JP7494647B2 - Positive electrodes for lithium-ion secondary batteries - Google Patents
Positive electrodes for lithium-ion secondary batteries Download PDFInfo
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- JP7494647B2 JP7494647B2 JP2020140658A JP2020140658A JP7494647B2 JP 7494647 B2 JP7494647 B2 JP 7494647B2 JP 2020140658 A JP2020140658 A JP 2020140658A JP 2020140658 A JP2020140658 A JP 2020140658A JP 7494647 B2 JP7494647 B2 JP 7494647B2
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims description 28
- 229910001416 lithium ion Inorganic materials 0.000 title claims description 28
- 239000002245 particle Substances 0.000 claims description 221
- DVATZODUVBMYHN-UHFFFAOYSA-K lithium;iron(2+);manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[Fe+2].[O-]P([O-])([O-])=O DVATZODUVBMYHN-UHFFFAOYSA-K 0.000 claims description 27
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 26
- 229910052596 spinel Inorganic materials 0.000 claims description 21
- 239000011029 spinel Substances 0.000 claims description 21
- 229910052799 carbon Inorganic materials 0.000 claims description 19
- 229910021450 lithium metal oxide Inorganic materials 0.000 claims description 17
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 16
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 10
- 229910052748 manganese Inorganic materials 0.000 claims description 10
- 239000011572 manganese Substances 0.000 claims description 10
- 229910052742 iron Inorganic materials 0.000 claims description 9
- 239000000203 mixture Substances 0.000 description 18
- 238000000034 method Methods 0.000 description 17
- 239000007774 positive electrode material Substances 0.000 description 17
- 239000011149 active material Substances 0.000 description 12
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- 229910052744 lithium Inorganic materials 0.000 description 6
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- VLXXBCXTUVRROQ-UHFFFAOYSA-N lithium;oxido-oxo-(oxomanganiooxy)manganese Chemical compound [Li+].[O-][Mn](=O)O[Mn]=O VLXXBCXTUVRROQ-UHFFFAOYSA-N 0.000 description 6
- 239000000463 material Substances 0.000 description 6
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 5
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- SURQXAFEQWPFPV-UHFFFAOYSA-L iron(2+) sulfate heptahydrate Chemical compound O.O.O.O.O.O.O.[Fe+2].[O-]S([O-])(=O)=O SURQXAFEQWPFPV-UHFFFAOYSA-L 0.000 description 4
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 4
- ISPYRSDWRDQNSW-UHFFFAOYSA-L manganese(II) sulfate monohydrate Chemical compound O.[Mn+2].[O-]S([O-])(=O)=O ISPYRSDWRDQNSW-UHFFFAOYSA-L 0.000 description 4
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- JIPBPJZISZCBJQ-UHFFFAOYSA-N 1-[(2-methylpropan-2-yl)oxycarbonyl]-3-(pyridin-4-ylmethyl)piperidine-3-carboxylic acid Chemical compound C1N(C(=O)OC(C)(C)C)CCCC1(C(O)=O)CC1=CC=NC=C1 JIPBPJZISZCBJQ-UHFFFAOYSA-N 0.000 description 2
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- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 2
- 238000001479 atomic absorption spectroscopy Methods 0.000 description 2
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- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Chemical compound [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 description 2
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- 229920000049 Carbon (fiber) Polymers 0.000 description 1
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- 229920006369 KF polymer Polymers 0.000 description 1
- 229910015645 LiMn Inorganic materials 0.000 description 1
- 229910015643 LiMn 2 O 4 Inorganic materials 0.000 description 1
- 229910015944 LiMn0.8Fe0.2PO4 Inorganic materials 0.000 description 1
- 229910016145 LiMn1 Inorganic materials 0.000 description 1
- 229910002991 LiNi0.5Co0.2Mn0.3O2 Inorganic materials 0.000 description 1
- 229910013870 LiPF 6 Inorganic materials 0.000 description 1
- 229910001290 LiPF6 Inorganic materials 0.000 description 1
- 229910002097 Lithium manganese(III,IV) oxide Inorganic materials 0.000 description 1
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- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
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- PQVSTLUFSYVLTO-UHFFFAOYSA-N ethyl n-ethoxycarbonylcarbamate Chemical compound CCOC(=O)NC(=O)OCC PQVSTLUFSYVLTO-UHFFFAOYSA-N 0.000 description 1
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- ILXAVRFGLBYNEJ-UHFFFAOYSA-K lithium;manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[O-]P([O-])([O-])=O ILXAVRFGLBYNEJ-UHFFFAOYSA-K 0.000 description 1
- 230000007257 malfunction Effects 0.000 description 1
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
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Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Battery Electrode And Active Subsutance (AREA)
Description
本発明は、リチウムイオン二次電池用正極に関するものである。 The present invention relates to a positive electrode for a lithium-ion secondary battery.
リチウムイオン二次電池は、高いエネルギー密度を有し、出力特性に優れる反面、不具合が生じると貯蔵されているエネルギーが短時間に放出され、電池が発火・炎上する危険性がある。そのためリチウムイオン二次電池にとっては、出力特性の向上とともに、安全性の向上が重要な課題である。 Lithium-ion secondary batteries have high energy density and excellent output characteristics, but if a malfunction occurs, the stored energy is released in a short time, and there is a risk that the battery may catch fire or burst into flames. Therefore, improving safety, along with improving output characteristics, is an important issue for lithium-ion secondary batteries.
リチウムイオン二次電池の安全性を大きく左右するのが正極活物質であることはよく知られている。電気自動車向け等の大型電池で用いられることが多いスピネル系マンガン酸リチウム正極活物質は、比較的安価であり、出力特性に優れた正極活物質であるが、高温条件下においてマンガンが溶出することや、過充電による酸素の放出を伴う結晶構造の変化に起因して劣化が促進され、過充電の程度によっては発煙・発火に至る危険性があるなど、安全性に課題がある。 It is well known that the safety of lithium-ion secondary batteries is largely determined by the positive electrode active material. Spinel-type lithium manganese oxide positive electrode active material, which is often used in large batteries for electric vehicles and other applications, is relatively inexpensive and has excellent output characteristics. However, it has safety issues, such as manganese leaching under high temperature conditions, accelerated deterioration due to changes in crystal structure accompanied by oxygen release due to overcharging, and the risk of smoke and fire depending on the degree of overcharging.
一方で、定置用電池などに用いられることが多いリン酸鉄リチウムなどのオリビン系正極活物質は、酸素がリンと共有結合しているために容易には酸素を放出せず、高温条件下においても比較的安定である安全性の高い正極材料であることが知られている。 On the other hand, olivine-based positive electrode active materials such as lithium iron phosphate, which are often used in stationary batteries, do not release oxygen easily because oxygen is covalently bonded to phosphorus, and are known to be relatively stable and safe even under high temperature conditions.
