JP2020187988A - Manufacturing method of negative electrode material for lithium ion secondary battery, negative electrode material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents
Manufacturing method of negative electrode material for lithium ion secondary battery, negative electrode material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery Download PDFInfo
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- JP2020187988A JP2020187988A JP2019093935A JP2019093935A JP2020187988A JP 2020187988 A JP2020187988 A JP 2020187988A JP 2019093935 A JP2019093935 A JP 2019093935A JP 2019093935 A JP2019093935 A JP 2019093935A JP 2020187988 A JP2020187988 A JP 2020187988A
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- negative electrode
- secondary battery
- ion secondary
- electrode material
- lithium ion
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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
Abstract
Description
本開示は、リチウムイオン二次電池用負極材の製造方法、リチウムイオン二次電池用負極材、リチウムイオン二次電池用負極、及びリチウムイオン二次電池に関する。 The present disclosure relates to a method for manufacturing a negative electrode material for a lithium ion secondary battery, a negative electrode material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery.
リチウムイオン二次電池は、他の二次電池であるニッケルカドミウム電池、ニッケル水素電池、及び鉛蓄電池に比べて軽量で高い充放電容量を有することから、近年、電気自動車、ハイブリッド型電気自動車用等の電源として期待されている。電気自動車、ハイブリッド型電気自動車等が普及するためには、リチウムイオン二次電池のさらなる高容量化が望まれる。 Lithium-ion secondary batteries are lighter in weight and have higher charge / discharge capacity than other secondary batteries such as nickel cadmium batteries, nickel hydrogen batteries, and lead storage batteries. Therefore, in recent years, they are used for electric vehicles, hybrid electric vehicles, etc. It is expected as a power source for. In order for electric vehicles, hybrid electric vehicles, and the like to become widespread, it is desired to further increase the capacity of lithium ion secondary batteries.
リチウムイオン二次電池を高電気容量化するために、その負極活物質としてシリコンを利用することが注目されている。一般にリチウムイオン二次電池に用いられる負極活物質として黒鉛があり、黒鉛の理論電気容量は３７２ｍＡｈ／ｇである。シリコンの理論電気容量は、黒鉛の約１１倍の４２００ｍＡｈ／ｇであり、シリコンはリチウムイオン二次電池の高電気容量化に有効な材料といえる。 In order to increase the electric capacity of lithium ion secondary batteries, attention is being paid to the use of silicon as the negative electrode active material. Graphite is generally used as a negative electrode active material in a lithium ion secondary battery, and the theoretical electric capacity of graphite is 372 mAh / g. The theoretical electric capacity of silicon is 4200 mAh / g, which is about 11 times that of graphite, and it can be said that silicon is an effective material for increasing the electric capacity of a lithium ion secondary battery.
しかしながら、シリコンは充電時に体積膨張する性質があり、満充電時の理論体積膨張率は４００％である。シリコンの体積膨張はリチウムイオン二次電池の電極の劣化を招くだけでなく、電池自体の形状安定性を損なうおそれがある。また、充放電による体積の膨張収縮を繰り返すことによって、シリコン自体が崩壊又は微粉化し、充放電効率及び寿命を低下させるという課題がある。 However, silicon has a property of volume expansion during charging, and the theoretical volume expansion coefficient when fully charged is 400%. The volume expansion of silicon not only causes deterioration of the electrodes of the lithium ion secondary battery, but also may impair the shape stability of the battery itself. Further, there is a problem that the silicon itself collapses or becomes finely divided by repeating expansion and contraction of the volume due to charging / discharging, and the charging / discharging efficiency and the life are lowered.
シリコンの体積膨張による応力を緩和する方法として、これまでシリコンとリチウムシリケートとの複合化が検討されてきた。シリコンとリチウムシリケートを複合化する方法としては、例えば特許文献１及び特許文献２に記載の方法が知られている。特許文献１では、シリコン及びリチウムシリケートの混合物を粉砕してホットプレス機で圧縮した後、粉砕して、リチウムシリケート相中にシリコン粒子が分散した負極活物質を作製している。特許文献２では、シリコン粉末とリチウムシリケート粉末を用いたメカニカルアロイによって、シリコンの一次粒子がリチウムシリケートで被覆された負極活物質を作製している。 As a method of relieving stress due to volume expansion of silicon, the combination of silicon and lithium silicate has been studied so far. As a method for synthesizing silicon and lithium silicate, for example, the methods described in Patent Document 1 and Patent Document 2 are known. In Patent Document 1, a mixture of silicon and lithium silicate is pulverized, compressed by a hot press machine, and then pulverized to produce a negative electrode active material in which silicon particles are dispersed in the lithium silicate phase. In Patent Document 2, a negative electrode active material in which primary particles of silicon are coated with lithium silicate is produced by a mechanical alloy using silicon powder and lithium silicate powder.
しかしながら、シリコンとリチウムシリケートの複合粒子を用いた負極材であっても、サイクル特性には依然として改良の余地があった。 However, even in the negative electrode material using the composite particles of silicon and lithium silicate, there is still room for improvement in the cycle characteristics.
上記事情に鑑み、本開示は、サイクル特性に優れる負極を製造可能なリチウムイオン二次電池用負極材の製造方法及びリチウムイオン二次電池用負極材、サイクル特性に優れるリチウムイオン二次電池用負極、並びにこれを備えるリチウムイオン二次電池を提供することを課題とする。 In view of the above circumstances, the present disclosure describes a method for producing a negative electrode material for a lithium ion secondary battery capable of producing a negative electrode having excellent cycle characteristics, a negative electrode material for a lithium ion secondary battery, and a negative electrode for a lithium ion secondary battery having excellent cycle characteristics. , And to provide a lithium ion secondary battery equipped with the same.
上記課題を解決するための手段には、以下の実施態様が含まれる。
＜１＞ シリコン粒子とリチウムシリケート粒子との混合物を、前記リチウムシリケート粒子の溶融温度を超える温度で加熱することを含む、リチウムイオン二次電池用負極材の製造方法。
＜２＞ 前記加熱の温度が１１００℃〜１４００℃である、＜１＞に記載のリチウムイオン二次電池用負極材の製造方法。
＜３＞ 前記シリコン粒子の平均粒子径が１００ｎｍ以下である、＜１＞又は＜２＞に記載のリチウムイオン二次電池用負極材の製造方法。
＜４＞ 前記シリコン粒子と前記リチウムシリケート粒子との合計量に対する前記シリコン粒子の含有率が３０質量％〜９０質量％である、＜１＞〜＜３＞のいずれか１項に記載のリチウムイオン二次電池用負極材の製造方法。
＜５＞ 前記リチウムシリケート粒子がＬｉ２Ｓｉ２Ｏ５を含む、＜１＞〜＜４＞のいずれか１項に記載のリチウムイオン二次電池用負極材の製造方法。
＜６＞ 前記負極材の内部の空隙率が１．０％未満である、＜１＞〜＜５＞のいずれか１項に記載のリチウムイオン二次電池用負極材の製造方法。
＜７＞ 前記負極材中のリチウムシリケート粒子が結晶構造を有する、＜１＞〜＜６＞のいずれか１項に記載のリチウムイオン二次電池用負極材の製造方法。
＜８＞ 前記加熱の前に、前記混合物をプレス成形によって成形することをさらに含む、＜１＞〜＜７＞のいずれか１項に記載のリチウムイオン二次電池用負極材の製造方法。
＜９＞ ＜１＞〜＜８＞のいずれか１項に記載の製造方法によって製造される負極材を含むリチウムイオン二次電池用負極。
＜１０＞ ＜９＞に記載の負極を備えるリチウムイオン二次電池。
＜１１＞ シリコン粒子と前記シリコン粒子を被覆しているリチウムシリケートとを含む負極材であって、前記負極材の内部の空隙率が１．０％未満である、リチウムイオン二次電池用負極材。
＜１２＞ 前記リチウムシリケートが結晶構造を有する、＜１１＞に記載のリチウムイオン二次電池用負極材。
＜１３＞ 前記シリコン粒子の粒子径が１００ｎｍ以下である、＜１１＞又は＜１２＞に記載のリチウムイオン二次電池用負極材。
＜１４＞ 前記シリコン粒子と前記リチウムシリケートの合計量に対する前記シリコン粒子の含有率が３０質量％〜９０質量％である、＜１１＞〜＜１３＞のいずれか１項に記載のリチウムイオン二次電池用負極材。
＜１５＞ 前記リチウムシリケートがＬｉ２Ｓｉ２Ｏ５を含む、＜１１＞〜＜１４＞のいずれか１項に記載のリチウムイオン二次電池用負極材。
＜１６＞ ＜１１＞〜＜１５＞のいずれか１項に記載の負極材を備えるリチウムイオン二次電池用負極。
＜１７＞ ＜１６＞に記載の負極を備えるリチウムイオン二次電池。
Means for solving the above problems include the following embodiments.
<1> A method for producing a negative electrode material for a lithium ion secondary battery, which comprises heating a mixture of silicon particles and lithium silicate particles at a temperature exceeding the melting temperature of the lithium silicate particles.
<2> The method for producing a negative electrode material for a lithium ion secondary battery according to <1>, wherein the heating temperature is 1100 ° C to 1400 ° C.
<3> The method for producing a negative electrode material for a lithium ion secondary battery according to <1> or <2>, wherein the average particle size of the silicon particles is 100 nm or less.
<4> The lithium ion according to any one of <1> to <3>, wherein the content of the silicon particles with respect to the total amount of the silicon particles and the lithium silicate particles is 30% by mass to 90% by mass. A method for manufacturing a negative electrode material for a secondary battery.
<5> The method for producing a negative electrode material for a lithium ion secondary battery according to any one of <1> to <4>, wherein the lithium silicate particles contain Li 2 Si 2 O 5 .
<6> The method for producing a negative electrode material for a lithium ion secondary battery according to any one of <1> to <5>, wherein the porosity inside the negative electrode material is less than 1.0%.
<7> The method for producing a negative electrode material for a lithium ion secondary battery according to any one of <1> to <6>, wherein the lithium silicate particles in the negative electrode material have a crystal structure.
