JP3978881B2

JP3978881B2 - Non-aqueous electrolyte and lithium secondary battery using the same

Info

Publication number: JP3978881B2
Application number: JP23106498A
Authority: JP
Inventors: 俊一浜本; 敦男日高; 幸夫仲田; 浩司安部
Original assignee: Ube Industries Ltd
Current assignee: Ube Corp
Priority date: 1997-08-22
Filing date: 1998-08-18
Publication date: 2007-09-19
Anticipated expiration: 2018-08-18
Also published as: JP2000003724A

Description

【０００１】
本発明は、電池のサイクル特性や、保存特性などの電池特性に優れたリチウム二次電池およびこれに用いる非水電解液に関する。
【０００２】
【従来の技術】
近年、電子機器の小型化、携帯化が進んでおり、それらの駆動電源として、高エネルギ−密度の電池、特に二次電池の開発が求められている。その有力な候補として、正極には、ＬｉＣｏＯ₂、ＬｉＭｎ₂Ｏ₄、ＬｉＮｉＯ₂などのリチウム含有複合酸化物が高い起電力が取り出せるため正極材料として注目され、また負極にはコークス、黒鉛などの炭素材料がデンドライト状の電析リチウムの成長による正極との短絡、負極からのリチウムの脱落がないため、金属リチウム負極を用いたリチウム二次電池に替わる高性能且つ高い安全性を有する負極材料としてますます注目されるようになっている。
【０００３】
【発明が解決しようとする課題】
しかしながら、前記炭素材料を負極に用いた場合には、充放電サイクル数とともに炭素負極上において、電解液として用いられる非水溶媒が分解して電池容量が次第に低下するという問題点があった。このため、電池のサイクル特性および保存特性などの電池特性は必ずしも満足なものではないのが現状である。
【０００４】
特に、正極として前記リチウム含有複合酸化物を用い、負極として天然黒鉛や人造黒鉛などの高結晶化した炭素材料を用いたリチウム二次電池においては、炭素材料の剥離が観察され、現象の程度によっては電気容量やサイクル特性が低下するという問題点があった。この炭素材料の剥離は、電解液中の非水溶媒が充電時に分解することにより起こるのではないかと考えられ、この剥離をもたらす非水溶媒の分解は、炭素材料と電解液との界面における非水溶媒の電気化学的還元に起因するものと考えられている。
【０００５】
例えば、非水溶媒として環状カーボネートが好適に用いられているが、エチレンカーボネート（ＥＣ）のような環状カーボネートを用いたような場合には、充放電を繰り返す間に非水溶媒の分解が起こり、電池性能の低下が起こる。なかでも、融点が低くて誘電率の高いプロピレンカーボネート（ＰＣ）は、低温においても高い電気伝導度を有しているため非水溶媒として好ましいが、高結晶化された黒鉛を負極材料して用いるような場合には、ＰＣの分解が顕著となり、リチウム二次電池用の電解液としては使用できなかった。
【０００６】
本発明は、前記のようなリチウム二次電池用電解液に関する課題を解決し、電池のサイクル特性に優れ、さらに充電状態での保存特性などの電池特性にも優れたリチウム二次電池およびこれに用いる非水電解液を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明は、正極、負極および非水溶媒に電解質が溶解されている非水電解液からなるリチウム二次電池において、正極がリチウム複合酸化物を含む材料であり、負極がグラファイトを含む材料であり、非水溶媒は環状カーボネート（エチレンカーボネートとプロピレンカーボネートとからなる群より選ばれる）および鎖状カーボネートを主成分とし、且つ非水溶媒中に０．１重量％以上４重量％以下の１，３−プロパンスルトンおよび／または１，４−ブタンスルトンが含有されていることを特徴とするリチウム二次電池に関する。
また、本発明は、リチウム複合酸化物を含む材料からなる正極およびグラファイトを含む材料からなる負極を備えたリチウム二次電池用非水電解液において、該非水電解液は非水溶媒に電解質が溶解されている非水電解液であって、非水溶媒は環状カーボネート（エチレンカーボネートとプロピレンカーボネートとからなる群より選ばれる）および鎖状カーボネートを主成分とし、且つ非水溶媒中に０．１〜４重量％の１，３−プロパンスルトンおよび／または１，４−ブタンスルトンが含有されていることを特徴とするリチウム二次電池用非水電解液に関する。
【０００８】
【発明の実施の形態】
本発明における非水溶媒は、主成分として環状カーボネートおよび鎖状カーボネートが含有される。