そこで、これらの正極活物質を組み合わせ、高い出力特性と安全性を両立することが検討されている。例えば、正極集電体および前記正極集電体上に形成されてなる正極活物質を含む正極と、負極集電体および前記負極集電体上に形成されてなる負極活物質を含む負極と、を含むリチウムイオン二次電池用電極であって、前記負極活物質は、黒鉛であり、前記正極活物質は、複合マンガン酸リチウムおよびオリビン型複合燐酸鉄リチウムであり、前記複合マンガン酸リチウムの含有量が、前記オリビン型複合燐酸鉄リチウムと前記複合マンガン酸リチウムの総量に対して30質量%以下である、リチウムイオン二次電池用電極(例えば、特許文献1参照)、オリビン型構造のリチウム含有リン酸化合物と、スピネル型構造のマンガン酸リチウムとを含む、正極活物質(例えば、特許文献2参照)、リチウムイオンの挿入脱離が可能であるとともに、前記リチウムイオンの輸送を媒介する電解液に浸漬される正極及び負極を有する二次電池であって、前記正極は、第1の正極材料と第2の正極材料とを含み、前記第1の正極材料は、リチウムマンガン酸化物(LiMn2-XMXO4,M=Li、Fe、Co、Ni、Al、Mg)であり、前記第2の正極材料は、LiMn1-XMXPO4(M=Fe、Co、Ni,0≦X≦1)である二次電池(例えば、特許文献3参照)などが提案されている。 Therefore, studies are being conducted to combine these positive electrode active materials to achieve both high output characteristics and safety. For example, there is an electrode for a lithium ion secondary battery including a positive electrode including a positive electrode current collector and a positive electrode active material formed on the positive electrode current collector, and a negative electrode including a negative electrode current collector and a negative electrode active material formed on the negative electrode current collector, the negative electrode active material being graphite, the positive electrode active material being a composite lithium manganese oxide and an olivine-type composite lithium iron phosphate, and the content of the composite lithium manganese oxide is 30 mass % or less with respect to the total amount of the olivine-type composite lithium iron phosphate and the composite lithium manganese oxide (see, for example, Patent Document 1); a positive electrode active material including a lithium-containing phosphate compound having an olivine structure and a lithium manganese oxide having a spinel structure (see, for example, Patent Document 2); and a secondary battery having a positive electrode and a negative electrode that are capable of inserting and removing lithium ions and are immersed in an electrolyte that mediates the transport of the lithium ions, the positive electrode including a first positive electrode material and a second positive electrode material, the first positive electrode material being lithium manganese oxide (LiMn 2- XMxO4 , M = Li, Fe, Co, Ni, Al , Mg) and the second positive electrode material is LiMn1 - XMxPO4 (M = Fe, Co, Ni, 0 < X < 1) (see, for example, Patent Document 3).
リン酸鉄リチウム、リン酸マンガン鉄リチウム、リン酸マンガンリチウムなどのオリビン系正極活物質は、スピネル系正極活物質と比べて過充電に対する耐性が強いことが知られている。特許文献1~3に記載されるように、電気抵抗が大きいオリビン系正極活物質をスピネル系正極活物質と混合することにより、リチウムイオン二次電池に対して通常よりも著しく大きな外部電圧がかかった状態、すなわち過充電状態において、スピネル系正極活物質に流れる電流を軽減することができる。これは、リチウムイオン二次電池の正負極間の過充電時にかかる電圧V過充電にオームの法則(I=V/R)をそのまま当てはめると、過充電時に流れる電流の大きさが内部抵抗に反比例することから説明される。しかしながら、特許文献1~2に開示された電極は、出力特性が不十分である課題があり、特許文献3に開示された電極は、過充電耐性が不十分である課題があった。 It is known that olivine-based positive electrode active materials such as lithium iron phosphate, lithium manganese iron phosphate, and lithium manganese phosphate have a stronger resistance to overcharging than spinel-based positive electrode active materials. As described in Patent Documents 1 to 3, by mixing an olivine-based positive electrode active material having a large electrical resistance with a spinel-based positive electrode active material, it is possible to reduce the current flowing through the spinel-based positive electrode active material in a state in which a significantly larger external voltage than normal is applied to the lithium-ion secondary battery, i.e., in an overcharged state. This is explained by the fact that, when Ohm's law (I=V/R) is directly applied to the voltage V overcharge applied between the positive and negative electrodes of a lithium-ion secondary battery during overcharging, the magnitude of the current flowing during overcharging is inversely proportional to the internal resistance. However, the electrodes disclosed in Patent Documents 1 and 2 have a problem of insufficient output characteristics, and the electrode disclosed in Patent Document 3 has a problem of insufficient overcharge resistance.
かかる課題に鑑み、本発明の目的は、出力特性が高く、過充電耐性に優れたリチウムイオン二次電池用正極を提供することである。 In view of these problems, the object of the present invention is to provide a positive electrode for a lithium-ion secondary battery that has high output characteristics and excellent overcharge resistance.
上記の課題を解決するため、本発明は、主として以下の構成を有する。
スピネル系リチウム金属酸化物粒子およびリン酸マンガン鉄リチウム粒子を含有するリチウムイオン二次電池用正極であって、
リン酸マンガン鉄リチウム粒子の粒子径に対するスピネル系リチウム金属酸化物粒子の粒子径の比(スピネル系リチウム金属酸化物粒子の粒子径/リン酸マンガン鉄リチウム粒子の粒子径)が2.0以上10.0以下であり、
リン酸マンガン鉄リチウム粒子の含有量に対するスピネル系リチウム金属酸化物粒子の含有量の重量比(スピネル系リチウム金属酸化物粒子の含有量/リン酸マンガン鉄リチウム粒子の含有量)が1.0以上4.0以下である、リチウムイオン二次電池用正極。
In order to solve the above problems, the present invention mainly has the following configuration.
A positive electrode for a lithium ion secondary battery containing spinel-based lithium metal oxide particles and lithium manganese iron phosphate particles,
a ratio of a particle size of the spinel-based lithium metal oxide particles to a particle size of the lithium manganese iron phosphate particles (particle size of the spinel-based lithium metal oxide particles/particle size of the lithium manganese iron phosphate particles) is 2.0 or more and 10.0 or less;
A positive electrode for a lithium ion secondary battery, in which a weight ratio of a content of spinel-based lithium metal oxide particles to a content of lithium manganese iron phosphate particles (content of spinel-based lithium metal oxide particles/content of lithium manganese iron phosphate particles) is 1.0 or more and 4.0 or less.
本発明のリチウムイオン二次電池用正極を用いることにより、出力特性が高く、さらに過充電耐性に優れたリチウムイオン二次電池を得ることができる。 By using the positive electrode for a lithium-ion secondary battery of the present invention, a lithium-ion secondary battery with high output characteristics and excellent overcharge resistance can be obtained.
本発明のリチウムイオン二次電池用正極(以下、単に「正極」という場合がある)は、LiMn2O4で表されるスピネル系リチウム金属酸化物粒子およびLiαMnaFebPO4(0.9≦α≦1.1、0<a≦1、0<b≦1、0.9≦a+b≦1.1)で表されるリン酸マンガン鉄リチウム粒子を含有する。前述のとおり、スピネル系リチウム金属酸化物(以下、LMOと略す場合がある)粒子は出力特性に優れ、リン酸マンガン鉄リチウム(以下、LMFPと略す場合がある)粒子は過充電耐性に優れる。スピネル系リチウム金属酸化物粒子およびリン酸マンガン鉄リチウム粒子は、その製造条件によりそれぞれ粒子径を変化させることができるが、本発明者らの検討により、リン酸マンガン鉄リチウム粒子の粒子径に対するスピネル系リチウム金属酸化物粒子の粒子径の比(スピネル系リチウム金属酸化物粒子の粒子径/リン酸マンガン鉄リチウム粒子の粒子径)が2.0以上10.0以下であり、リン酸マンガン鉄リチウム粒子の含有量に対するスピネル系リチウム金属酸化物粒子の含有量の重量比(スピネル系リチウム金属酸化物粒子の含有量/リン酸マンガン鉄リチウム粒子の含有量)が1.0以上4.0以下である場合において、出力特性と過充電耐性が両立できることを見出した。 The positive electrode for lithium ion secondary battery of the present invention (hereinafter sometimes simply referred to as "positive electrode") contains spinel-based lithium metal oxide particles represented by LiMn2O4 and lithium manganese iron phosphate particles represented by LiαMnαFebPO4 (0.9≦α ≦ 1.1 , 0<a≦1, 0<b≦1, 0.9≦a+b≦1.1). As described above, the spinel-based lithium metal oxide (hereinafter sometimes abbreviated as LMO) particles have excellent output characteristics, and the lithium manganese iron phosphate (hereinafter sometimes abbreviated as LMFP) particles have excellent overcharge resistance. The particle size of the spinel-based lithium metal oxide particles and the lithium manganese iron phosphate particles can be changed depending on the production conditions, but the inventors have found through their investigations that when the ratio of the particle size of the spinel-based lithium metal oxide particles to the particle size of the lithium manganese iron phosphate particles (particle size of spinel-based lithium metal oxide particles/particle size of lithium manganese iron phosphate particles) is 2.0 or more and 10.0 or less, and the weight ratio of the content of the spinel-based lithium metal oxide particles to the content of the lithium manganese iron phosphate particles (content of spinel-based lithium metal oxide particles/content of lithium manganese iron phosphate particles) is 1.0 or more and 4.0 or less, output characteristics and overcharge resistance can be achieved simultaneously.