<8> The method for producing a negative electrode material for a lithium ion secondary battery according to any one of <1> to <7>, further comprising molding the mixture by press molding before the heating.
<9> A negative electrode for a lithium ion secondary battery containing a negative electrode material manufactured by the manufacturing method according to any one of <1> to <8>.
<10> A lithium ion secondary battery comprising the negative electrode according to <9>.
<11> A negative electrode material containing silicon particles and a lithium silicate covering the silicon particles, wherein the void ratio inside the negative electrode material is less than 1.0%, and the negative electrode material for a lithium ion secondary battery. ..
<12> The negative electrode material for a lithium ion secondary battery according to <11>, wherein the lithium silicate has a crystal structure.
<13> The negative electrode material for a lithium ion secondary battery according to <11> or <12>, wherein the silicon particles have a particle size of 100 nm or less.
<14> The lithium ion secondary according to any one of <11> to <13>, wherein the content of the silicon particles with respect to the total amount of the silicon particles and the lithium silicate is 30% by mass to 90% by mass. Negative electrode material for batteries.
<15> The negative electrode material for a lithium ion secondary battery according to any one of <11> to <14>, wherein the lithium silicate contains Li 2 Si 2 O 5 .
<16> A negative electrode for a lithium ion secondary battery comprising the negative electrode material according to any one of <11> to <15>.
<17> A lithium ion secondary battery comprising the negative electrode according to <16>.
本開示によれば、サイクル特性に優れる負極を製造可能なリチウムイオン二次電池用負極材の製造方法及びリチウムイオン二次電池用負極材、サイクル特性に優れるリチウムイオン二次電池用負極、並びにこれを備えるリチウムイオン二次電池が提供される。 According to the present disclosure, a method for manufacturing a negative electrode material for a lithium ion secondary battery capable of producing a negative electrode having excellent cycle characteristics, a negative electrode material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery having excellent cycle characteristics, and the like. A lithium ion secondary battery is provided.
以下、本発明を実施するための形態について詳細に説明する。但し、本発明は以下の実施形態に限定されるものではない。以下の実施形態において、その構成要素（要素ステップ等も含む）は、特に明示した場合を除き、必須ではない。数値及びその範囲についても同様であり、本発明を制限するものではない。 Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including element steps and the like) are not essential unless otherwise specified. The same applies to the numerical values and their ranges, and does not limit the present invention.
本開示において「工程」との語には、他の工程から独立した工程に加え、他の工程と明確に区別できない場合であってもその工程の目的が達成されれば、当該工程も含まれる。
本開示において「〜」を用いて示された数値範囲には、「〜」の前後に記載される数値がそれぞれ最小値及び最大値として含まれる。
本開示中に段階的に記載されている数値範囲において、一つの数値範囲で記載された上限値又は下限値は、他の段階的な記載の数値範囲の上限値又は下限値に置き換えてもよい。また、本開示中に記載されている数値範囲において、その数値範囲の上限値又は下限値は、実施例に示されている値に置き換えてもよい。
本開示において各成分は該当する物質を複数種含んでいてもよい。組成物中に各成分に該当する物質が複数種存在する場合、各成分の含有率又は含有量は、特に断らない限り、組成物中に存在する当該複数種の物質の合計の含有率又は含有量を意味する。
本開示において各成分に該当する粒子は複数種含まれていてもよい。組成物中に各成分に該当する粒子が複数種存在する場合、各成分の粒子径は、特に断らない限り、組成物中に存在する当該複数種の粒子の混合物についての値を意味する。
本開示において「層」との語には、当該層が存在する領域を観察したときに、当該領域の全体に形成されている場合に加え、当該領域の一部にのみ形成されている場合も含まれる。
本開示において「積層」との語は、層を積み重ねることを示し、二以上の層が結合されていてもよく、二以上の層が着脱可能であってもよい。
本開示において「（メタ）アクリレート」とは、アクリレート及びメタクリレートの少なくとも一方を意味し、「（メタ）アクリロニトリル」とはアクリロニトリル及びメタクリロニトリルの少なくとも一方を意味する。
In the present disclosure, the term "process" includes not only a process independent of other processes but also the process if the purpose of the process is achieved even if it cannot be clearly distinguished from the other process. ..
The numerical range indicated by using "~" in the present disclosure includes the numerical values before and after "~" as the minimum value and the maximum value, respectively.
In the numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described stepwise. .. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.
In the present disclosure, each component may contain a plurality of applicable substances. When a plurality of substances corresponding to each component are present in the composition, the content rate or content of each component is the total content rate or content of the plurality of substances present in the composition unless otherwise specified. Means quantity.
In the present disclosure, a plurality of types of particles corresponding to each component may be contained. When a plurality of particles corresponding to each component are present in the composition, the particle size of each component means a value for a mixture of the plurality of particles present in the composition unless otherwise specified.
In the present disclosure, the term "layer" refers to the case where the layer is formed in the entire region when the region where the layer is present is observed, and also when the layer is formed only in a part of the region. included.
In the present disclosure, the term "laminated" refers to stacking layers, and two or more layers may be bonded or the two or more layers may be removable.
In the present disclosure, "(meth) acrylate" means at least one of acrylate and methacrylate, and "(meth) acrylonitrile" means at least one of acrylonitrile and methacrylonitrile.
≪リチウムイオン二次電池用負極材の製造方法≫
本開示のリチウムイオン二次電池用負極材の製造方法は、シリコン粒子とリチウムシリケート粒子との混合物を、前記リチウムシリケート粒子の溶融温度を超える温度で加熱することを含む。ここで、シリコン粒子とリチウムシリケート粒子との混合物とは、シリコン粒子とリチウムシリケート粒子とが別個に存在している混合物を表し、シリコンとリチウムシリケートの複合粒子を表すものではない。
≪Manufacturing method of negative electrode material for lithium ion secondary battery≫
The method for producing a negative electrode material for a lithium ion secondary battery of the present disclosure includes heating a mixture of silicon particles and lithium silicate particles at a temperature exceeding the melting temperature of the lithium silicate particles. Here, the mixture of silicon particles and lithium silicate particles represents a mixture in which silicon particles and lithium silicate particles are present separately, and does not represent composite particles of silicon and lithium silicate.
本開示の製造方法によれば、サイクル特性に優れる負極を製造可能である。この理由は必ずしも明らかではないが、以下のように考えることができる。本開示の製造方法はリチウムシリケート粒子を溶融させる工程を含むため、製造された負極材の粒子内部には空隙が少なくなり、シリコン粒子が高密度のリチウムシリケートに内包された状態となる。その結果、シリコン粒子の膨張による負極材の崩壊を抑制することができ、負極のサイクル特性を好適に向上させることができると考えられる。 According to the manufacturing method of the present disclosure, it is possible to manufacture a negative electrode having excellent cycle characteristics. The reason for this is not always clear, but it can be thought of as follows. Since the manufacturing method of the present disclosure includes a step of melting the lithium silicate particles, the number of voids inside the particles of the manufactured negative electrode material is reduced, and the silicon particles are contained in the high-density lithium silicate. As a result, it is considered that the collapse of the negative electrode material due to the expansion of the silicon particles can be suppressed, and the cycle characteristics of the negative electrode can be suitably improved.
原料として用いられるシリコン粒子は、結晶性であってもよく、非晶性であってもよく、これらが混合されたものであってもよい。 The silicon particles used as a raw material may be crystalline, amorphous, or a mixture of these.
混合物中のシリコン粒子の平均粒子径は特に制限されない。シリコン粒子の平均粒子径は、５００ｎｍ以下であってもよい。充放電特性の観点からは、シリコン粒子の平均粒子径は３００ｎｍ以下であることが好ましく、１００ｎｍ以下であることがより好ましく、５０ｎｍ以下であることがさらに好ましい。シリコン粒子の平均粒子径の下限値は特に制限されず、２０ｎｍ以上であってもよい。シリコン粒子の平均粒子径は、後述の負極材の平均粒子径と同様の方法で測定することができる。 The average particle size of the silicon particles in the mixture is not particularly limited. The average particle size of the silicon particles may be 500 nm or less. From the viewpoint of charge / discharge characteristics, the average particle size of the silicon particles is preferably 300 nm or less, more preferably 100 nm or less, and further preferably 50 nm or less. The lower limit of the average particle diameter of the silicon particles is not particularly limited and may be 20 nm or more. The average particle size of the silicon particles can be measured by the same method as the average particle size of the negative electrode material described later.
原料として用いられるリチウムシリケート粒子におけるリチウムシリケートの組成は特に限定されない。リチウムシリケートとしては、例えば、Ｌｉ４ＳｉＯ４、Ｌｉ２Ｓｉ２Ｏ５、Ｌｉ６Ｓｉ２Ｏ７、又はＬｉ２ＳｉＯ３が挙げられる。リチウムシリケートは１種を単独で用いても２種以上を併用してもよい。なかでも、Ｌｉ２Ｓｉ２Ｏ５を用いると、得られる負極の充放電特性が良好となる傾向にある。 The composition of lithium silicate in the lithium silicate particles used as a raw material is not particularly limited. Examples of the lithium silicate include Li 4 SiO 4 , Li 2 Si 2 O 5 , Li 6 Si 2 O 7 , and Li 2 SiO 3 . One type of lithium silicate may be used alone, or two or more types may be used in combination. In particular, when Li 2 Si 2 O 5 is used, the charge / discharge characteristics of the obtained negative electrode tend to be good.
原料として用いられるリチウムシリケート粒子は結晶性であってもよく、非晶性であってもよく、これらが混合されたものであってもよい。 The lithium silicate particles used as a raw material may be crystalline, amorphous, or a mixture of these.
リチウムシリケート粒子の平均粒子径は特に制限されず、例えば、１０μｍ〜１００μｍであってもよい。リチウムシリケート粒子の平均粒子径は、後述の負極材の平均粒子径と同様の方法で測定することができる。 The average particle size of the lithium silicate particles is not particularly limited, and may be, for example, 10 μm to 100 μm. The average particle size of the lithium silicate particles can be measured by the same method as the average particle size of the negative electrode material described later.