前記環状カーボネートとしては、エチレンカーボネート（ＥＣ）とプロピレンカーボネート（ＰＣ）からなる群より選ばれる少なくとも一種であることが好ましい。
【０００９】
また、前記鎖状カーボネートとしては、ジメチルカーボネート（ＤＭＣ）、メチルエチルカーボネート（ＭＥＣ）、ジエチルカーボネート（ＤＥＣ）から選ばれる少なくとも一種以上であることが好ましい。
【００１０】
本発明におけるリチウム二次電池用電解液において、前記非水溶媒中の環状カーボネートの含有量が１０重量％以上７０重量％以下であり、前記鎖状カーボネートの含有量が３０重量％以上９０重量％以下であることが好ましく、また、１，３−プロパンスルトンおよび／または１，４−ブタンスルトンの含有量が０．１重量％以上４重量％以下であることが好ましい。
【００１１】
本発明で使用される電解質としては、例えば、ＬｉＰＦ₆、ＬｉＢＦ₄、ＬｉＣｌＯ₄、ＬｉＮ（ＳＯ₂ＣＦ₃）₂、ＬｉＮ（ＳＯ₂Ｃ₂Ｆ₅）₂、ＬｉＣ（ＳＯ₂ＣＦ₃）₃などが挙げられる。これらの電解質は、一種類で使用してもよく、二種類以上組み合わせて使用してもよい。これら電解質は、前記の非水溶媒に通常０．１〜３Ｍ、好ましくは０．５〜１．５Ｍの濃度で溶解されて使用される。
【００１２】
本発明の電解液は、例えば、前記の環状カーボネートおよび鎖状カーボネートを混合し、これに前記の電解質を溶解し、１，３−プロパンスルトンおよび／または１，４−ブタンスルトンを溶解することにより得られる。
【００１３】
二次電池を構成する電解液以外の構成部材については特に限定されず、従来使用されている種々の構成部材を使用できる。
【００１４】
例えば、正極活物質としてはコバルト、マンガン、ニッケル、クロム、鉄およびバナジウムからなる群より選ばれる少なくとも一種類の金属とリチウムとの複合金属酸化物が使用される。このような複合金属酸化物としては、例えば、ＬｉＣｏＯ₂、ＬｉＭｎ₂Ｏ₄、ＬｉＮｉＯ₂などが挙げられる。
【００１５】
正極は、前記の正極活物質をアセチレンブラック、カーボンブラックなどの導電剤、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）などの結着剤および溶剤と混練して正極合剤とした後、この正極材料を集電体としてのアルミニウム箔やステンレス製のラス板に塗布して、乾燥、加圧成型後、５０℃〜２５０℃程度の温度で２時間程度真空下で加熱処理することにより作製される。
【００１６】
負極活物質としては、リチウムを吸蔵・放出可能な黒鉛型結晶構造を有するグラファイトを含む材料、例えば天然黒鉛や人造黒鉛が使用される。特に、格子面（００２）の面間隔（ｄ₀₀₂）が３．３５〜３．４０Å（オングストローム）である黒鉛型結晶構造を有する炭素材料を使用することが好ましい。なお、炭素材料のような粉末材料はエチレンプロピレンジエンターポリマー（ＥＰＤＭ）、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）などの結着剤と混練して負極合剤として使用される。
【００１７】
本発明において、電解液中に含有される１，３−プロパンスルトンおよび／または１，４−ブタンスルトンは、炭素材料表面での不働態皮膜形成に寄与し、天然黒鉛や人造黒鉛などの活性で高結晶化した炭素材料を不働態皮膜で被覆し、電池の正常な反応を損なうことなく電解液の分解を抑制する効果を有するものと考えられる。
【００１８】
リチウム二次電池の構造は特に限定されるものではなく、正極、負極および単層又は複層のセパレータを有するコイン型電池、さらに、正極、負極およびロール状のセパレータを有する円筒型電池や角型電池などが一例として挙げられる。なお、セパレータとしては公知のポリオレフィンの微多孔膜、織布、不織布などが使用される。
【００１９】
【実施例】
次に、実施例および比較例を挙げて、本発明を具体的に説明するが、これらは、本発明を何ら限定するものではない。
【００２０】
実施例１
〔電解液の調製〕
プロピレンカーボネート（ＰＣ）とジメチルカーボネート（ＤＭＣ）とを重量比１：１となるように調製し、さらに１，３−プロパンスルトン（ＰＳ）を０．１重量％となるように加えた。これにＬｉＰＦ₆を１Ｍの濃度になるように溶解して電解液を調製した。
【００２１】
〔リチウム二次電池の作製および電池特性の測定〕
ＬｉＣｏＯ₂（正極活物質）を８０重量％、アセチレンブラック（導電剤）を１０重量％、ポリテトラフルオロエチレン（結着剤）を１０重量％の割合で混合し、これに１−メチル−２−ピロリドン溶剤を加え、混合したものをアルミニウム箔上に塗布し、乾燥、加圧成型、加熱処理して正極を調製した。天然黒鉛（負極活物質）を９０重量％、ポリフッ化ビニリデン（結着剤）を１０重量％の割合で混合し、これに１−メチル−２−ピロリドン溶剤を加え、混合したものを銅箔上に塗布し、乾燥、加圧成型、加熱処理して負極を調製した。この場合、正極と負極の電気容量がほぼ同じになるように調整した。そして、ポリプロピレン微多孔性フィルムのセパレータを用い、上記の電解液を注入させてコイン電池（直径２０ｍｍ、厚さ３．２ｍｍ）を作製した。