なお、本発明の正極は、LMO粒子、LMFP粒子とともに、その他の活物質粒子を含有してもよい。 The positive electrode of the present invention may contain other active material particles in addition to the LMO particles and LMFP particles.
本明細書におけるLMFPとは、LiαMnaFebPO4において、0.9≦α≦1.1、0<a≦1、0<b≦1、0.9≦a+b≦1.1を満たす化合物を指す。ただし、ドーピング元素として、上記以外の元素が0.1重量%以上10重量%以下の範囲で添加されている場合にも、本発明におけるLMFPに含めるものとする。 In this specification , LMFP refers to a compound that satisfies 0.9≦α≦1.1 , 0<a≦1, 0 <b≦1, and 0.9≦a+b≦1.1 in LiαMnαFebPO4 . However, even if an element other than the above is added as a doping element in a range of 0.1% by weight to 10% by weight, it is also included in the LMFP of the present invention.
LMFPにおいて、マンガン比率aが大きく、鉄比率bが小さいほど、理論的にはエネルギー密度は高まる一方、電子伝導性とイオン伝導性が低下する。本発明において、aの値は、LMFP粒子の体積抵抗率をより大きくして過充電耐性をより向上させる観点から、0.6以上が好ましく、0.75以上がより好ましい。一方、aの値は、サイクル耐性を向上する観点から、0.9以下が好ましく、0.85以下がより好ましい。 In LMFP, the greater the manganese ratio a and the smaller the iron ratio b, the higher the energy density theoretically becomes, while the electronic conductivity and ionic conductivity decrease. In the present invention, the value of a is preferably 0.6 or more, and more preferably 0.75 or more, from the viewpoint of increasing the volume resistivity of the LMFP particles and further improving the overcharge resistance. On the other hand, the value of a is preferably 0.9 or less, and more preferably 0.85 or less, from the viewpoint of improving the cycle resistance.
ここで、LMFPの組成は、リチウムについては原子吸光分析、マンガン、鉄、リンについてはICP発光分析法により特定することができる。前記式α、a、bについては小数点以下第3位まで測定し、四捨五入にて小数点以下第2位までを採用する。ただし、小数点以下第2位が0の場合は小数点以下第1位まで表記する。また、LMFP製造時の原料仕込み比が既知である場合は、その仕込み比から組成を求めることができる。 The composition of LMFP can be determined by atomic absorption spectrometry for lithium, and ICP emission spectrometry for manganese, iron, and phosphorus. The formulas α, a, and b are measured to three decimal places and rounded off to the second decimal place. However, if the second decimal place is 0, the value is expressed to the first decimal place. In addition, if the raw material charge ratio during LMFP production is known, the composition can be determined from that charge ratio.
LMFP粒子は、表面に炭素層を有することが好ましく、表面全体にわたって均一に炭素層を有することがより好ましい。炭素層を有することにより、LMFP粒子を全体にわたって均一に電子伝導性を向上させることができる。LMFP粒子中における炭素層の含有量は、電子伝導性をより向上させて出力特性をより向上させる観点から、1重量%以上が好ましい。一方、LMFP粒子中における炭素層の含有量は、炭素層とLMFPとの副反応を抑制して出力特性をより向上させる観点から、6重量%以下が好ましい。 The LMFP particles preferably have a carbon layer on the surface, and more preferably have a carbon layer uniformly over the entire surface. By having a carbon layer, the electronic conductivity of the LMFP particles can be improved uniformly over the entire surface. The content of the carbon layer in the LMFP particles is preferably 1 wt % or more from the viewpoint of further improving the electronic conductivity and further improving the output characteristics. On the other hand, the content of the carbon layer in the LMFP particles is preferably 6 wt % or less from the viewpoint of suppressing side reactions between the carbon layer and LMFP and further improving the output characteristics.
ここで、LMFP粒子の炭素層の含有量は、例えば、炭素・硫黄同時定量分析装置EMIA-920V(株式会社堀場製作所製)を用いて測定することができる。 Here, the carbon layer content of the LMFP particles can be measured, for example, using a carbon/sulfur simultaneous quantitative analyzer EMIA-920V (manufactured by Horiba, Ltd.).
LMFP粒子の粒子径は、後述する正極の製造方法におけるペーストの取り扱い性の観点から、3μm以上が好ましい。一方、LMFP粒子の粒子径は、後述する合剤層の厚みとの関係から、40μm以下が好ましい。LMFP粒子の粒子径とは、正極中に存在する粒子が造粒体である場合は2次粒子の、造粒体ではない場合は1次粒子の粒径の算術平均値を指す。 The particle diameter of the LMFP particles is preferably 3 μm or more from the viewpoint of the handleability of the paste in the manufacturing method of the positive electrode described later. On the other hand, the particle diameter of the LMFP particles is preferably 40 μm or less from the viewpoint of the thickness of the mixture layer described later. The particle diameter of the LMFP particles refers to the arithmetic mean value of the particle diameter of the secondary particles when the particles present in the positive electrode are granules, and the arithmetic mean value of the particle diameter of the primary particles when the particles are not granules.
本発明におけるLMFP粒子の体積抵抗率ρ(Ω・cm)は、102≦ρ≦106が好ましい。正極の安全性を向上させるためには、正極の抵抗を低減させることにより短絡時など異常時の電流から発生するジュール熱を抑える方法と、正極の抵抗を高くすることにより異常時の電流値そのものを低減する方法がある。LMO粒子の過充電耐性を向上させるためには後者の方が有効であり、LMFP粒子の抵抗が高いことが好ましい。そのため、本発明におけるLMFP粒子の体積抵抗率は102(Ω・cm)以上が好ましく、103(Ω・cm)以上がより好ましい。一方、LMFP粒子の体積抵抗率が106(Ω・cm)以下であると、LMFP粒子の出力特性をより高く維持することができる。ここで、LMFPの体積抵抗率は、正極中のLMFP粒子について、例えば、粉体抵抗測定システムMCP-PD51(株式会社三菱ケミカルアナリテック製)を用いて、25MPa条件下において測定することができる。正極からLMFP粒子を取り出す方法としては、例えば、正極の集電体から合剤層を剥離した後、N-メチルピロリジノン等の有機溶剤によりバインダーを、希塩酸によりLMO粒子をそれぞれ溶解させ、残ったLFMP粒子を乾燥する方法などが挙げられる。さらにカーボンブラックなどの導電助剤を含有する場合には、バインダーおよびLMO粒子を溶解させて残った固体から、遠心分離により比重の小さいカーボンブラックを除去し、得られたLFMP粒子を乾燥する方法などが挙げられる。また、正極製造時の原料としてのLMFP粒子について、同様に体積抵抗率を測定してもよい。 The volume resistivity ρ (Ω·cm) of the LMFP particles in the present invention is preferably 10 2 ≦ρ≦10 6. In order to improve the safety of the positive electrode, there is a method of suppressing Joule heat generated from current in an abnormal state such as a short circuit by reducing the resistance of the positive electrode, and a method of reducing the current value itself in an abnormal state by increasing the resistance of the positive electrode. The latter is more effective in improving the overcharge resistance of the LMO particles, and it is preferable that the resistance of the LMFP particles is high. Therefore, the volume resistivity of the LMFP particles in the present invention is preferably 10 2 (Ω·cm) or more, more preferably 10 3 (Ω·cm) or more. On the other hand, if the volume resistivity of the LMFP particles is 10 6 (Ω·cm) or less, the output characteristics of the LMFP particles can be maintained at a higher level. Here, the volume resistivity of the LMFP can be measured for the LMFP particles in the positive electrode under a condition of 25 MPa, for example, using a powder resistance measurement system MCP-PD51 (manufactured by Mitsubishi Chemical Analytech Co., Ltd.). As a method for extracting LMFP particles from a positive electrode, for example, after peeling off the mixture layer from the current collector of the positive electrode, the binder is dissolved with an organic solvent such as N-methylpyrrolidinone, and the LMO particles are dissolved with dilute hydrochloric acid, and the remaining LFMP particles are dried. In addition, when a conductive assistant such as carbon black is contained, a method of removing carbon black having a small specific gravity from the remaining solid after dissolving the binder and LMO particles by centrifugation, and drying the obtained LFMP particles, etc. may be mentioned. In addition, the volume resistivity of the LMFP particles as a raw material in the production of the positive electrode may be measured in the same manner.