本開示の製造方法では、まず、シリコン粒子とリチウムシリケート粒子との混合物を準備する。シリコン粒子とリチウムシリケート粒子との混合物を得る方法は特に制限されない。例えば、予め所望の粒子径に粉砕されたシリコン粒子及びリチウムシリケート粒子を混合してもよく、乳鉢を用いてシリコン粒子及びリチウムシリケート粒子を混合してもよい。 In the production method of the present disclosure, first, a mixture of silicon particles and lithium silicate particles is prepared. The method for obtaining a mixture of silicon particles and lithium silicate particles is not particularly limited. For example, silicon particles and lithium silicate particles previously pulverized to a desired particle size may be mixed, or silicon particles and lithium silicate particles may be mixed using a mortar.
シリコン粒子とリチウムシリケート粒子との混合割合は特に制限されない。例えば、混合物中のシリコン粒子とリチウムシリケート粒子との合計量に対するシリコン粒子の含有率は３０質量％〜９０質量％であることが好ましく、４０質量％〜８０質量％であることがより好ましく、５０質量％〜７０質量％あることがさらに好ましい。シリコン粒子とリチウムシリケート粒子との合計量に対するシリコン粒子の含有率が８０質量％以下であると、負極の充放電効率が良好となりサイクル特性が向上する傾向にある。シリコン粒子とリチウムシリケート粒子との合計量に対するシリコン粒子の含有率が３０質量％以上であると、負極の充放電容量が向上する傾向にある。 The mixing ratio of the silicon particles and the lithium silicate particles is not particularly limited. For example, the content of the silicon particles with respect to the total amount of the silicon particles and the lithium silicate particles in the mixture is preferably 30% by mass to 90% by mass, more preferably 40% by mass to 80% by mass, and 50% by mass. It is more preferably from% to 70% by mass. When the content of the silicon particles with respect to the total amount of the silicon particles and the lithium silicate particles is 80% by mass or less, the charge / discharge efficiency of the negative electrode tends to be good and the cycle characteristics tend to be improved. When the content of the silicon particles with respect to the total amount of the silicon particles and the lithium silicate particles is 30% by mass or more, the charge / discharge capacity of the negative electrode tends to be improved.
シリコン粒子とリチウムシリケート粒子との混合物は加熱前に所望の形状に成形してもよい。例えば、プレス成形により、ブロック状、ペレット状等の形状に成形してもよい。プレス成形を行う場合の条件は特に制限されず、例えば圧力１００ＭＰａ〜２００ＭＰａで１分〜３分の条件であってもよい。加熱前に成形を行うことによって、溶融したリチウムシリケートが好適にシリコン粒子を被覆しやすい状態にすることができる。 The mixture of silicon particles and lithium silicate particles may be formed into a desired shape before heating. For example, it may be formed into a block shape, a pellet shape, or the like by press molding. The conditions for performing press molding are not particularly limited, and may be, for example, 1 minute to 3 minutes at a pressure of 100 MPa to 200 MPa. By molding before heating, it is possible to make the molten lithium silicate more suitable for coating the silicon particles.
本開示の製造方法では、シリコン粒子とリチウムシリケート粒子との混合物を、リチウムシリケート粒子の溶融温度を超える温度で加熱する。例えばＬｉ２Ｓｉ２Ｏ５の溶融温度は１０３５℃であるため、リチウムシリケートとしてＬｉ２Ｓｉ２Ｏ５を用いる場合には１０３５℃を超える温度で加熱を行う。 In the production method of the present disclosure, a mixture of silicon particles and lithium silicate particles is heated at a temperature exceeding the melting temperature of the lithium silicate particles. For example, since the melting temperature of the Li 2 Si 2 O 5 is 1035 ° C., in the case of using the Li 2 Si 2 O 5 as the lithium silicate performing heating at a temperature exceeding 1035 ° C..
溶融前のシリコン粒子とリチウムシリケート粒子との混合物は、プレス成形等により加圧して成形した状態であっても、ある程度の空隙を含んでいる。本開示の製造方法では、リチウムシリケート粒子を溶融させることにより、負極材としたときの粒子内部の空隙を減らすことができ、高密度のリチウムシリケートでシリコン粒子を被覆することができると考えられる。 The mixture of the silicon particles and the lithium silicate particles before melting contains some voids even in a state of being formed by pressurizing by press molding or the like. In the production method of the present disclosure, it is considered that by melting the lithium silicate particles, the voids inside the particles when used as a negative electrode material can be reduced, and the silicon particles can be coated with high-density lithium silicate.
加熱の温度は、１１００℃〜１４００℃であることが好ましく、１１００℃〜１３００℃であることがより好ましい。加熱温度が上記範囲であると、リチウムシリケートがシリコン粒子を好適に被覆し、サイクル特性の向上効果が好適に得られやすい。 The heating temperature is preferably 1100 ° C to 1400 ° C, more preferably 1100 ° C to 1300 ° C. When the heating temperature is in the above range, the lithium silicate preferably coats the silicon particles, and the effect of improving the cycle characteristics can be preferably obtained.
加熱時間は特に制限されない。リチウムシリケート粒子を溶融するために十分な時間を確保する観点からは、１０分以上であることが好ましく、３０分以上であってもよく、６０分以上であってもよい。製造時間の短縮の観点からは、１８０分以内であることが好ましく、１５０分以内であることがより好ましく、１２０分以内であることがさらに好ましい。 The heating time is not particularly limited. From the viewpoint of securing a sufficient time for melting the lithium silicate particles, it is preferably 10 minutes or more, and may be 30 minutes or more, or 60 minutes or more. From the viewpoint of shortening the production time, it is preferably 180 minutes or less, more preferably 150 minutes or less, and further preferably 120 minutes or less.
加熱の雰囲気は、窒素ガス、アルゴンガス等の不活性ガス雰囲気であることが好ましく、工業的な観点から窒素ガス雰囲気であることが好ましい。 The heating atmosphere is preferably an inert gas atmosphere such as nitrogen gas or argon gas, and is preferably a nitrogen gas atmosphere from an industrial point of view.
加熱後の混合物は解砕してもよく、必要に応じて分級、篩分け等を行ってもよい。解砕方法は特に制限されず、カッターミル、フェーザーミル、ジューサーミキサー等を用いて行うことができる。 The mixture after heating may be crushed, and may be classified, sieved or the like as necessary. The crushing method is not particularly limited, and can be carried out using a cutter mill, a phasor mill, a juicer mixer or the like.
−負極材−
本開示の製造方法により得られる負極材は、負極に用いたときに良好なサイクル特性を示す傾向にある。負極材の粒子内部の空隙率が低く、高密度のリチウムシリケートによってシリコン粒子が被覆されているためと推測される。
-Negative electrode material-
The negative electrode material obtained by the manufacturing method of the present disclosure tends to exhibit good cycle characteristics when used for a negative electrode. It is presumed that the porosity inside the particles of the negative electrode material is low and the silicon particles are covered with high-density lithium silicate.
負極材の内部の空隙率は、１．０％未満であることが好ましく、０．８％以下であることがより好ましく、０．６％以下であることがさらに好ましい。本開示において、負極材の内部の空隙率とは、負極材の粒子断面の断面積における、空隙の占める断面積の割合（％）をいう。空隙率は、粒子断面を走査型電子顕微鏡（ＳＥＭ）で観察することによって測定することができる。例えば、空隙率は、以下のように測定することができる。
（１）日本電子株式会社製のイオンミリング装置（ＩＢ１９５１０ＣＰ型クロスセクションポリッシャ）を用いて、負極材の粒子の断面を露出させる。
（２）露出させた粒子断面をＳＥＭで観察し、粒子断面の総面積に対する空隙の面積割合を測定し、空隙率（空隙面積×１００／粒子断面の総面積）を算出する。
空隙率は粒子１０個についての平均値とする。
なお、上記空隙率は、初回充電前における空隙率とする。
The porosity inside the negative electrode material is preferably less than 1.0%, more preferably 0.8% or less, and even more preferably 0.6% or less. In the present disclosure, the porosity inside the negative electrode material means the ratio (%) of the cross-sectional area occupied by the voids to the cross-sectional area of the particle cross section of the negative electrode material. Porosity can be measured by observing the particle cross section with a scanning electron microscope (SEM). For example, the porosity can be measured as follows.
(1) Using an ion milling device (IB19510CP type cross section polisher) manufactured by JEOL Ltd., the cross section of the particles of the negative electrode material is exposed.
(2) The exposed particle cross section is observed by SEM, the area ratio of the void to the total area of the particle cross section is measured, and the porosity (void area × 100 / total area of the particle cross section) is calculated.
The porosity is an average value for 10 particles.
The porosity is the porosity before the first charge.
本開示の負極材の一実施形態は、上述の本開示の製造方法により得られる。
また、本開示の負極材の一実施形態は、シリコン粒子と前記シリコン粒子を被覆しているリチウムシリケートとを含み、内部の空隙率が１．０％未満である。当該実施形態の構成を有する負極材は、優れたサイクル特性を有する傾向にある。
One embodiment of the negative electrode material of the present disclosure is obtained by the manufacturing method of the present disclosure described above.
Further, one embodiment of the negative electrode material of the present disclosure includes silicon particles and lithium silicate coating the silicon particles, and the internal porosity is less than 1.0%. The negative electrode material having the configuration of the embodiment tends to have excellent cycle characteristics.