このコイン電池を用いて、室温（２５℃）において、０．８ｍＡの定電流及び定電圧で、終止電圧４．２Ｖまで５時間充電し、次に０．８ｍＡの定電流下、終止電圧２．７Ｖまで放電し、この充放電を繰り返した。初回の充電容量は、４１５ｍＡｈ／ｇ炭素、放電容量は３１９ｍＡｈ／ｇ炭素であり、ＥＣ／ＤＭＣ（１／１）を電解液に用いた場合（比較例１）とほぼ同等であり、充放電５０サイクル後の電池特性を測定したところ、初期放電容量を１００％としたときの放電容量維持率は８２．３％であった。その結果を表１に示す。これとは別に、室温（２５℃）において、定電流及び定電圧０．８ｍＡで終止電圧４．２Ｖまで５時間充電した後、−２０℃にして定電流０．８ｍＡで終止電圧２．７Ｖまで放電した。このときの初期放電容量は室温との初期放電容量比で８８％であった。
【００２２】
実施例２〜実施例５
正極活物質、負極活物質および電解液組成を表１記載のようにした以外は実施例１と同様な方法により、コイン電池を作製し、電池特性を測定した。室温下、５０サイクル後の放電容量維持率を表１に示す。
【００２３】
実施例６
正極活物質をＬｉＣｏＯ₂からＬｉＭｎ₂Ｏ₄に代えて、電解液組成を表１記載のようにした以外は実施例１と同様に充放電試験を行った。室温下、５０サイクル後の放電容量維持率を表１に示す。
【００２４】
実施例７
負極活物質を天然黒鉛から人造黒鉛〔大阪ガス化学（株）製ＭＣＭＢ〕に代え、電解液組成を表１記載のようにした以外は実施例１と同様にしてリチウム二次電池を作製して充放電試験を行った。室温下、５０サイクル後の放電容量維持率を表１に示す。
【００２５】
比較例１
電解液組成をＥＣ／ＤＭＣ（重量比１／１）となるようにした以外は実施例１と同様にしてリチウム二次電池を作製して充放電試験を行った。初回の充電容量は、４１１ｍＡｈ／ｇ炭素、放電容量は３２６ｍＡｈ／ｇ炭素であった。室温下、５０サイクル後の放電容量維持率を表２に示す。さらに−２０℃での初期放電容量は室温との初期放電容量比で６２％であった。
【００２６】
比較例２
電解液組成をＰＣ／ＤＭＣ（重量比１／１）となるようにした以外は実施例１と同様にしてリチウム二次電池を作製して充放電試験を行った。しかしながら、この場合には初回充電時に電解液が分解して充電できなかった。結果を表２に示す。
【００２７】
実施例８
１，３−プロパンスルトンの添加量を１重量％とし、非水溶媒をＥＣ−ＤＭＣ（重量比１／２）とした以外は実施例１同様な方法により、コイン電池を作製し、電池特性を測定した。室温下、５０サイクル後の放電容量維持率を表３に示す。
【００２８】
実施例９
１，３−プロパンスルトンの添加量を３重量％とした以外は実施例８と同様な方法により、コイン電池を作製し、電池特性を測定した。室温下、５０サイクル後の放電容量維持率を表３に示す。
【００２９】
実施例１０
１，３−プロパンスルトンに代えて１，４−ブタンスルトンを３重量％添加した以外は実施例８と同様な方法により、コイン電池を作製し、電池特性を測定した。室温下、５０サイクル後の放電容量維持率を表３に示す。
【００３０】
実施例１１
正極活物質としてＬｉＭｎ₂Ｏ₄を使用した以外は実施例９と同様な方法により、コイン電池を作製し、電池特性を測定した。室温下、５０サイクル後の放電容量維持率を表３に示す。
【００３１】
実施例１２
１，３−プロパンスルトンに代えて１，４−ブタンスルトンを３重量％添加した以外は実施例１１と同様な方法により、コイン電池を作製し、電池特性を測定した。室温下、５０サイクル後の放電容量維持率を表３に示す。
なお、本発明は記載の実施例に限定されず、発明の趣旨から容易に置換可能な様々な組み合わせが可能である。特に、上記実施例の溶媒の組み合わせは限定されるものではない。更には、上記実施例はコイン電池に関するものであるが、本発明は円筒型、角型の電池にも適用される。
【００３２】
【発明の効果】
本発明によれば、電池のサイクル特性、保存特性などの電池特性に優れたリチウム二次電池を提供することができる。
【００３３】
【表１】

【００３４】
【表２】

【００３５】
【表３】

[0001]
The present invention relates to a lithium secondary battery excellent in battery characteristics such as battery cycle characteristics and storage characteristics, and a non-aqueous electrolyte used therein.
[0002]
[Prior art]