なお、LMFPの体積抵抗率は、マンガンと鉄の比率や、1次粒子径や、例えば炭素層を有するLMFPの場合、炭素層含有量や焼成温度などの炭素被覆条件によって、所望の範囲に調整することができる。 The volume resistivity of the LMFP can be adjusted to a desired range by adjusting the ratio of manganese to iron, the primary particle size, and, in the case of an LMFP having a carbon layer, the carbon layer content, the firing temperature, and other carbon coating conditions.
本明細書におけるLMOとは、LiMn2O4で表される化合物を指す。ただし、ドーピング元素として、上記以外の元素が0.1重量%以上10重量%以下の範囲で添加されている場合にも、本発明におけるLMOにそれぞれ含めるものとする。 In this specification, LMO refers to a compound represented by LiMn 2 O 4. However, even when an element other than the above is added as a doping element in a range of 0.1 wt % to 10 wt %, it is also included in the LMO of the present invention.
ここで、LMOの組成は、リチウムについては原子吸光分析、マンガンについてはICP発光分析法により特定することができる。 Here, the composition of LMO can be determined by atomic absorption spectrometry for lithium and ICP optical emission spectrometry for manganese.
LMO粒子の粒子径は、後述する正極の製造方法におけるペーストの取り扱い性の観点から、3μm以上が好ましい。一方、LMO粒子の粒子径は、後述する合剤層の厚みとの関係から、40μm以下が好ましい。LMO粒子の粒子径とは、正極中に存在する粒子が造粒体である場合は2次粒子の、造粒体ではない場合は1次粒子の粒径の算術平均値を指す。 The particle diameter of the LMO particles is preferably 3 μm or more from the viewpoint of the ease of handling of the paste in the manufacturing method of the positive electrode described later. On the other hand, the particle diameter of the LMO particles is preferably 40 μm or less from the viewpoint of the thickness of the mixture layer described later. The particle diameter of the LMO particles refers to the arithmetic mean value of the particle diameter of the secondary particles when the particles present in the positive electrode are granules, and the arithmetic mean value of the particle diameter of the primary particles when the particles are not granules.
本発明においては、LMFP粒子の粒子径に対するLMO粒子の粒子径の比(LMO粒子の粒子径/LMFP粒子の粒子径)が2.0以上10.0以下である。前述のとおり、LMO粒子は出力特性に優れる一方で過充電耐性が低く、LMFP粒子は過充電耐性に優れる一方で出力特性が低いが、本発明においては、LMO粒子間の空隙に電気抵抗の大きいLMFP粒子を充填することにより、過充電状態においてLMO粒子に流れる電流を抑制し、過充電耐性を向上させることができる。前記粒子径の比が2.0よりも小さいと、正極内においてLMO粒子間の空隙にLMFP粒子が十分に充填されず、LMO粒子同士の接触により過充電耐性が劣化する。一方、前記粒子径の比が10.0よりも大きい場合、LMFP粒子の粒子径が小さいためにLMFPの比表面積が大きくなり、過充電状態においてで電解液とLMFP粒子との間で不可逆的な化学反応が促進され、過充電耐性およびサイクル耐性が低下する。 In the present invention, the ratio of the particle diameter of the LMO particles to the particle diameter of the LMFP particles (particle diameter of the LMO particles/particle diameter of the LMFP particles) is 2.0 or more and 10.0 or less. As described above, the LMO particles have excellent output characteristics but low overcharge resistance, and the LMFP particles have excellent overcharge resistance but low output characteristics. In the present invention, the voids between the LMO particles are filled with LMFP particles having high electrical resistance, thereby suppressing the current flowing through the LMO particles in an overcharged state and improving the overcharge resistance. If the particle diameter ratio is less than 2.0, the voids between the LMO particles in the positive electrode are not sufficiently filled with LMFP particles, and the overcharge resistance is deteriorated due to contact between the LMO particles. On the other hand, when the particle size ratio is greater than 10.0, the particle size of the LMFP particles is small, so the specific surface area of the LMFP becomes large, and irreversible chemical reactions between the electrolyte and the LMFP particles in an overcharged state are promoted, resulting in reduced overcharge resistance and cycle resistance.
ここで、LMFP粒子およびLMO粒子の粒子径とは、正極中に存在する各粒子、すなわち、造粒体である場合は2次粒子の、造粒体ではない場合は1次粒子の、粒径の算術平均値を指し、走査型電子顕微鏡を用いて測定することができる。具体的には、走査型電子顕微鏡を用いて、正極を倍率3,000倍にて拡大観察し、無作為に選択した粒子について粒径を測定する。このとき、粒子が球形でない場合は、2次元像において測定できる長軸と短軸の平均値をその粒径とする。また、その粒子について、エネルギー分散型X線分光法を用いて組成分析を行い、LMFP粒子とLMO粒子に分類する。同様の操作を繰り返してLMFP粒子およびLMO粒子の各100個の粒径を測定し、それぞれの数平均値を算出することにより、各粒子の粒子径を求めることができる。また、正極製造時の原料としてのLMFP粒子およびLMO粒子について、走査型電子顕微鏡を用いて同様に粒子径を測定してもよい。 Here, the particle size of the LMFP particles and the LMO particles refers to the arithmetic mean value of the particle size of each particle present in the positive electrode, that is, the secondary particles in the case of granules, and the primary particles in the case of non-granules, and can be measured using a scanning electron microscope. Specifically, the positive electrode is observed at a magnification of 3,000 times using a scanning electron microscope, and the particle size of randomly selected particles is measured. At this time, if the particle is not spherical, the average value of the major axis and minor axis that can be measured in the two-dimensional image is taken as the particle size. In addition, the particle is subjected to composition analysis using energy dispersive X-ray spectroscopy, and classified into LMFP particles and LMO particles. The same operation is repeated to measure the particle size of 100 LMFP particles and LMO particles, and the number average value of each is calculated, thereby obtaining the particle size of each particle. In addition, the particle size of LMFP particles and LMO particles as raw materials during the production of the positive electrode may be measured in the same manner using a scanning electron microscope.
LMFP粒子およびLMO粒子の粒子径は、例えば、後述するLMFP粒子およびLMO粒子の製造方法において、スプレードライヤーを用い、原料となるLMFP水分散液およびLMO水分散液の重量濃度を変化させることにより、所望の範囲に容易に調整することができる。 The particle size of the LMFP particles and LMO particles can be easily adjusted to the desired range, for example, by using a spray dryer to change the weight concentration of the raw material LMFP aqueous dispersion and LMO aqueous dispersion in the manufacturing method of LMFP particles and LMO particles described below.
本発明においては、LMFP粒子の含有量に対するLMO粒子の含有量の重量比(LMO粒子の含有量/LMFP粒子の含有量)が1.0以上4.0以下である。前述のとおり、LMO粒子は出力特性に優れる一方で過充電耐性が低く、LMFP粒子は過充電耐性に優れる一方で出力特性が低いため、前記重量比が1.0よりも小さい場合、LMO粒子が相対的に少なくなり、出力特性が低下する。一方、前記重量比が4.0を超えると、過充電耐性が低下する。 In the present invention, the weight ratio of the LMO particle content to the LMFP particle content (LMO particle content/LMFP particle content) is 1.0 or more and 4.0 or less. As described above, LMO particles have excellent output characteristics but low overcharge resistance, and LMFP particles have excellent overcharge resistance but low output characteristics, so when the weight ratio is less than 1.0, the LMO particles become relatively scarce and the output characteristics deteriorate. On the other hand, when the weight ratio exceeds 4.0, the overcharge resistance deteriorates.