本開示の負極材の平均粒子径（Ｄ５０）は特に限定されず、０．５μｍ〜２０μｍであることが好ましく、１μｍ〜１５μｍであることがより好ましい。平均粒子径が０．５μｍ以上であると、比表面積が大きくなりすぎず、リチウムイオン二次電池の初回充放電効率が良好となる傾向にある。さらに、粒子同士の接触が良好に保たれ充放電容量の低下が抑えられる傾向にある。また、表面酸化の影響で純度が低下して充放電容量が低下したり、かさ密度の低下により単位体積あたりの充放電容量が低下したりすることを抑制できる傾向にある。一方、平均粒子径が２０μｍ以下であると、電極面に凸凹が発生することが抑えられる傾向にある。また、粒子表面から内部へのリチウムイオンの拡散距離が長くなりすぎずリチウムイオン二次電池の充放電容量を良好に保つことができる傾向にある。さらに、充放電時の粒子内シリコンの膨張収縮を原因とする粒子割れ、及びこれによるサイクル特性の低下を抑制しやすい傾向にある。 The average particle size (D50) of the negative electrode material of the present disclosure is not particularly limited, and is preferably 0.5 μm to 20 μm, and more preferably 1 μm to 15 μm. When the average particle size is 0.5 μm or more, the specific surface area does not become too large, and the initial charge / discharge efficiency of the lithium ion secondary battery tends to be good. Further, the contact between the particles is kept good, and the decrease in charge / discharge capacity tends to be suppressed. In addition, it tends to be possible to suppress a decrease in purity due to the influence of surface oxidation and a decrease in charge / discharge capacity, and a decrease in charge / discharge capacity per unit volume due to a decrease in bulk density. On the other hand, when the average particle size is 20 μm or less, the occurrence of unevenness on the electrode surface tends to be suppressed. Further, the diffusion distance of lithium ions from the particle surface to the inside does not become too long, and the charge / discharge capacity of the lithium ion secondary battery tends to be kept good. Further, there is a tendency to easily suppress particle cracking caused by expansion and contraction of in-particle silicon during charging and discharging, and deterioration of cycle characteristics due to this.
なお、平均粒子径は以下の方法で測定することができる。
測定試料を界面活性剤（例えば、エソミンＴ／１５、ライオン株式会社製）０．０１質量％水溶液中に入れ、振動撹拌機で分散する。得られた分散液をレーザー回折式粒度分布測定装置（例えば、株式会社島津製作所製ＳＡＬＤ−３０００Ｊ）の試料水槽に入れ、超音波をかけながらポンプで循環させ、レーザー回折式で測定する。得られる粒度分布の体積累積５０％粒子径（Ｄ５０）を平均粒子径とする。測定条件は下記の通りとする。
・光源：赤色半導体レーザー（６９０ｎｍ）
・吸光度：０．１０〜０．１５
・屈折率：２．００〜０．２０
The average particle size can be measured by the following method.
The measurement sample is placed in a 0.01 mass% aqueous solution of a surfactant (for example, Esomin T / 15, manufactured by Lion Corporation) and dispersed with a vibration stirrer. The obtained dispersion is placed in a sample water tank of a laser diffraction type particle size distribution measuring device (for example, SALD-3000J manufactured by Shimadzu Corporation), circulated by a pump while applying ultrasonic waves, and measured by a laser diffraction type. The volume cumulative 50% particle size (D50) of the obtained particle size distribution is defined as the average particle size. The measurement conditions are as follows.
-Light source: Red semiconductor laser (690 nm)
・ Absorbance: 0.10 to 0.15
-Refractive index: 2.00 to 0.20
本開示の負極材の、７７Ｋでの窒素吸着測定より求められる比表面積は、０．１ｍ２／ｇ〜３．０ｍ２／ｇであることが好ましく、０．２ｍ２／ｇ〜２．０ｍ２／ｇであることがより好ましく、０．５ｍ２／ｇ〜１．０ｍ２／ｇであることがさらに好ましい。比表面積が０．１ｍ２／ｇ以上であると、入力特性が良好である傾向にある。また、比表面積が３．０ｍ２／ｇ以下であると、リチウムイオン二次電池の初回不可逆容量の増加を抑制できる傾向にある。なお、窒素吸着での比表面積は、７７Ｋでの窒素吸着測定より得た吸着等温線からＢＥＴ法を用いて求めることができる。 Negative electrode material, the specific surface area determined from nitrogen adsorption measurements at 77K of the present disclosure is preferably 0.1m 2 /g~3.0m 2 / g, 0.2m 2 /g~2.0m 2 more preferably / it is g, and more preferably 0.5m 2 /g~1.0m 2 / g. When the specific surface area is 0.1 m 2 / g or more, the input characteristics tend to be good. Further, when the specific surface area is 3.0 m 2 / g or less, the increase in the initial irreversible capacity of the lithium ion secondary battery tends to be suppressed. The specific surface area of nitrogen adsorption can be determined by using the BET method from the adsorption isotherm obtained from the nitrogen adsorption measurement at 77K.
本開示の一実施形態において、負極材中のリチウムシリケートは結晶構造を有していてもよい。上述の本開示の製造方法では、溶融したリチウムシリケートは冷却の際に結晶化する傾向にある。リチウムシリケートが結晶構造を有しているか否かは、Ｘ線回折装置（例えば、株式会社リガク製、全自動多目的水平型Ｘ線回折装置（Ｓｍａｒｔ Ｌａｂ））を用いて確認することができる。 In one embodiment of the present disclosure, the lithium silicate in the negative electrode material may have a crystal structure. In the production method of the present disclosure described above, the molten lithium silicate tends to crystallize upon cooling. Whether or not the lithium silicate has a crystal structure can be confirmed by using an X-ray diffractometer (for example, a fully automatic multipurpose horizontal X-ray diffractometer (Smart Lab) manufactured by Rigaku Co., Ltd.).
本開示の負極材の粒子中のリチウムシリケートの形状は粒子状ではないことが好ましい。上述の本開示の製造方法では、製造された負極材の粒子中のリチウムシリケートは原料となった粒子の形状を有しておらず、リチウムシリケートの溶融物が冷却されてシリコン粒子を覆った構造をとっている。 It is preferable that the shape of the lithium silicate in the particles of the negative electrode material of the present disclosure is not particulate. In the manufacturing method of the present disclosure described above, the lithium silicate in the particles of the manufactured negative electrode material does not have the shape of the raw material particles, and the melt of the lithium silicate is cooled to cover the silicon particles. I'm taking.
本開示の負極材は、炭素で被覆されていてもよい。負極材が炭素で被覆されていると、負極材の電解質との反応が抑制され、負極のサイクル特性が向上する傾向にある。なお、本開示の負極材はサイクル特性に優れているため、炭素で被覆されていなくてもよい。 The negative electrode material of the present disclosure may be coated with carbon. When the negative electrode material is coated with carbon, the reaction of the negative electrode material with the electrolyte is suppressed, and the cycle characteristics of the negative electrode tend to be improved. Since the negative electrode material of the present disclosure has excellent cycle characteristics, it does not have to be coated with carbon.
負極材が炭素で被覆されている場合、炭素は、上述のように作製された負極材（ここでは、上述のように作製されたシリコン及びリチウムシリケートを含有する粒子をいう）の表面全体に存在していてもよく、表面の一部のみに存在していてもよい。以下、上述のように作製されたシリコン及びリチウムシリケートを含有する粒子の表面の少なくとも一部に存在するように形成された炭素の層を、炭素被覆層ともいう。 When the negative electrode material is coated with carbon, carbon is present on the entire surface of the negative electrode material prepared as described above (here, the particles containing silicon and lithium silicate prepared as described above). It may be present, or it may be present only on a part of the surface. Hereinafter, the carbon layer formed so as to be present on at least a part of the surface of the silicon and lithium silicate-containing particles produced as described above is also referred to as a carbon coating layer.
シリコン及びリチウムシリケートを含有する粒子に対する炭素の比率は特に限定されず、質量比で０．００１〜０．３であることが好ましい。シリコン及びリチウムシリケートを含有する粒子に対する炭素被覆層の比率（質量比）が０．００１以上であると、リチウムイオン二次電池としたときに良好な寿命特性、及び充放電容量が得られる傾向にあり、０．３以下であると、リチウムイオン二次電池としたときに良好な初回充放電効率及びエネルギー密度が得られる傾向にある。シリコン及びリチウムシリケートを含有する粒子に対する炭素被覆層の比率は、シリコン及びリチウムシリケートを含有する粒子の質量、並びに炭素被覆層となる炭素前駆体の質量及び炭素前駆体の炭化率より算出することができる。 The ratio of carbon to the particles containing silicon and lithium silicate is not particularly limited, and the mass ratio is preferably 0.001 to 0.3. When the ratio (mass ratio) of the carbon coating layer to the particles containing silicon and lithium silicate is 0.001 or more, good life characteristics and charge / discharge capacity tend to be obtained when the lithium ion secondary battery is used. If it is 0.3 or less, good initial charge / discharge efficiency and energy density tend to be obtained when a lithium ion secondary battery is used. The ratio of the carbon coating layer to the particles containing silicon and lithium silicate can be calculated from the mass of the particles containing silicon and lithium silicate, the mass of the carbon precursor to be the carbon coating layer, and the carbonization rate of the carbon precursor. it can.
炭素被覆層は、例えば、熱処理により炭素質を残す有機化合物（炭素前駆体ともいう）を上記シリコン及びリチウムシリケートを含有する粒子の表面に付着させた後、焼成することで形成してもよい。 The carbon coating layer may be formed, for example, by adhering an organic compound (also referred to as a carbon precursor) that leaves carbonaceous material by heat treatment to the surface of the particles containing silicon and lithium silicate, and then calcining the particles.
シリコン及びリチウムシリケートを含有する粒子の表面に有機化合物を付着させる方法としては、特に制限はなく、有機化合物を溶媒に溶解、又は分散させた混合溶液にシリコン及びリチウムシリケートを含有する粒子を分散して混合した後、溶媒を除去する湿式方式、シリコン及びリチウムシリケートを含有する粒子と有機化合物を固体同士で混合し、その混合物に力学エネルギーを加え付着させる乾式方式、ＣＶＤ法等の気相法などが挙げられる。 The method of adhering the organic compound to the surface of the particles containing silicon and lithium silicate is not particularly limited, and the particles containing silicon and lithium silicate are dispersed in a mixed solution in which the organic compound is dissolved or dispersed in a solvent. A wet method that removes the solvent after mixing, a dry method that mixes particles containing silicon and lithium silicate and an organic compound with each other, and applies mechanical energy to the mixture to attach them, a vapor phase method such as a CVD method, etc. Can be mentioned.