In recent years, electronic devices are becoming smaller and more portable, and as a driving power source for them, development of a high energy density battery, particularly a secondary battery, is required. As a promising candidate, the positive electrode has attracted attention as a positive electrode material because lithium-containing composite oxides such as LiCoO ₂ , LiMn ₂ O ₄ , and LiNiO ₂ can extract high electromotive force, and the negative electrode has carbon such as coke and graphite. Since the material does not short-circuit with the positive electrode due to the growth of dendritic electrodeposited lithium and does not drop off lithium from the negative electrode, it is a negative electrode material with high performance and high safety that replaces lithium secondary batteries using metallic lithium negative electrodes. It is getting more and more attention.
[0003]
[Problems to be solved by the invention]
However, when the carbon material is used for the negative electrode, there is a problem in that the battery capacity gradually decreases due to decomposition of the nonaqueous solvent used as the electrolytic solution on the carbon negative electrode along with the number of charge / discharge cycles. For this reason, at present, battery characteristics such as battery cycle characteristics and storage characteristics are not always satisfactory.
[0004]
In particular, in a lithium secondary battery using the lithium-containing composite oxide as a positive electrode and a highly crystallized carbon material such as natural graphite or artificial graphite as a negative electrode, peeling of the carbon material is observed, depending on the degree of the phenomenon. However, there is a problem that the electric capacity and cycle characteristics are lowered. This exfoliation of the carbon material may be caused by the decomposition of the non-aqueous solvent in the electrolyte during charging, and the decomposition of the non-aqueous solvent that causes the exfoliation is not caused at the interface between the carbon material and the electrolyte. It is thought to result from the electrochemical reduction of the aqueous solvent.