ここで、正極内におけるLMFP粒子およびLMO粒子の含有量比は、リチウムイオン電池の正極を集電体から剥離した後、LMFP粒子およびLMO粒子について粉末X線回折測定を行い、得られた結果にリートベルト解析を施すことにより求めることができる。また、正極製造時の原料としてのLMFP粒子およびLMO粒子の仕込み比が既知である場合は、その仕込み比から含有量比を求めることができる。 Here, the content ratio of LMFP particles and LMO particles in the positive electrode can be determined by peeling the positive electrode of the lithium ion battery from the current collector, performing powder X-ray diffraction measurement on the LMFP particles and LMO particles, and applying Rietveld analysis to the obtained results. In addition, if the charge ratio of LMFP particles and LMO particles as raw materials in manufacturing the positive electrode is known, the content ratio can be determined from the charge ratio.
本発明の正極が、LMO粒子、LMFP粒子とともに、その他の活物質粒子を含有する場合、LMFP粒子とLMO粒子による効果をより向上させる観点から、その他の活物質粒子の含有量は、全活物質粒子(LMO粒子、LMFP粒子、その他の活物質粒子の合計)中、30重量%以下が好ましい。 When the positive electrode of the present invention contains other active material particles in addition to LMO particles and LMFP particles, from the viewpoint of further improving the effects of the LMFP particles and LMO particles, the content of the other active material particles is preferably 30% by weight or less of the total active material particles (the sum of the LMO particles, LMFP particles, and other active material particles).
ここで、正極内におけるその他の活物質粒子の含有量は、LMFP粒子やLMO粒子の含有量と同様に求めることができる。 Here, the content of other active material particles in the positive electrode can be determined in the same manner as the content of LMFP particles and LMO particles.
本発明の正極は、アルミ箔などの集電体上に、LMFP粒子およびLMO粒子とともに、バインダーや導電助剤などの添加剤を含有する合剤層を有することが好ましい。 The positive electrode of the present invention preferably has a mixture layer containing LMFP particles and LMO particles as well as additives such as a binder and a conductive assistant on a current collector such as aluminum foil.
バインダーとしては、例えば、ポリフッ化ビニルデン、スチレンブタジエンゴムなどが挙げられる。これらを2種以上含有してもよい。 Examples of binders include polyvinylidene fluoride and styrene-butadiene rubber. Two or more of these may be included.
正極合剤層中におけるバインダーの含有量は、0.3重量%以上10重量%以下が好ましい。バインダーの含有量を0.3重量%以上とすることにより、バインダーの結着効果により、塗膜を形成した場合に塗膜形状を容易に維持することができる。一方、バインダーの含有量を10重量%以下とすることにより、正極内の抵抗の増加を抑制することができる。 The binder content in the positive electrode mixture layer is preferably 0.3% by weight or more and 10% by weight or less. By making the binder content 0.3% by weight or more, the binding effect of the binder makes it easy to maintain the shape of the coating film when it is formed. On the other hand, by making the binder content 10% by weight or less, it is possible to suppress an increase in resistance in the positive electrode.
導電助剤としては、例えば、アセチレンブラック、ケッチェンブラック、カーボンファイバー、カーボンナノチューブなどが挙げられる。これらを2種以上含有してもよい。 Examples of conductive additives include acetylene black, ketjen black, carbon fiber, and carbon nanotubes. Two or more of these may be included.
合剤層中における導電助剤の含有量は、0.3重量%以上10重量%以下が好ましい。導電助剤の含有量を0.3重量%以上とすることにより、正極の導電性を向上させ、電子抵抗を低減することができる。一方、導電助剤の含有量を10重量%以下とすることにより、導電助剤によるリチウムイオンの移動の阻害を抑制し、イオン伝導性の低下を抑制することができる。 The content of the conductive assistant in the mixture layer is preferably 0.3% by weight or more and 10% by weight or less. By making the content of the conductive assistant 0.3% by weight or more, the conductivity of the positive electrode can be improved and the electronic resistance can be reduced. On the other hand, by making the content of the conductive assistant 10% by weight or less, the inhibition of the movement of lithium ions by the conductive assistant can be suppressed, and the decrease in ion conductivity can be suppressed.
リチウムイオン二次電池を高エネルギー密度化するためには、正極合剤層中にできるだけ高い割合で正極活物質が含まれていることが好ましく、正極合剤層中の活物質粒子の合計含有量は、80重量%以上が好ましく、85重量%以上がより好ましい。ここで、活物質粒子の合計含有量とは、LMO粒子、LMFP粒子および必要に応じてその他の活物質粒子の含有量の合計を指す。 In order to increase the energy density of a lithium-ion secondary battery, it is preferable that the positive electrode active material is contained in the positive electrode mixture layer at as high a ratio as possible, and the total content of the active material particles in the positive electrode mixture layer is preferably 80% by weight or more, and more preferably 85% by weight or more. Here, the total content of the active material particles refers to the sum of the contents of the LMO particles, the LMFP particles, and other active material particles as necessary.
正極合剤層の厚みは、10μm以上200μm以下が好ましい。合剤層の厚みを10μm以上とすることにより、正極に占める集電体の割合を抑え、エネルギー密度をより向上させることができる。一方、合剤層の厚みを200μm以下とすることにより、充放電反応を合剤層全体に速やかに進行させ、高速充放電特性を向上させることができる。 The thickness of the positive electrode mixture layer is preferably 10 μm or more and 200 μm or less. By making the thickness of the mixture layer 10 μm or more, the proportion of the current collector in the positive electrode can be reduced, and the energy density can be further improved. On the other hand, by making the thickness of the mixture layer 200 μm or less, the charge/discharge reaction can be made to proceed quickly throughout the entire mixture layer, and high-speed charge/discharge characteristics can be improved.
本発明のリチウムイオン二次電池は、上記の正極に加え、負極、セパレータ、電解液を有することが好ましい。電池の形状としては、例えば、角型、巻回型、ラミネート型などが挙げられ、使用する目的に応じて適宜選択することができる。負極を構成する材料としては、例えば、黒鉛、チタン酸リチウム、シリコン酸化物などが挙げられる。セパレータ、電解液についても、任意のものを適宜選択して用いることができる。 The lithium ion secondary battery of the present invention preferably has a negative electrode, a separator, and an electrolyte in addition to the positive electrode. The shape of the battery can be, for example, a square type, a wound type, a laminate type, etc., and can be appropriately selected depending on the purpose of use. Materials constituting the negative electrode can be, for example, graphite, lithium titanate, silicon oxide, etc. The separator and electrolyte can also be selected from any suitable materials.
次に、本発明の正極の製造方法について説明する。 Next, we will explain the method for manufacturing the positive electrode of the present invention.
まず、本発明におけるLMO粒子は、公知の方法に従って固相法あるいは液相法により得ることができるし、市販のマンガン酸リチウム粉末を用いることもできる。本発明におけるLMFP粒子は、固相法、液相法などの任意の手法によって得ることができるが、マンガンと鉄の割合を本発明の範囲内とし、平均粒径が前述の好ましい範囲にある粒子をより簡便に得られる点において、液相法が好適である。液相には、水の他、粒径をナノ粒子まで微細化するために有機溶媒を用いることも好適であり、その溶媒種としては、例えば、エチレングリコール、ジエチレングリコール、トリエチレングリコール、テトラエチレングリコール、2-プロパノール、1,3-プロパンジオール、1,4-ブタンジオールなどのアルコール系溶媒や、ジメチルスルホキシドを用いることが好ましい。合成の過程において、粒子の結晶性を高めるために加圧してもかまわない。また、LMFP粒子に含まれるマンガンと鉄の比率は、原料の仕込み比により所望の範囲に調整することができる。 First, the LMO particles of the present invention can be obtained by a solid-phase method or a liquid-phase method according to a known method, or a commercially available lithium manganate powder can be used. The LMFP particles of the present invention can be obtained by any method such as a solid-phase method or a liquid-phase method, but the liquid-phase method is preferable in that the ratio of manganese to iron is within the range of the present invention and particles having an average particle size in the above-mentioned preferred range can be obtained more easily. In addition to water, it is also preferable to use an organic solvent for the liquid phase in order to refine the particle size to nanoparticles, and the solvent type is preferably, for example, an alcohol solvent such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 2-propanol, 1,3-propanediol, or 1,4-butanediol, or dimethyl sulfoxide. In the synthesis process, pressure may be applied to increase the crystallinity of the particles. In addition, the ratio of manganese to iron contained in the LMFP particles can be adjusted to a desired range by the charging ratio of the raw materials.