シリコン及びリチウムシリケートを含有する粒子の表面に有機化合物を付着させる場合の有機化合物に特に制限はなく、熱可塑性樹脂、熱硬化性樹脂等の高分子化合物などを用いることができる。例えば、熱可塑性樹脂を用いる場合は、液相経由で炭素化し、比表面積の比較的小さな炭素被覆層が生成する。この炭素被覆層がシリコン及びリチウムシリケートを含有する粒子の表面に存在すると負極材の比表面積も比較的小さくなり、結果としてリチウムイオン二次電池の初回不可逆容量が小さくなる傾向があるため、好ましい。有機化合物は１種を単独で用いてもよく、２種以上を併用してもよい。 The organic compound when the organic compound is attached to the surface of the particles containing silicon and lithium silicate is not particularly limited, and a polymer compound such as a thermoplastic resin or a thermosetting resin can be used. For example, when a thermoplastic resin is used, it is carbonized via the liquid phase to form a carbon coating layer having a relatively small specific surface area. When this carbon coating layer is present on the surface of particles containing silicon and lithium silicate, the specific surface area of the negative electrode material is also relatively small, and as a result, the initial irreversible capacity of the lithium ion secondary battery tends to be small, which is preferable. One type of organic compound may be used alone, or two or more types may be used in combination.
熱可塑性樹脂を用いる場合の熱可塑性樹脂は特に限定されず、エチレンヘビーエンドピッチ、原油ピッチ、コールタールピッチ、石炭ピッチ、アスファルト分解ピッチ、ポリ塩化ビニル等を熱分解して生成するピッチ、ナフタレン等を超強酸存在下で重合させて作製される合成ピッチなどを使用してもよい。また、熱可塑性樹脂として、ポリ塩化ビニル、ポリビニルアルコール、ポリ酢酸ビニル、ポリビニルブチラール等を用いてもよい。また、デンプン、セルロース等の天然物を用いてもよい。熱可塑性樹脂は１種を単独で用いてもよく、２種以上を併用してもよい。 When a thermoplastic resin is used, the thermoplastic resin is not particularly limited, and is such as ethylene heavy end pitch, crude oil pitch, coal tar pitch, coal pitch, asphalt decomposition pitch, pitch produced by thermal decomposition of polyvinyl chloride, etc. May be used, such as a synthetic pitch produced by polymerizing in the presence of a super strong acid. Further, as the thermoplastic resin, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral and the like may be used. In addition, natural products such as starch and cellulose may be used. One type of thermoplastic resin may be used alone, or two or more types may be used in combination.
有機化合物を溶解又は分散する溶媒は特に限定されない。溶媒は１種を単独で用いてもよく、２種以上を併用してもよい。被覆効果を向上させるため、界面活性剤、分散材等を添加することでシリコン粒子の表面と有機化合物の親和性を向上させてもよい。 The solvent that dissolves or disperses the organic compound is not particularly limited. One type of solvent may be used alone, or two or more types may be used in combination. In order to improve the coating effect, the affinity between the surface of the silicon particles and the organic compound may be improved by adding a surfactant, a dispersant or the like.
有機化合物がピッチ類の場合には、溶媒としてテトラヒドロフラン、トルエン、キシレン、ベンゼン、キノリン、ピリジン、石炭乾留において生成する比較的低沸点の液状物の混合物（クレオソート油）等を使用してもよい。また、有機化合物がポリ塩化ビニルの場合には、溶媒としてテトラヒドロフラン、シクロヘキサノン、ニトロベンゼン等を使用してもよい。有機化合物がポリ酢酸ビニル、ポリビニルブチラール等の場合には、溶媒としてアルコール類、エステル類、ケトン類等を使用してもよい。有機化合物がポリビニルアルコールの場合には、溶媒として水等を使用してもよい。なお、水を溶媒とする場合には、溶媒中でのシリコン及びリチウムシリケートを含有する粒子の混合又は分散を促進させ、有機化合物とシリコン及びリチウムシリケートを含有する粒子との密着性を向上させるため、界面活性剤を添加してもよい。 When the organic compound is pitch, tetrahydrofuran, toluene, xylene, benzene, quinoline, pyridine, a mixture of liquids having a relatively low boiling point produced by carbonization of coal (creosort oil), or the like may be used as the solvent. .. When the organic compound is polyvinyl chloride, tetrahydrofuran, cyclohexanone, nitrobenzene or the like may be used as the solvent. When the organic compound is polyvinyl acetate, polyvinyl butyral or the like, alcohols, esters, ketones or the like may be used as the solvent. When the organic compound is polyvinyl alcohol, water or the like may be used as the solvent. When water is used as the solvent, in order to promote the mixing or dispersion of the particles containing silicon and lithium silicate in the solvent and to improve the adhesion between the organic compound and the particles containing silicon and lithium silicate. , Surfactant may be added.
溶媒の除去は、常圧又は減圧雰囲気で加熱することによって行ってもよい。溶媒除去の際の温度は、雰囲気が大気の場合、２００℃以下であることが好ましい。除去温度が２００℃以下であると、雰囲気中の酸素と有機化合物及び溶媒（特にクレオソート油を用いる場合）の反応が抑えられ、焼成によって生成する炭素量が変動することを抑制できる傾向にある。また、多孔質化が抑制されることにより、負極材として所望の特性を発現しやすい傾向にある。 The solvent may be removed by heating in a normal pressure or reduced pressure atmosphere. When the atmosphere is the atmosphere, the temperature at the time of removing the solvent is preferably 200 ° C. or lower. When the removal temperature is 200 ° C. or lower, the reaction between oxygen in the atmosphere and the organic compound and the solvent (especially when creosote oil is used) is suppressed, and the amount of carbon produced by firing tends to be suppressed from fluctuating. .. Further, by suppressing the porosity, the negative electrode material tends to easily exhibit desired characteristics.
また、有機化合物の付着したシリコン及びリチウムシリケートを含有する粒子の焼成条件は、当該有機化合物の炭素化率を考慮して適宜決定すればよく、特に限定されない。非酸化性雰囲気下、好ましくは、７００℃〜１０００℃、より好ましくは、７００℃〜９００℃の範囲で焼成することが好ましい。焼成温度が７００℃以上であると、リチウムイオン二次電池の初回不可逆容量を抑えられる傾向にあり、一方、焼成温度が１０００℃以下であると、生産コストの増加を抑えられる傾向にある。
非酸化性雰囲気下としては、窒素、アルゴン、ヘリウム等の不活性ガス雰囲気下、真空雰囲気下、循環された燃焼排ガス雰囲気下などが挙げられる。
Further, the firing conditions of the particles containing silicon and lithium silicate to which the organic compound is attached may be appropriately determined in consideration of the carbonization rate of the organic compound, and are not particularly limited. In a non-oxidizing atmosphere, firing is preferably in the range of 700 ° C. to 1000 ° C., more preferably 700 ° C. to 900 ° C. When the firing temperature is 700 ° C. or higher, the initial irreversible capacity of the lithium ion secondary battery tends to be suppressed, while when the firing temperature is 1000 ° C. or lower, the increase in production cost tends to be suppressed.
Examples of the non-oxidizing atmosphere include an atmosphere of an inert gas such as nitrogen, argon, and helium, a vacuum atmosphere, and a circulated combustion exhaust gas atmosphere.
また、焼成に先だって、有機化合物の付着したシリコン及びリチウムシリケートを含有する粒子を１５０℃〜３００℃の温度で加熱処理してもよい。例えば、有機化合物としてポリビニルアルコールを用いる場合、このような加熱処理により炭素化率を増加させることができる傾向にある。 Further, prior to firing, particles containing silicon and lithium silicate to which an organic compound is attached may be heat-treated at a temperature of 150 ° C. to 300 ° C. For example, when polyvinyl alcohol is used as the organic compound, the carbonization rate tends to be increased by such heat treatment.
上述のように炭素で被覆された粒子に対して、必要に応じて、解砕処理、分級処理、又は篩分け処理を施し、本開示の負極材を得てもよい。 The negative electrode material of the present disclosure may be obtained by subjecting the carbon-coated particles as described above to a crushing treatment, a classification treatment, or a sieving treatment, if necessary.
本開示の負極材は、本開示の負極材とは異なる負極材と混合して負極に用いてもよい。充放電容量とサイクル特性を好適に両立する観点からは、本開示の負極材を、全負極材に対して０．５質量％〜２０質量％、より好ましくは１質量％〜１５質量％、さらに好ましくは３質量％〜１０質量％混合して負極に用いてもよい。 The negative electrode material of the present disclosure may be mixed with a negative electrode material different from the negative electrode material of the present disclosure and used for the negative electrode. From the viewpoint of preferably achieving both charge / discharge capacity and cycle characteristics, the negative electrode material of the present disclosure is 0.5% by mass to 20% by mass, more preferably 1% by mass to 15% by mass, and further, with respect to the total negative electrode material. Preferably, 3% by mass to 10% by mass may be mixed and used for the negative electrode.
本開示の負極材とは異なる負極材としては、例えば、本開示の負極材とは異なる、シリコン単体、シリコン合金、シリコンと二酸化ケイ素との複合体等のシリコン系粒子；黒鉛質粒子、非晶質炭素粒子等の炭素質材料；酸化錫等の金属酸化物；金属複合酸化物；リチウム単体；リチウムアルミニウム合金等のリチウム合金；錫等のリチウムと合金形成可能な材料などの粒子、が挙げられる。負極材は１種を単独で用いてもよく、２種以上を組み合わせて用いてもよい。
金属複合酸化物としては、リチウムイオンを吸蔵及び放出可能なものであれば特に制限はなく、放電特性の観点からは、チタン、リチウム、又はチタン及びリチウムの双方を含有する金属酸化物が好ましい。
充放電容量とサイクル特性を好適に両立する観点から、本開示の負極材及び必要に応じて用いられる本開示の負極材とは異なるシリコン系粒子の合計含有率は、負極に用いられる全負極材に対して、０．５質量％〜２０質量％であることが好ましく、１質量％〜１５質量％であることがより好ましく、３質量％〜１０質量％であることがさらに好ましい。
Examples of the negative electrode material different from the negative electrode material of the present disclosure include silicon-based particles such as elemental silicon, a silicon alloy, and a composite of silicon and silicon dioxide, which are different from the negative electrode material of the present disclosure; Carbonaceous materials such as carbon particles; metal oxides such as tin oxide; metal composite oxides; elemental lithium; lithium alloys such as lithium aluminum alloys; particles such as materials capable of forming alloys with lithium such as tin. .. One type of negative electrode material may be used alone, or two or more types may be used in combination.