[0005]
For example, cyclic carbonate is preferably used as the non-aqueous solvent, but when cyclic carbonate such as ethylene carbonate (EC) is used, decomposition of the non-aqueous solvent occurs during repeated charge and discharge, Battery performance is degraded. Among them, propylene carbonate (PC) having a low melting point and a high dielectric constant is preferable as a non-aqueous solvent because it has a high electric conductivity even at a low temperature, but highly crystallized graphite is used as a negative electrode material. In such a case, the decomposition of PC becomes remarkable, and it cannot be used as an electrolyte for a lithium secondary battery.
[0006]
The present invention solves the above-described problems related to the electrolyte for a lithium secondary battery, has excellent battery cycle characteristics, and has excellent battery characteristics such as storage characteristics in a charged state, and to this It aims at providing the nonaqueous electrolyte to be used.
[0007]
[Means for Solving the Problems]
The present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent, wherein the positive electrode is a material containing a lithium composite oxide, and the negative electrode is a material containing graphite. The non-aqueous solvent is composed mainly of cyclic carbonate (selected from the group consisting of ethylene carbonate and propylene carbonate) and chain carbonate, and 0.1 to 4% by weight of 1,3 in the non-aqueous solvent. -It relates to a lithium secondary battery characterized by containing propane sultone and / or 1,4-butane sultone.
The present invention also relates to a non-aqueous electrolyte for a lithium secondary battery provided with a positive electrode made of a material containing a lithium composite oxide and a negative electrode made of a material containing graphite. The non-aqueous electrolyte has an electrolyte dissolved in a non-aqueous solvent. The non-aqueous electrolyte is a non-aqueous solvent comprising a cyclic carbonate (selected from the group consisting of ethylene carbonate and propylene carbonate) and a chain carbonate as main components, and 0.1 to 0.1 in the non-aqueous solvent. The present invention relates to a non-aqueous electrolyte for a lithium secondary battery, wherein 4% by weight of 1,3-propane sultone and / or 1,4-butane sultone is contained.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The non-aqueous solvent in the present invention contains a cyclic carbonate and a chain carbonate as main components.
The cyclic carbonate is preferably at least one selected from the group consisting of ethylene carbonate (EC) and propylene carbonate (PC).
[0009]
The chain carbonate is preferably at least one selected from dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC).
[0010]
In the electrolyte solution for a lithium secondary battery in the present invention, the content of the cyclic carbonate in the non-aqueous solvent is 10% by weight or more and 70% by weight or less, and the content of the chain carbonate is 30% by weight or more and 90% by weight. The content of 1,3-propane sultone and / or 1,4-butane sultone is preferably 0.1 wt% or more and 4 wt% or less.
[0011]
The electrolyte used in the present invention, for _{_{example, LiPF 6, LiBF 4, LiClO}} 4, LiN (SO 2 CF 3) 2, LiN (SO 2 C 2 F 5) 2, LiC (SO 2 CF 3) 3 , etc. Is mentioned. These electrolytes may be used alone or in combination of two or more. These electrolytes are used by being dissolved in the non-aqueous solvent usually at a concentration of 0.1 to 3M, preferably 0.5 to 1.5M.
[0012]
The electrolytic solution of the present invention is obtained, for example, by mixing the cyclic carbonate and the chain carbonate, dissolving the electrolyte, and dissolving 1,3-propane sultone and / or 1,4-butane sultone. It is done.
[0013]
The constituent members other than the electrolytic solution constituting the secondary battery are not particularly limited, and various conventionally used constituent members can be used.
[0014]
For example, a composite metal oxide of at least one metal selected from the group consisting of cobalt, manganese, nickel, chromium, iron, and vanadium and lithium is used as the positive electrode active material. Examples of such a composite metal oxide include LiCoO ₂ , LiMn ₂ O ₄ , and LiNiO ₂ .