液相法によりLMFP粒子を得る場合、平均1次粒径は、例えば、溶媒中の水と有機溶媒の混合比、合成溶液の濃度、合成温度などの条件により、所望の範囲に調整することができる。典型的には、平均粒径を大きくするためには、溶媒中の水の割合を増やすこと、合成溶液の濃度を高めること、合成温度を高めることなどが有効である。 When LMFP particles are obtained by a liquid phase method, the average primary particle size can be adjusted to a desired range by adjusting conditions such as the mixture ratio of water and organic solvent in the solvent, the concentration of the synthesis solution, and the synthesis temperature. Typically, in order to increase the average particle size, it is effective to increase the proportion of water in the solvent, increase the concentration of the synthesis solution, and increase the synthesis temperature.
液相法により得られたLMFP粒子に炭素層を形成するカーボンコート方法としては、LMFP粒子と糖類を混合した後に、不活性ガス雰囲気下において焼成する方法が好ましく用いられる。糖類としては、焼成後の灰分が少ない点から、グルコースやスクロースが好ましい。焼成温度は、500℃以上800℃以下が好ましい。 As a carbon coating method for forming a carbon layer on the LMFP particles obtained by the liquid phase method, a method in which the LMFP particles are mixed with sugars and then baked under an inert gas atmosphere is preferably used. As the sugars, glucose and sucrose are preferred because they have a low ash content after baking. The baking temperature is preferably 500°C or higher and 800°C or lower.
本発明におけるLMFP粒子およびLMO粒子の製造方法としては、得られる2次粒子の粒度分布をできるだけ狭くするために、スプレードライヤーを用いることが好ましい。 In the method of producing LMFP particles and LMO particles in the present invention, it is preferable to use a spray dryer in order to narrow the particle size distribution of the resulting secondary particles as much as possible.
本発明の正極は、例えば、前述のLMFP粒子およびLMO粒子を分散媒に分散させたペーストを、集電体上に塗布し、乾燥し、加圧して合剤層を形成することにより得ることができる。ペーストの製造方法としては、前述のLMFP粒子およびLMO粒子、さらに必要に応じて導電助剤などの添加剤、バインダー、N-メチルピロリジノンなどの分散媒を混合して固練りし、水やN-メチルピロリジノンなどの分散媒を添加して粘度を調整することが好ましい。ペーストの固形分濃度は、塗布方法に応じて適宜選択することができる。塗布膜厚を均一にする観点から、30重量%以上80重量%以下が好ましい。ペーストの各材料は、一度に混合してもよいし、各材料をペースト中に均一に分散させるために、固練りを繰り返しながら、順番をつけて添加して混合してもよい。スラリーの混練装置としては、均一に混練できる点で、プラネタリーミキサーや薄膜旋回型高速ミキサーが好ましい。 The positive electrode of the present invention can be obtained, for example, by applying a paste in which the above-mentioned LMFP particles and LMO particles are dispersed in a dispersion medium onto a current collector, drying, and pressing to form a mixture layer. As a method for producing the paste, it is preferable to mix and knead the above-mentioned LMFP particles and LMO particles, and further, if necessary, additives such as a conductive assistant, a binder, and a dispersion medium such as N-methylpyrrolidinone, and add water or a dispersion medium such as N-methylpyrrolidinone to adjust the viscosity. The solid content concentration of the paste can be appropriately selected depending on the application method. From the viewpoint of making the coating film thickness uniform, it is preferable to be 30% by weight or more and 80% by weight or less. Each material of the paste may be mixed at once, or in order to uniformly disperse each material in the paste, it may be added and mixed in order while repeating kneading. As a kneading device for the slurry, a planetary mixer or a thin film swirl type high-speed mixer is preferable in terms of being able to knead uniformly.
本発明のリチウムイオン二次電池は、例えば、露点が-50℃以下のドライ環境下にて、上記正極を、セパレータを介して負極電極と積層させ、電解液を添加することにより得ることができる。 The lithium-ion secondary battery of the present invention can be obtained, for example, by stacking the above-mentioned positive electrode with a negative electrode via a separator in a dry environment with a dew point of -50°C or less, and adding an electrolyte.
以下、実施例により本発明を具体的に説明するが、本発明はこれらの実施例のみに制限されるものではない。まず、実施例における評価方法について説明する。 The present invention will be specifically explained below using examples, but the present invention is not limited to these examples. First, the evaluation methods used in the examples will be explained.
[測定A]粒子径
各実施例および比較例に用いたLMFP粒子およびLMO粒子を、走査型電子顕微鏡S-5500(株式会社日立ハイテクノロジーズ社製)を用いて、倍率3,000倍にて拡大観察し、無作為に選択した100個の2次粒子についてそれぞれ粒径を測定し、数平均値を算出することにより、粒子径を算出した。ただし、粒子が球形でない場合は、2次元像において測定できる長軸と短軸の平均値をその粒径とした。
[Measurement A] Particle diameter The LMFP particles and LMO particles used in each Example and Comparative Example were observed at a magnification of 3,000 times using a scanning electron microscope S-5500 (manufactured by Hitachi High-Technologies Corporation), and the particle diameter of each of 100 randomly selected secondary particles was measured, and the particle diameter was calculated by calculating the number average value. However, when the particles were not spherical, the average value of the major axis and minor axis that could be measured in the two-dimensional image was used as the particle diameter.
[測定B]正極の出力特性
各実施例および比較例において作製した電極板を直径15.9mmに切り出して正極とし、直径16.1mm、厚さ0.2mmに切り出したリチウム箔を負極とし、セパレータとして“セティーラ”(登録商標)、電解液としてLiPF6を1M含有するエチレンカーボネート:ジエチルカーボネート=3:7(体積比)を用いて、2032型コイン電池を作製した。
[Measurement B] Output characteristics of positive electrode A 2032-type coin battery was produced by cutting the electrode plate produced in each Example and Comparative Example to a diameter of 15.9 mm to form a positive electrode, using a lithium foil cut to a diameter of 16.1 mm and a thickness of 0.2 mm to form a negative electrode, using "Setira" (registered trademark) as a separator, and using ethylene carbonate:diethyl carbonate = 3:7 (volume ratio) containing 1 M LiPF6 as an electrolyte.
作製した2032型コイン電池について、カットオフ電圧を2.5V、最大充電電圧を4.3Vとし、充放電を0.1Cレートとして2回、続けて充放電を5Cレートとして2回行った。それぞれの充放電レートについて、2回目の放電からエネルギー密度(Wh/kg)を測定し、5Cレートと0.1Cレートにおけるエネルギー密度の比を計算し、出力特性とした。エネルギー密度の比が1に近いほど、出力特性に優れる。 The 2032-type coin battery thus fabricated was charged and discharged twice at a 0.1C rate, followed by two cycles at a 5C rate, with a cutoff voltage of 2.5V and a maximum charging voltage of 4.3V. For each charge and discharge rate, the energy density (Wh/kg) was measured from the second discharge, and the ratio of the energy density at the 5C rate and the 0.1C rate was calculated to determine the output characteristics. The closer the energy density ratio is to 1, the better the output characteristics are.