The metal composite oxide is not particularly limited as long as it can occlude and release lithium ions, and from the viewpoint of discharge characteristics, titanium, lithium, or a metal oxide containing both titanium and lithium is preferable.
From the viewpoint of achieving both charge / discharge capacity and cycle characteristics, the total content of silicon-based particles different from the negative electrode material of the present disclosure and the negative electrode material of the present disclosure used as needed is the total negative electrode material used for the negative electrode. On the other hand, it is preferably 0.5% by mass to 20% by mass, more preferably 1% by mass to 15% by mass, and further preferably 3% by mass to 10% by mass.
≪リチウムイオン二次電池用負極≫
本開示におけるリチウムイオン二次電池用負極は、本開示の負極材を含有する。
一実施形態において、リチウムイオン二次電池用負極は、集電体と、前記集電体上に形成される本開示の負極材を含有する負極合剤層と、を含む。
一実施形態において、リチウムイオン二次電池用負極は、本開示の負極材及び必要に応じて用いられるその他の負極材、並びに有機結着剤を溶媒とともに撹拌機、ボールミル、スーパーサンドミル、加圧ニーダー等の分散装置により混練して負極材スラリーを調製し、これを集電体に塗布して負極層を形成する、又は、ペースト状の負極材スラリーをシート状、ペレット状等の形状に成形し、これを集電体と一体化することで得ることができる。
≪Negative electrode for lithium ion secondary battery≫
The negative electrode for a lithium ion secondary battery in the present disclosure contains the negative electrode material of the present disclosure.
In one embodiment, the negative electrode for a lithium ion secondary battery includes a current collector and a negative electrode mixture layer containing the negative electrode material of the present disclosure formed on the current collector.
In one embodiment, the negative electrode for a lithium ion secondary battery is a stirrer, a ball mill, a super sand mill, a pressurized kneader, in which the negative electrode material of the present disclosure and other negative electrode materials used as needed, and an organic binder are mixed with a solvent. A negative electrode material slurry is prepared by kneading with a disperser such as, and this is applied to a current collector to form a negative electrode layer, or a paste-like negative electrode material slurry is formed into a sheet shape, a pellet shape, or the like. , This can be obtained by integrating with the current collector.
上記有機結着剤は特に限定されず、スチレン−ブタジエン共重合体、メチル（メタ）アクリレート、エチル（メタ）アクリレート、ブチル（メタ）アクリレート、（メタ）アクリロニトリル、ヒドロキシエチル（メタ）アクリレート等のエチレン性不飽和カルボン酸エステル；アクリル酸、メタクリル酸、イタコン酸、フマル酸、マレイン酸等のエチレン性不飽和カルボン酸；ポリフッ化ビニリデン、ポリエチレンオキサイド、ポリエピクロロヒドリン、ポリフォスファゼン、ポリアクリロニトリル等のイオン導電性の大きな高分子化合物などが挙げられる。有機結着剤は１種を単独で用いてもよく、２種以上を併用してもよい。有機結着剤の含有量は特に限定されず、負極材と有機結着剤の合計１００質量部に対して１質量部〜２０質量部含有することが好ましい。 The organic binder is not particularly limited, and ethylene such as a styrene-butadiene copolymer, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile, and hydroxyethyl (meth) acrylate Sexual unsaturated carboxylic acid ester; ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid; Examples thereof include polymer compounds having high ionic conductivity. One type of organic binder may be used alone, or two or more types may be used in combination. The content of the organic binder is not particularly limited, and is preferably 1 part by mass to 20 parts by mass with respect to 100 parts by mass of the total of the negative electrode material and the organic binder.
負極材スラリーには、粘度を調整するための増粘剤を添加してもよい。増粘剤は特に限定されず、カルボキシメチルセルロース、メチルセルロース、ヒドロキシメチルセルロース、エチルセルロース、ポリビニルアルコール、ポリアクリル酸（又はその塩）、酸化スターチ、リン酸化スターチ、カゼイン等を使用することができる。増粘剤は１種を単独で用いてもよく、２種以上を併用してもよい。 A thickener for adjusting the viscosity may be added to the negative electrode material slurry. The thickener is not particularly limited, and carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid (or a salt thereof), oxidized starch, phosphorylated starch, casein and the like can be used. One type of thickener may be used alone, or two or more types may be used in combination.
また、上記負極材スラリーには、導電補助材を混合してもよい。導電補助材は特に限定されず、カーボンブラック、グラファイト、アセチレンブラック、導電性を示す酸化物又は窒化物等が挙げられる。導電助剤の使用量は、負極材の１質量％〜１５質量％程度としてよい。 Further, the conductive auxiliary material may be mixed with the negative electrode material slurry. The conductive auxiliary material is not particularly limited, and examples thereof include carbon black, graphite, acetylene black, and oxides or nitrides exhibiting conductivity. The amount of the conductive auxiliary agent used may be about 1% by mass to 15% by mass of the negative electrode material.
集電体の材質及び形状は特に限定されず、アルミニウム、銅、ニッケル、チタン、ステンレス鋼等を、箔状、穴開け箔状、メッシュ状等にした帯状の集電体を用いることができる。また、ポーラスメタル（発泡メタル）、カーボンペーパー等の多孔性材料も使用可能である。 The material and shape of the current collector are not particularly limited, and a strip-shaped current collector made of aluminum, copper, nickel, titanium, stainless steel, or the like in the form of a foil, a perforated foil, a mesh, or the like can be used. Further, porous materials such as porous metal (foam metal) and carbon paper can also be used.
負極材スラリーを集電体に塗布してリチウムイオン二次電池用負極を得る場合、負極材スラリーを集電体に塗布する方法は特に限定されず、メタルマスク印刷法、静電塗装法、ディップコート法、スプレーコート法、ロールコート法、ドクターブレード法、グラビアコート法、スクリーン印刷法等の公知の方法が挙げられる。塗布後は、必要に応じて平板プレス、カレンダーロール等による圧延処理を行ってもよい。
負極材スラリーをシート状、ペレット状等の形状に成形し、これを集電体と一体化してリチウムイオン二次電池用負極を得る場合、シート状、ペレット状等の形状に成形された負極材スラリーと集電体との一体化の方法は特に限定されず、ロール、プレス、又はこれらの組み合わせ等の公知の方法により行ってよい。
When the negative electrode material slurry is applied to the current collector to obtain a negative electrode for a lithium ion secondary battery, the method of applying the negative electrode material slurry to the current collector is not particularly limited, and a metal mask printing method, an electrostatic coating method, or a dip Known methods such as a coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, and a screen printing method can be mentioned. After coating, a flat plate press, a calender roll, or the like may be used for rolling, if necessary.
Negative electrode material When a slurry is molded into a sheet or pellet shape and integrated with a current collector to obtain a negative electrode for a lithium ion secondary battery, the negative electrode material is molded into a sheet or pellet shape. The method of integrating the slurry and the current collector is not particularly limited, and a known method such as a roll, a press, or a combination thereof may be used.
≪リチウムイオン二次電池≫
本開示のリチウムイオン二次電池は、本開示の負極を備える。リチウムイオン二次電池は、例えば、負極と正極とをセパレータを介して対向して配置し、電解液を注入することにより得ることができる。
≪Lithium-ion secondary battery≫
The lithium ion secondary battery of the present disclosure includes the negative electrode of the present disclosure. A lithium ion secondary battery can be obtained, for example, by arranging a negative electrode and a positive electrode facing each other via a separator and injecting an electrolytic solution.
正極は、上記負極と同様にして、集電体表面上に正極層を形成することで得ることができる。この場合の集電体はアルミニウム、チタン、ステンレス鋼等の金属又は合金を、箔状、穴開け箔状、メッシュ状等にした帯状の集電体を用いることができる。 The positive electrode can be obtained by forming a positive electrode layer on the surface of the current collector in the same manner as the negative electrode. In this case, as the current collector, a strip-shaped current collector obtained by forming a metal or alloy such as aluminum, titanium, or stainless steel into a foil shape, a perforated foil shape, a mesh shape, or the like can be used.
上記正極層に用いる正極材料は特に限定されず、例えば、リチウムイオンをドーピング若しくはインターカレーション可能な金属化合物、金属酸化物、金属硫化物、又は導電性高分子材料を用いてよい。例えば、コバルト酸リチウム（ＬｉＣｏＯ２）、ニッケル酸リチウム（ＬｉＮｉＯ２）、マンガン酸リチウム（ＬｉＭｎＯ２）、及びこれらの複酸化物（ＬｉＣｏｘＮｉｙＭｎｚＯ２、Ｘ＋Ｙ＋Ｚ＝１）、リチウムマンガンスピネル（ＬｉＭｎ２Ｏ４）、リチウムバナジウム化合物、Ｖ２Ｏ５、Ｖ６Ｏ１３、ＶＯ２、ＭｎＯ２、ＴｉＯ２、ＭｏＶ２Ｏ８、ＴｉＳ２、Ｖ２Ｓ５、ＶＳ２、ＭｏＳ２、ＭｏＳ３、Ｃｒ３Ｏ８、Ｃｒ２Ｏ５、オリビン型ＬｉＭＰＯ４（ＭはＣｏ、Ｎｉ、Ｍｎ、又はＦｅを表す）、ポリアセチレン、ポリアニリン、ポリピロール、ポリチオフェン、ポリアセン等の導電性ポリマー、多孔質炭素などを用いることができる。正極材料は１種を単独で用いてもよく、２種以上を併用してもよい。 The positive electrode material used for the positive electrode layer is not particularly limited, and for example, a metal compound capable of doping or intercalating lithium ions, a metal oxide, a metal sulfide, or a conductive polymer material may be used. For example, lithium cobalt oxide (LiCoO 2), lithium nickelate (LiNiO 2), lithium manganate (LiMnO 2), and these mixed oxide (LiCo x Ni y Mn z O 2, X + Y + Z = 1), lithium manganese spinel (LiMn 2 O 4 ), Lithium vanadium compound, V 2 O 5 , V 6 O 13 , VO 2 , MnO 2 , TiO 2 , MoV 2 O 8 , TiS 2 , V 2 S 5 , VS 2 , MoS 2 , MoS 3 , Cr 3 O 8 , Cr 2 O 5 , olivine type LiMPO 4 (M stands for Co, Ni, Mn, or Fe), polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, and other conductive polymers, porous carbon, etc. Can be used. One type of positive electrode material may be used alone, or two or more types may be used in combination.
