特徵在於鋰/鐵之莫耳比在1與1.1之間、鋰/磷之莫耳比為1，且碳奈米管之比例在0.3重量%與10重量%之間。
這些組成物後續以原樣或在陶瓷球磨機或空氣噴射磨機中進行研磨之後被使用於陰極的製造中。
這些經研磨或未經研磨之組成物可進行一個用於以一層碳覆蓋該組成物之粒子的額外步驟。
在此額外步驟中，該組成物被分散在含有10重量%與50重量%的糖(諸如葡萄糖)之溶液中。
在此額外步驟中，源自該糖之過量碳的重量代表該組成物重量的0.1重量%至5重量%的碳比例。
對該組成物和該糖溶液之分散液進行噴灑，接著乾燥，然後在300至700℃之溫度和惰性氣體環境下進行碳化以獲得經碳化粉末。在該碳化時，藉由所含之羧甲基纖維素所提供之過量碳是有利的。
接著使用陶瓷磨機或空氣噴射磨機研磨該粉末。在此額外步驟結束時所得的粉末組成物也形成本發明之範圍的一部分。
本發明之組成物具有大於150 mAh/g之電容量。
本發明也關於使用本發明之方法所產生之組成物所得的陰極和電池。
In the context of the present invention, the carbon may be, for example, graphite, carbon fibers or carbon nanofibres (also known as carbon nanofibrils), graphene or carbon nanotubes in combination or in individual form. type. Preferably, they are carbon nanotubes. These are available in powder form. The carbon nanotubes may be double-walled carbon nanotubes (DWNTs) or multi-walled carbon nanotubes (MWNTs), preferably, they are multi-walled. The carbon nanotubes used according to the invention generally have an average diameter in the range of 0.4 to 100 nm, preferably 0.4 to 50 nm, more preferably 1 to 30 nm, or even 10 to 15 nm, and advantageously have a diameter of 0.1 micron or more Long, and advantageously 0.1 to 20 microns, preferably 0.1 to 10 microns in length. These are preferably provided in powder form. The length/diameter ratio, or aspect ratio, of the carbon nanotubes is advantageously greater than 10 and often greater than 100. Its specific surface area is, for example, between 50 and 300 m 2 /g, advantageously between 100 and 300 m 2 /g, and its bulk density may especially be between 0.01 and 0.5 g/cm 3 , And more preferably between 0.07 and 0.2 g/cm 3 . The MWNT may for example comprise 5 to 25 walls or sheets, and more preferably 7 to 20 sheets. The carbon nanotubes are obtained in particular by chemical vapor deposition (CVD), for example according to the method described in WO 06/082325. According to the description in patent application EP 1980530, they are obtainable from renewable raw materials, especially those of plant origin. An example of carbon nanotubes is available from Arkema under the tradename Graphstrength® C100. These nanotubes can be purified. In the context of the present invention, the LFP/CNT composition contains between 1% and 10% by weight, preferably between 2% and 5% by weight of CNTs. These carbon nanotubes are dispersed in an aqueous solution of carboxymethylcellulose (CMC) under stirring. The weight average molecular weight of carboxymethylcellulose can be 50,000 to 150,000 g/mol, and preferably between 80,000 and 120,000 g /mol between. The amount of carboxymethylcellulose in the solution is between 2% and 7% by weight, preferably between 3% and 5% by weight. The water/CMC/CNT solution is continuously processed in a vertical or horizontal ball mill for 90 to 150 minutes. The balls are of the zirconia type with a diameter ranging from 1.2 to 1.6 mm and the rotor speed can be from 1500 to 2000 rpm. The use of a ball mill limits the strain and preserves the bulk properties of the carbon nanotubes by avoiding cutting the nanotubes, which is beneficial for good subsequent electrical continuity and better growth of LFP. During this step, a basic lithium salt such as lithium hydroxide is added. In a variant, it is also possible to add nonionic surfactants, for example those with 8 to 12 polyoxyethylene groups. An example of such a surfactant that can be used is Brij ™ S20. The lithium introduced in this step can be up to 99% of the total lithium in the composition obtained by the method of the present invention. The resulting mixture is characterized by a D50 value greater than 1 μm and a D99 value less than 10 μm measured by Mastersizer 3000. The mixture is contacted with the LFP precursor in a stirred reactor. The mixing operation of water/CMC/CNT/basic lithium salt and the phosphorus/lithium/iron mixture can be performed using a static mixer before loading into the reactor. These precursors consist of iron(II) salts with an iron/phosphorus molar ratio of 1 (preferably iron(II) in the oxalate form) and unneutralized or lithium partially neutralized phosphoric acid (more Preferably it is composed of lithium dihydrogen phosphate). This is done in such a way that the lithium/iron molar ratio in the finished composition is between 1 and 1.1 and preferably between 1.02 and 1.08. Likewise, the content of carbon nanotubes in the finished composition is between 0.3% by weight and 10% by weight, preferably between 0.5% by weight and 6% by weight, and more preferably between 1% by weight and 5% by weight %between. In this reactor, the iron and phosphorus concentrations were between 0.05M and 5M. The reactor is closed and the reaction is performed between 170 and 230° C., typically 200° C., and autogenous pressure to form the LFP/carbon nanotube composition. At the end of this step, the reactor was cooled, and the LFP/CNT composition was collected, filtered, washed and dried. The invention also relates to compositions obtained using the method of the invention. These compositions are characterized by a lithium/iron molar ratio between 1 and 1.1, a lithium/phosphorous molar ratio of 1, and a carbon nanotube ratio between 0.3% and 10% by weight. These compositions are subsequently used in the manufacture of cathodes as such or after grinding in ceramic ball mills or air jet mills. These ground or unground compositions can be subjected to an additional step for covering the particles of the composition with a layer of carbon. In this additional step, the composition is dispersed in a solution containing 10% and 50% by weight of sugar, such as glucose. In this additional step, the weight of excess carbon derived from the sugar represents a carbon proportion of 0.1% to 5% by weight of the composition. The dispersion of the composition and the sugar solution is sprayed, followed by drying, and then carbonized at a temperature of 300 to 700° C. under an inert gas atmosphere to obtain carbonized powder. In this carbonization, the excess carbon provided by the contained carboxymethylcellulose is advantageous. The powder is then ground using a ceramic mill or an air jet mill. The powder composition obtained at the end of this additional step also forms part of the scope of the present invention. The composition of the present invention has a capacitance greater than 150 mAh/g. The invention also relates to cathodes and batteries obtained using compositions produced by the method of the invention.