[測定C]正極の過充電耐性
各実施例および比較例において作製した電極板と、負極電極として市販のカーボン系負極(負極活物質:日立化成株式会社製 人造黒鉛MAG)、セパレータとして“セティーラ”(登録商標)、電解液としてLiPF6を1M含有するエチレンカーボネート:ジエチルカーボネート=3:7(体積比)を用いて、1Ahセルの積層ラミネートセルを作製した。積層数は正極(サイズ:70mm×40mm)を7層、負極(サイズ:74mm×44mm)を8層とし、対向する正極と負極の容量比率(NP比)は1.05とした。
[Measurement C] Overcharge resistance of positive electrode A 1 Ah cell was prepared using the electrode plate prepared in each Example and Comparative Example, a commercially available carbon-based negative electrode (negative electrode active material: artificial graphite MAG manufactured by Hitachi Chemical Co., Ltd.) as a negative electrode, "Setira" (registered trademark) as a separator, and ethylene carbonate:diethyl carbonate = 3:7 (volume ratio) containing 1M LiPF 6 as an electrolyte. The number of layers was 7 layers for the positive electrode (size: 70 mm x 40 mm) and 8 layers for the negative electrode (size: 74 mm x 44 mm), and the capacity ratio (NP ratio) of the opposing positive and negative electrodes was 1.05.
作製したラミネートセルを、25℃環境の下、1Cレートで、定格容量の250%(2.5Ah)に到達するか、充電電圧が10Vに到達するまで充電し続け(過充電)、セルの最大温度を測定した。最大温度が低いほど、過充電耐性に優れる。 The laminated cell thus produced was charged (overcharged) at a rate of 1C in a 25°C environment until it reached 250% (2.5 Ah) of the rated capacity or the charging voltage reached 10 V, and the maximum temperature of the cell was measured. The lower the maximum temperature, the better the overcharge resistance.
[測定D]正極のサイクル耐性
測定Cと同様に作製したラミネート型セルを、25℃環境下、0.1Cレートで3回充放電させた後、55℃の環境下、1Cレートでの充放電を繰り返すサイクル試験を実施した。55℃の環境下における1回目の放電試験でのエネルギー密度を100%とし、エネルギー密度が80%を下回るまでのサイクル回数を測定し、サイクル耐性として評価した。サイクル回数が大きいほど、サイクル耐性に優れる。
[Measurement D] Cycle resistance of positive electrode A laminated cell prepared in the same manner as in measurement C was charged and discharged three times at a 0.1C rate in a 25°C environment, and then a cycle test was performed in which charging and discharging were repeated at a 1C rate in a 55°C environment. The energy density in the first discharge test in a 55°C environment was taken as 100%, and the number of cycles until the energy density fell below 80% was measured and evaluated as cycle resistance. The greater the number of cycles, the better the cycle resistance.
[実施例1]
(工程1:LMO粒子の作製)
純水150gに硝酸リチウム50ミリモルと硝酸マンガン(II)六水和物100ミリモルを溶解し、LMO前駆体溶液を調製した。このLMO前駆体溶液を超音波噴霧化装置(オムロン社製超音波ネブライザーNE-U12)に導入して噴霧化した後、800℃に加熱した電気炉内に導入して乾燥および熱分解を施し、2次粒子であるLMO粒子を得た。
[Example 1]
(Step 1: Preparation of LMO particles)
An LMO precursor solution was prepared by dissolving 50 mmol of lithium nitrate and 100 mmol of manganese (II) nitrate hexahydrate in 150 g of pure water. This LMO precursor solution was introduced into an ultrasonic atomizer (Omron Corporation, ultrasonic nebulizer NE-U12) and atomized, and then introduced into an electric furnace heated to 800° C. for drying and pyrolysis to obtain LMO particles, which are secondary particles.
(工程2:LMFP粒子の作製)
純水150gにジメチルスルホキシド200gを加え、水酸化リチウム1水和物を360ミリモル添加した。得られた溶液に、85重量%リン酸水溶液を用いてリン酸を120ミリモルさらに添加し、さらに硫酸マンガン(II)1水和物を96ミリモル、硫酸鉄(II)7水和物を24ミリモル添加した。得られた溶液をオートクレーブに移し、容器内が150℃を維持するように4時間加熱保持した。加熱後に溶液の上澄みを捨て、沈殿物としてリン酸マンガン鉄リチウムLiMn0.8Fe0.2PO4を得た。得られたリン酸マンガン鉄リチウムを純水にて洗浄した後に、遠心分離により上澄みを除去する操作を5回繰り返し、最後に再度純水を加えて分散液とした。続いて分散液中のリン酸マンガン鉄リチウムの15重量%と同重量のグルコースを分散液に添加して溶解させた後、純水を加えて分散液の固形分濃度を20重量%に調整し、LMFP分散液を得た。
(Step 2: Preparation of LMFP particles)
200 g of dimethyl sulfoxide was added to 150 g of pure water, and 360 mmol of lithium hydroxide monohydrate was added. 120 mmol of phosphoric acid was further added to the obtained solution using an 85 wt% aqueous phosphoric acid solution, and 96 mmol of manganese (II) sulfate monohydrate and 24 mmol of iron (II) sulfate heptahydrate were further added. The obtained solution was transferred to an autoclave and heated and held for 4 hours so that the temperature inside the container was maintained at 150 ° C. After heating, the supernatant of the solution was discarded, and lithium manganese iron phosphate LiMn 0.8 Fe 0.2 PO 4 was obtained as a precipitate. After washing the obtained lithium manganese iron phosphate with pure water, the operation of removing the supernatant by centrifugation was repeated five times, and finally pure water was added again to obtain a dispersion. Subsequently, glucose was added to the dispersion in an amount equal to 15% by weight of the lithium manganese iron phosphate in the dispersion and dissolved, and then pure water was added to adjust the solid concentration of the dispersion to 20% by weight, to obtain an LMFP dispersion.
得られたLMFP分散液をスプレードライヤー(藤崎電機株式会社製 MDL-050B)を用いて200℃の熱風により乾燥し、2次粒子を得た。得られた2次粒子を、ロータリーキルン(高砂工業株式会社製 デスクトップロータリーキルン)を用いて窒素雰囲気下700℃で4時間加熱し、カーボンコートされたLMFP粒子を得た。 The resulting LMFP dispersion was dried with hot air at 200°C using a spray dryer (MDL-050B, manufactured by Fujisaki Electric Co., Ltd.) to obtain secondary particles. The resulting secondary particles were heated at 700°C for 4 hours in a nitrogen atmosphere using a rotary kiln (Desktop Rotary Kiln, manufactured by Takasago Industrial Co., Ltd.) to obtain carbon-coated LMFP particles.
(工程3:電極板の作製)
アセチレンブラック(デンカ株式会社製 Li-400)とバインダー(株式会社クレハKFポリマー L#9305)を混合した後、上記方法により得られたLMO粒子とLMFP粒子を重量比2:1の割合で添加して乳鉢で固練りを実施した。その際、含まれる各材料の重量比は造粒体(LMO粒子とカーボンコートされたLMFP粒子の合計):アセチレンブラック:バインダーが90:5:5となるようにした。その後、N-メチルピロリジノンを添加して固形分が48重量%となるように調整し、スラリー状の電極ペーストを得た。得られたペーストに流動性がでるまでN-メチルピロリジノンを追加し、薄膜旋回型高速ミキサー(プライミクス株式会社製“フィルミックス”(登録商標)40-L型)を用いて、40m/秒の撹拌条件で30秒間処理した。
(Step 3: Preparation of electrode plate)
After mixing acetylene black (Li-400 manufactured by Denka Co., Ltd.) and binder (L#9305 manufactured by Kureha KF Polymer Co., Ltd.), the LMO particles and LMFP particles obtained by the above method were added in a weight ratio of 2:1, and kneaded in a mortar. At that time, the weight ratio of each material contained was granules (total of LMO particles and carbon-coated LMFP particles): acetylene black: binder was 90:5:5. Thereafter, N-methylpyrrolidinone was added to adjust the solid content to 48% by weight, and a slurry-like electrode paste was obtained. N-methylpyrrolidinone was added until the obtained paste had fluidity, and the paste was treated for 30 seconds under stirring conditions of 40 m/s using a thin film swirling high-speed mixer ("Filmix" (registered trademark) 40-L type manufactured by Primix Corporation).
得られた電極ペーストを、ドクターブレード(300μm)を用いてアルミニウム箔(厚さ18μm)に塗布し、80℃30分間乾燥した後、プレスを施し電極板を作製した。 The obtained electrode paste was applied to aluminum foil (thickness 18 μm) using a doctor blade (300 μm), dried at 80°C for 30 minutes, and then pressed to produce an electrode plate.