セパレータとしては、例えば、ポリエチレン、ポリプロピレン等のポリオレフィンを主成分とした不織布、クロス、微孔フィルム又はそれらを組み合わせたものが挙げられる。なお、作製するリチウムイオン二次電池の正極と負極が直接接触しない構造である場合は、セパレータを使用する必要はない。 Examples of the separator include non-woven fabrics containing polyolefins such as polyethylene and polypropylene as main components, cloths, micropore films, and combinations thereof. If the structure is such that the positive electrode and the negative electrode of the lithium ion secondary battery to be manufactured do not come into direct contact with each other, it is not necessary to use a separator.
電解液としては、例えば、ＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＡｓＦ６、ＬｉＢＦ４、ＬｉＳＯ３ＣＦ３等のリチウム塩を、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、ビニレンカーボネート、シクロペンタノン、スルホラン、３−メチルスルホラン、２，４−ジメチルスルホラン、３−メチル−１，３−オキサゾリジン−２−オン、γ−ブチロラクトン、ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネート、メチルプロピルカーボネート、ブチルメチルカーボネート、エチルプロピルカーボネート、ブチルエチルカーボネート、ジプロピルカーボネート、１，２−ジメトキシエタン、テトラヒドロフラン、２−メチルテトラヒドロフラン、１，３−ジオキソラン、酢酸メチル、酢酸エチル等の単体又は２成分以上の混合物を非水系溶剤に溶解した、いわゆる有機電解液であってもよい。 Examples of the electrolytic solution include lithium salts such as LiClO 4 , LiPF 6 , LiAsF 6 , LiBF 4 , LiSO 3 CF 3 , ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, sulfolane, and 3-methyl. Sulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidine-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl So-called ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate and the like alone or a mixture of two or more components dissolved in a non-aqueous solvent. It may be an organic electrolyte.
また、電解液としては、リチウム塩水和物（常温溶融水和物（ハイドレートメルト））等の水系溶媒を使用してもよい。 Further, as the electrolytic solution, an aqueous solvent such as lithium salt hydrate (normal temperature melt hydrate (hydrate melt)) may be used.
本開示のリチウムイオン二次電池の構造は、特に限定されない。例えば、正極及び負極と、必要に応じて設けられるセパレータとを、扁平渦巻状に巻回して巻回式極板群としたり、これらを平板状として積層して積層式極板群としたりし、これら極板群を外装体中に封入した構造が挙げられる。 The structure of the lithium ion secondary battery of the present disclosure is not particularly limited. For example, the positive electrode and the negative electrode and the separator provided as needed may be wound in a flat spiral shape to form a wound electrode plate group, or these may be laminated as a flat plate to form a laminated electrode plate group. Examples thereof include a structure in which these electrode plates are enclosed in an exterior body.
本開示のリチウムイオン二次電池の形状は特に限定されず、ペーパー型電池、ボタン型電池、コイン型電池、積層型電池、円筒型電池等として使用することができる。 The shape of the lithium ion secondary battery of the present disclosure is not particularly limited, and can be used as a paper type battery, a button type battery, a coin type battery, a laminated type battery, a cylindrical type battery, or the like.
本開示のリチウムイオン二次電池の用途は特に限定されず、電気自動車、パワーツール等の用途が挙げられる。 The application of the lithium ion secondary battery of the present disclosure is not particularly limited, and examples thereof include applications such as electric vehicles and power tools.
次に、下記の実施例により本開示の実施形態をさらに詳しく説明するが、これらの実施例は本発明を制限するものではない。 Next, the embodiments of the present disclosure will be described in more detail with reference to the following examples, but these examples do not limit the present invention.
〔負極材の作製〕
（比較例１）
乾式粉砕法によって作製された粒径Ｄ５０＝８００ｎｍのナノシリコン粒子を用いた。乾式粉砕法によって作製された粒径Ｄ５０＝８００ｎｍのナノシリコン粒子を、Ｄ５０＝２５μｍのリチウムシリケート（Ｌｉ２Ｓｉ２Ｏ５）粒子と２０分乳鉢混合し、負極活物質を得た。
[Preparation of negative electrode material]
(Comparative Example 1)
Nanosilicon particles having a particle size of D50 = 800 nm produced by a dry pulverization method were used. Nanosilicon particles having a particle size of D50 = 800 nm produced by a dry pulverization method were mixed with lithium silicate (Li 2 Si 2 O 5 ) particles having a diameter of D50 = 25 μm in a mortar for 20 minutes to obtain a negative electrode active material.
（実施例１）
熱プラズマ法によって作製された粒径Ｄ５０＝８００ｎｍのナノシリコン粒子と、Ｄ５０＝２５μｍのリチウムシリケート（Ｌｉ２Ｓｉ２Ｏ５）粒子と、を質量比６０：４０となるように計量し、２０分間乳鉢混合し負極活物質を得た。これらの混合粒子に対して面圧１５０ＭＰａの条件で一軸プレスを３分間行い、円盤状のペレットとした。その後窒素不活性雰囲気下で、１１００℃、２時間の熱処理を行った。その後、熱処理後サンプルをメディアン径がＤ５０＝約１０μｍとなるように、乳鉢粉砕及び分級し、負極材を得た。
(Example 1)
Nanosilicon particles having a particle size of D50 = 800 nm and lithium silicate (Li 2 Si 2 O 5 ) particles having a particle size of D50 = 25 μm produced by the thermal plasma method were weighed so as to have a mass ratio of 60:40 for 20 minutes. The mixture was mixed in a dairy pot to obtain a negative electrode active material. The mixed particles were uniaxially pressed for 3 minutes under the condition of a surface pressure of 150 MPa to obtain disc-shaped pellets. Then, the heat treatment was carried out at 1100 ° C. for 2 hours in a nitrogen-inert atmosphere. Then, after the heat treatment, the sample was crushed and classified in a mortar so that the median diameter was D50 = about 10 μm to obtain a negative electrode material.
（実施例２）
熱プラズマ法によって作製された粒径Ｄ５０＝８００ｎｍのナノシリコン粒子と、Ｄ５０＝２５μｍのリチウムシリケート（Ｌｉ２Ｓｉ２Ｏ５）粒子と、を質量比６０：４０となるように計量し、２０分間乳鉢混合し、負極活物質を得た。これらの混合粒子に対して面圧１５０ＭＰａの条件で一軸プレスを３分間行い、円盤状のペレットとした。その後窒素不活性雰囲気下で、１１００℃、２時間の熱処理を行った。その後、熱処理後サンプルをメディアン径がＤ５０＝約１０μｍとなるように、乳鉢粉砕及び分級し、負極活物質を得た。その後、得られた負極活物質を石炭ピッチと混合し、窒素不活性雰囲気下、９５０℃で焼成することにより、炭素被覆層を設けた負極材を得た。
(Example 2)
Nanosilicon particles having a particle size of D50 = 800 nm and lithium silicate (Li 2 Si 2 O 5 ) particles having a particle size of D50 = 25 μm produced by the thermal plasma method were weighed so as to have a mass ratio of 60:40 for 20 minutes. The mixture was mixed in a dairy pot to obtain a negative electrode active material. The mixed particles were uniaxially pressed for 3 minutes under the condition of a surface pressure of 150 MPa to obtain disc-shaped pellets. Then, the heat treatment was carried out at 1100 ° C. for 2 hours in a nitrogen-inert atmosphere. Then, after the heat treatment, the sample was crushed and classified in a mortar so that the median diameter was D50 = about 10 μm to obtain a negative electrode active material. Then, the obtained negative electrode active material was mixed with coal pitch and calcined at 950 ° C. in a nitrogen-inactive atmosphere to obtain a negative electrode material provided with a carbon coating layer.
（実施例３）
熱プラズマ法によって作製された粒径Ｄ５０＝８００ｎｍのナノシリコン粒子と、Ｄ５０＝２５μｍのリチウムシリケート（Ｌｉ２Ｓｉ２Ｏ５）粒子と、を質量比７０：３０となるように計量し、２０分間乳鉢混合し、負極活物質を得た。これらの混合粒子に対して面圧１５０ＭＰａの条件で一軸プレスを３分間行い、円盤状のペレットとした。その後窒素不活性雰囲気下で、１１００℃、２時間の熱処理を行った。その後、熱処理後サンプルをメディアン径がＤ５０＝約１０μｍとなるように、乳鉢粉砕及び分級し、負極材を得た。
(Example 3)
Nanosilicon particles having a particle size of D50 = 800 nm and lithium silicate (Li 2 Si 2 O 5 ) particles having a particle size of D50 = 25 μm produced by the thermal plasma method were weighed so as to have a mass ratio of 70:30 for 20 minutes. The mixture was mixed in a dairy pot to obtain a negative electrode active material. The mixed particles were uniaxially pressed for 3 minutes under the condition of a surface pressure of 150 MPa to obtain disc-shaped pellets. Then, the heat treatment was carried out at 1100 ° C. for 2 hours in a nitrogen-inert atmosphere. Then, after the heat treatment, the sample was crushed and classified in a mortar so that the median diameter was D50 = about 10 μm to obtain a negative electrode material.