[実施例2]
工程3におけるLMO粒子とLMFP粒子の重量比を3:1としたこと以外は実施例1と同様にして、電極板を作製した。
[Example 2]
An electrode plate was produced in the same manner as in Example 1, except that in step 3, the weight ratio of the LMO particles to the LMFP particles was 3:1.
[実施例3]
工程2におけるLMFP分散液の固形分濃度を40重量%としたこと以外は実施例1と同様にして、電極板を作製した。
[Example 3]
An electrode plate was produced in the same manner as in Example 1, except that the solid content concentration of the LMFP dispersion in step 2 was 40% by weight.
[実施例4]
工程2における硫酸マンガン(II)1水和物の添加量を84ミリモル、硫酸鉄(II)7水和物の添加量を36ミリモルとし、加熱温度を250℃としたこと以外は実施例3と同様にして、電極板を作製した。
[Example 4]
An electrode plate was prepared in the same manner as in Example 3, except that in step 2, the amount of manganese (II) sulfate monohydrate added was 84 mmol, the amount of iron (II) sulfate heptahydrate added was 36 mmol, and the heating temperature was 250° C.
[実施例5]
工程2において最初に添加する純水の添加量を100g、ジメチルスルホキシドの添加量を120gとしたこと以外は実施例3と同様にして、電極板を作製した。
[Example 5]
An electrode plate was prepared in the same manner as in Example 3, except that the amount of pure water added initially in step 2 was 100 g and the amount of dimethyl sulfoxide added was 120 g.
[実施例6]
工程2における硫酸マンガン(II)1水和物の添加量を108ミリモル、硫酸鉄(II)7水和物の添加量を12ミリモルとしたこと以外は実施例3と同様にして、電極板を作製した。
[Example 6]
An electrode plate was prepared in the same manner as in Example 3, except that the amount of manganese (II) sulfate monohydrate added in step 2 was 108 mmol, and the amount of iron (II) sulfate heptahydrate added was 12 mmol.
[実施例7]
工程2におけるグルコースの添加量をリン酸マンガン鉄リチウムの7重量%と同重量にしたこと以外は実施例3と同様にして、電極板を作製した。
[Example 7]
An electrode plate was prepared in the same manner as in Example 3, except that the amount of glucose added in step 2 was set to be equal to 7% by weight of the lithium iron manganese phosphate.
[実施例8]
工程2におけるグルコースの添加量をリン酸マンガン鉄リチウムの25重量%と同重量にしたこと以外は実施例3と同様にして、電極板を作製した。
[Example 8]
An electrode plate was prepared in the same manner as in Example 3, except that the amount of glucose added in step 2 was set to be equal to 25% by weight of the lithium iron manganese phosphate.
[実施例9]
工程2における硫酸マンガン(II)1水和物の添加量60ミリモル、硫酸鉄(II)7水和物の添加量を60ミリモルとしたこと以外は実施例8と同様にして、電極板を作製した。
[Example 9]
An electrode plate was prepared in the same manner as in Example 8, except that the amount of manganese (II) sulfate monohydrate added in step 2 was 60 mmol, and the amount of iron (II) sulfate heptahydrate added was 60 mmol.
[実施例10]
工程3において、LMO粒子とLMFP粒子に加え層状酸化物系活物質粒子(ユミコア社製LiNi0.5Co0.2Mn0.3O2 平均粒径13μmの造粒体)を、LMO粒子:LMFP粒子:層状酸化物系活物質粒子割合が60:30:10(重量比)となるように添加し、含まれる各材料の重量比が造粒体(LMO粒子とカーボンコートされたLMFP粒子と層状酸化物系活物質粒子の合計):アセチレンブラック:バインダーが90:5:5となるようにしたこと以外は実施例1と同様にして、電極板を作製した。
[Example 10]
In step 3, in addition to the LMO particles and LMFP particles , layered oxide active material particles (granules of LiNi0.5Co0.2Mn0.3O2 with an average particle size of 13 μm manufactured by Umicore ) were added so that the ratio of LMO particles:LMFP particles:layered oxide active material particles was 60:30:10 (weight ratio), and the weight ratio of each material contained was granules (total of LMO particles, carbon-coated LMFP particles, and layered oxide active material particles):acetylene black:binder was 90:5:5. An electrode plate was produced in the same manner as in Example 1.
[実施例11]
工程1における硝酸マンガン(II)六水和物の添加量を95ミリモルとし、さらにLMO前駆体溶液に硝酸亜鉛六水和物5ミリモルを添加したこと以外は実施例1と同様にして、電極板を作製した。
[Example 11]
An electrode plate was prepared in the same manner as in Example 1, except that the amount of manganese (II) nitrate hexahydrate added in step 1 was 95 mmol, and further, 5 mmol of zinc nitrate hexahydrate was added to the LMO precursor solution.
[比較例1]
工程2におけるLMFP分散液中の固形分濃度を60重量%としたこと以外は実施例1と同様にして、電極板を作製した。
[Comparative Example 1]
An electrode plate was produced in the same manner as in Example 1, except that the solid content concentration in the LMFP dispersion in step 2 was 60% by weight.
[比較例2]
工程2におけるLMFP分散液中の固形分濃度を8重量%としたこと以外は実施例1と同様にして、電極板を作製した。
[Comparative Example 2]
An electrode plate was produced in the same manner as in Example 1, except that the solid content concentration in the LMFP dispersion in step 2 was 8% by weight.
[比較例3]
工程3におけるLMO粒子とLMFP粒子の重量比を5:1としたこと以外は実施例3と同様にして、電極板を作製した。
[Comparative Example 3]
An electrode plate was produced in the same manner as in Example 3, except that in step 3, the weight ratio of the LMO particles to the LMFP particles was 5:1.
[比較例4]
工程3におけるLMO粒子とLMFP粒子の重量比を0.5:1としたこと以外は実施例3と同様にして、電極板を作製した。
[Comparative Example 4]
An electrode plate was produced in the same manner as in Example 3, except that in step 3, the weight ratio of the LMO particles to the LMFP particles was 0.5:1.
各実施例および比較例の評価結果を表1に示す。 The evaluation results for each example and comparative example are shown in Table 1.
Claims (5)
リン酸マンガン鉄リチウム粒子の粒子径に対するスピネル系リチウム金属酸化物粒子の粒子径の比(スピネル系リチウム金属酸化物粒子の粒子径/リン酸マンガン鉄リチウム粒子の粒子径)が2.0以上10.0以下であり、
リン酸マンガン鉄リチウム粒子の含有量に対するスピネル系リチウム金属酸化物粒子の含有量の重量比(スピネル系リチウム金属酸化物粒子の含有量/リン酸マンガン鉄リチウム粒子の含有量)が1.0以上4.0以下である、リチウムイオン二次電池用正極。 A positive electrode for a lithium ion secondary battery containing spinel-based lithium metal oxide particles and lithium manganese iron phosphate particles,
a ratio of a particle size of the spinel-based lithium metal oxide particles to a particle size of the lithium manganese iron phosphate particles (particle size of the spinel-based lithium metal oxide particles/particle size of the lithium manganese iron phosphate particles) is 2.0 or more and 10.0 or less;
A positive electrode for a lithium ion secondary battery, in which a weight ratio of a content of spinel-based lithium metal oxide particles to a content of lithium manganese iron phosphate particles (content of spinel-based lithium metal oxide particles/content of lithium manganese iron phosphate particles) is 1.0 or more and 4.0 or less.
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JP2015053252A (en) | 2013-08-08 | 2015-03-19 | トヨタ自動車株式会社 | Positive electrode active material for lithium ion secondary battery |
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JP2007103298A (en) | 2005-10-07 | 2007-04-19 | Toyota Central Res & Dev Lab Inc | Positive electrode active material, its manufacturing method, and aqueous lithium secondary battery |
JP2011113783A (en) | 2009-11-26 | 2011-06-09 | Sony Corp | Positive electrode active material for nonaqueous electrolyte battery, nonaqueous electrolyte battery, high-output electronic equipment, and automobile |
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