（実施例４）
熱プラズマ法によって作製された粒径Ｄ５０＝８００ｎｍのナノシリコン粒子と、Ｄ５０＝２５μｍのリチウムシリケート（Ｌｉ２Ｓｉ２Ｏ５）粒子と、を質量比７０：３０となるように計量し、２０分間乳鉢混合し、負極活物質を得た。これらの混合粒子に対して面圧１５０ＭＰａの条件で一軸プレスを３分間行い、円盤状のペレットとした。その後窒素不活性雰囲気下で、１１００℃、２時間の熱処理を行った。その後、熱処理後サンプルをメディアン径がＤ５０＝約１０μｍとなるように、乳鉢粉砕及び分級し、負極活物質を得た。その後、得られた負極活物質を石炭ピッチと混合し、窒素不活性雰囲気下、９５０℃で焼成することにより、炭素被覆層を設けた負極材を得た。
(Example 4)
Nanosilicon particles having a particle size of D50 = 800 nm and lithium silicate (Li 2 Si 2 O 5 ) particles having a particle size of D50 = 25 μm produced by the thermal plasma method were weighed so as to have a mass ratio of 70:30 for 20 minutes. The mixture was mixed in a dairy pot to obtain a negative electrode active material. The mixed particles were uniaxially pressed for 3 minutes under the condition of a surface pressure of 150 MPa to obtain disc-shaped pellets. Then, the heat treatment was carried out at 1100 ° C. for 2 hours in a nitrogen-inert atmosphere. Then, after the heat treatment, the sample was crushed and classified in a mortar so that the median diameter was D50 = about 10 μm to obtain a negative electrode active material. Then, the obtained negative electrode active material was mixed with coal pitch and calcined at 950 ° C. in a nitrogen-inactive atmosphere to obtain a negative electrode material provided with a carbon coating layer.
上記の実施例及び比較例で得られた負極材を用いて、物性及び電気的特性を下記の要領で測定した。測定結果を表１に示す。 Using the negative electrode materials obtained in the above Examples and Comparative Examples, the physical properties and electrical properties were measured as follows. The measurement results are shown in Table 1.
［空隙率］
得られた負極材試料１ｇをポリフッ化ビニリデンと質量比２：１で混合し、銅箔に塗布し、１０５℃で乾燥した。得られた塗工箔に対して、日本電子株式会社製のイオンミリング装置（ＩＢ１９５１０ＣＰ型クロスセクションポリッシャ）を用いて、断面処理を行い、負極材粒子の断面を露出させた。露出させた粒子断面をＳＥＭで観察し、粒子断面の総面積に対する空隙の面積割合を測定し、空隙率（空隙面積×１００／粒子断面の総面積）を算出した。空隙率は粒子１０個についての平均値とする。
[Porosity]
1 g of the obtained negative electrode material sample was mixed with polyvinylidene fluoride at a mass ratio of 2: 1, applied to a copper foil, and dried at 105 ° C. The obtained coated foil was subjected to cross-section treatment using an ion milling apparatus (IB19510CP type cross-section polisher) manufactured by JEOL Ltd. to expose the cross-section of the negative electrode material particles. The exposed particle cross section was observed by SEM, the area ratio of the voids to the total area of the particle cross section was measured, and the porosity (void area × 100 / total area of the particle cross section) was calculated. The porosity is an average value for 10 particles.
［初回充電容量及び初回効率］
各実施例及び比較例の負極材試料５質量％に対し、黒鉛系負極材料、スチレンブタジエンゴム（ＳＢＲ）、及び、カルボキシメチルセルロース（ＣＭＣ）を固形分でそれぞれ９７．０質量％、１．５質量％、及び、１．５質量％となるよう加え、混練してペースト状の負極材スラリーを作製した。このスラリーを厚さ１０μｍの電解銅箔に厚さ２００μｍのクオーターを用いて塗布し、さらに、１０５℃で乾燥して水分を除去し、試料電極（負極）を作製した。
[Initial charge capacity and initial efficiency]
97.0% by mass and 1.5% by mass of the graphite-based negative electrode material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in terms of solid content with respect to 5% by mass of the negative electrode material sample of each Example and Comparative Example % And 1.5% by mass were added and kneaded to prepare a paste-like negative electrode material slurry. This slurry was applied to an electrolytic copper foil having a thickness of 10 μm using a quarter having a thickness of 200 μm, and further dried at 105 ° C. to remove water to prepare a sample electrode (negative electrode).
次いで、上記試料電極、セパレータ、対極（正極）の順に積層した後、ＬｉＰＦ６をエチレンカーボネート（ＥＣ）及びメチルエチルカーボネート（ＭＥＣ）（ＥＣとＭＥＣは体積比で３：７）を混合した電解液溶液を注入し、コイン型電池を作製した。対極には金属リチウムを使用し、セパレータには厚み２０μｍのポリエチレン微孔膜を使用した。 Next, after laminating the sample electrode, separator, and counter electrode (positive electrode) in this order, an electrolytic solution in which LiPF 6 is mixed with ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (EC and MEC have a volume ratio of 3: 7). The solution was injected to prepare a coin-type battery. Metallic lithium was used for the counter electrode, and a polyethylene micropore membrane having a thickness of 20 μm was used for the separator.
得られたコイン型電池の試料電極と対極の間に、０．６ｍＡ／ｃｍ２の定電流で０．０６Ｖ（Ｖ ｖｓ． Ｌｉ／Ｌｉ＋）まで充電し、次いで０．６Ｖの定電圧で電流が０．０６ｍＡになるまで充電した。次に３０分の休止時間後に０．６ｍＡ／ｃｍ２の定電流で１．０ Ｖ（Ｖ ｖｓ． Ｌｉ／Ｌｉ＋）まで放電する１サイクル試験を行い、初回充電容量を測定した。さらに、得られた初回充電容量と初回放電容量の差から、初回効率を算出した。 Between the sample electrode and the counter electrode of the obtained coin-type battery, it is charged to 0.06 V (V vs. Li / Li + ) with a constant current of 0.6 mA / cm 2 , and then a current with a constant voltage of 0.6 V. Was charged until the voltage reached 0.06 mA. Next, after a 30-minute rest period, a one-cycle test was conducted in which the battery was discharged to 1.0 V (V vs. Li / Li + ) at a constant current of 0.6 mA / cm 2 , and the initial charge capacity was measured. Furthermore, the initial efficiency was calculated from the difference between the obtained initial charge capacity and the initial discharge capacity.
［サイクル特性］
サイクル特性については、以下のようにして調べた。最初に電池安定化のため２５℃の雰囲気下、２サイクル充放電を行った。この際の条件として、４．２Ｖに達するまで定電流密度、０．５７ｍＡ／ｃｍ２で充電し、４．２Ｖの電圧に達した段階で４．２Ｖ定電圧で電流密度が０．０５７ｍＡ／ｃｍ２に達するまで充電した。また放電時は０．５７ｍＡ／ｃｍ２の定電流密度で電圧が２．７５Ｖに達するまで放電した。その後、３サイクル目から総サイクル数が２０サイクルとなるまで充放電を行い、各サイクルの放電容量を測定した。最後に２０サイクル目の放電容量を３サイクル目の放電容量で割り、％表示のため１００を掛け、容量維持率（以下では単に維持率と呼ぶ場合もある）を算出した。サイクル条件として、４．２Ｖに達するまで定電流密度、０．８６ｍＡ／ｃｍ２で充電し、４．２Ｖの電圧に達した段階で４．２Ｖ定電圧で電流密度が０．０５７ｍＡ／ｃｍ２に達するまで充電した。また放電時は０．８６ｍＡ／ｃｍ２の定電流密度で電圧が２．７５Ｖに達するまで放電した。
[Cycle characteristics]
The cycle characteristics were investigated as follows. First, two cycles of charging and discharging were performed in an atmosphere of 25 ° C. to stabilize the battery. As a condition at this time, the battery is charged at a constant current density of 0.57 mA / cm 2 until it reaches 4.2 V, and when the voltage reaches 4.2 V, the current density is 0.057 mA / cm at a constant voltage of 4.2 V. It was charged until it reached 2 . At the time of discharge, the battery was discharged at a constant current density of 0.57 mA / cm 2 until the voltage reached 2.75 V. After that, charging and discharging were performed from the third cycle until the total number of cycles reached 20 cycles, and the discharge capacity of each cycle was measured. Finally, the discharge capacity at the 20th cycle was divided by the discharge capacity at the 3rd cycle and multiplied by 100 for% display to calculate the capacity retention rate (hereinafter, may be simply referred to as the maintenance rate). As a cycle condition, it is charged at a constant current density of 0.86 mA / cm 2 until it reaches 4.2 V, and when it reaches a voltage of 4.2 V, the current density becomes 0.057 mA / cm 2 at a constant voltage of 4.2 V. Charged until it reached. At the time of discharge, the battery was discharged at a constant current density of 0.86 mA / cm 2 until the voltage reached 2.75 V.
表１中、シリコン粒子の割合とは、原料として用いたシリコン粒子とリチウムシリケート粒子との合計量に対するシリコン粒子の含有率（質量％）を表す。 In Table 1, the ratio of silicon particles represents the content ratio (mass%) of silicon particles with respect to the total amount of silicon particles and lithium silicate particles used as raw materials.
表１からわかるように実施例１〜４の熱処理品であるシリコンとシリケートのコンポジット材は、比較例１の未熱処理品に比べて、良好な放電容量、初回効率及びサイクル特性（放電容量維持率）を有する。また、炭素被覆を行うことにより初回効率及び放電容量がより向上することから、炭素被覆を行うことがより望ましい。 As can be seen from Table 1, the silicon and silicate composite materials, which are the heat-treated products of Examples 1 to 4, have better discharge capacity, initial efficiency, and cycle characteristics (discharge capacity retention rate) than the unheat-treated products of Comparative Example 1. ). Further, it is more desirable to perform carbon coating because the initial efficiency and the discharge capacity are further improved by performing carbon coating.
Claims (17)
A lithium ion secondary battery comprising the negative electrode according to claim 16.
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| WO2022113499A1 (en) * | 2020-11-30 | 2022-06-02 | パナソニックＩｐマネジメント株式会社 | Negative electrode active material for nonaqueous electrolyte secondary batteries, and nonaqueous electrolyte secondary battery |
| WO2022158381A1 (en) * | 2021-01-21 | 2022-07-28 | 三洋電機株式会社 | Negative electrode active material composite particle, method for manufacturing negative electrode active material composite particle, and nonaqueous electrolyte secondary battery |
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| WO2022113499A1 (en) * | 2020-11-30 | 2022-06-02 | パナソニックＩｐマネジメント株式会社 | Negative electrode active material for nonaqueous electrolyte secondary batteries, and nonaqueous electrolyte secondary battery |
| WO2022158381A1 (en) * | 2021-01-21 | 2022-07-28 | 三洋電機株式会社 | Negative electrode active material composite particle, method for manufacturing negative electrode active material composite particle, and nonaqueous electrolyte secondary battery |
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