[0015]
The positive electrode is obtained by kneading the positive electrode active material with a conductive agent such as acetylene black or carbon black, a binder such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF), and a solvent to form a positive electrode mixture. By applying this positive electrode material to an aluminum foil or stainless steel lath plate as a current collector, and after drying and pressure molding, heat treatment is performed under vacuum at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. Produced.
[0016]
As the negative electrode active material, a material containing graphite having a graphite-type crystal structure capable of inserting and extracting lithium, such as natural graphite and artificial graphite, is used. In particular, it is preferable to use a carbon material having a graphite-type crystal structure in which the lattice spacing ( ₀₀₂ ) (d ₀₀₂ ) is 3.35 to 3.40 Å (angstrom). A powder material such as a carbon material is kneaded with a binder such as ethylene propylene diene terpolymer (EPDM), polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF) and used as a negative electrode mixture.
[0017]
In the present invention, 1,3-propane sultone and / or 1,4-butane sultone contained in the electrolytic solution contributes to the formation of a passive film on the surface of the carbon material, and has high activity such as natural graphite and artificial graphite. It is considered that the crystallized carbon material is coated with a passive film and has an effect of suppressing the decomposition of the electrolyte without impairing the normal reaction of the battery.
[0018]
The structure of the lithium secondary battery is not particularly limited, and a coin-type battery having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, and a cylindrical battery or a square type having a positive electrode, a negative electrode, and a roll separator. An example is a battery. A known polyolefin microporous film, woven fabric, non-woven fabric or the like is used as the separator.
[0019]
【Example】
Next, although an Example and a comparative example are given and this invention is demonstrated concretely, these do not limit this invention at all.
[0020]
Example 1
(Preparation of electrolyte)
Propylene carbonate (PC) and dimethyl carbonate (DMC) were prepared so as to have a weight ratio of 1: 1, and 1,3-propane sultone (PS) was further added so as to be 0.1% by weight. An electrolytic solution was prepared by dissolving LiPF ₆ to a concentration of 1M.
[0021]
[Production of lithium secondary battery and measurement of battery characteristics]
80% by weight of LiCoO ₂ (positive electrode active material), 10% by weight of acetylene black (conductive agent), and 10% by weight of polytetrafluoroethylene (binder) were mixed, and this was mixed with 1-methyl-2- A pyrrolidone solvent was added and the mixture was applied onto an aluminum foil, dried, pressure-molded, and heat treated to prepare a positive electrode. 90% by weight of natural graphite (negative electrode active material) and 10% by weight of polyvinylidene fluoride (binder) are mixed, and a 1-methyl-2-pyrrolidone solvent is added thereto, and the resulting mixture is added to a copper foil. The negative electrode was prepared by drying, pressure molding, and heat treatment. In this case, the positive electrode and the negative electrode were adjusted so that their electric capacities were almost the same. And using the separator of a polypropylene microporous film, said electrolyte solution was inject | poured and the coin battery (diameter 20mm, thickness 3.2mm) was produced.
Using this coin battery, at room temperature (25 ° C.), it was charged at a constant current and constant voltage of 0.8 mA for 5 hours to a final voltage of 4.2 V, and then at a constant current of 0.8 mA and a final voltage of 2. The battery was discharged to 7 V, and this charge / discharge was repeated. The initial charge capacity is 415 mAh / g carbon, the discharge capacity is 319 mAh / g carbon, which is almost the same as when EC / DMC (1/1) is used as the electrolyte (Comparative Example 1), and charge / discharge 50 When the battery characteristics after cycling were measured, the discharge capacity retention rate was 82.3% when the initial discharge capacity was 100%. The results are shown in Table 1. Separately, at room temperature (25 ° C.), after charging for 5 hours to a final voltage of 4.2 V at a constant current and a constant voltage of 0.8 mA, it is set to −20 ° C. to a final voltage of 2.7 V at a constant current of 0.8 mA. Discharged. The initial discharge capacity at this time was 88% in terms of the initial discharge capacity ratio to room temperature.
[0022]
Example 2 to Example 5
A coin battery was produced by the same method as in Example 1 except that the positive electrode active material, the negative electrode active material, and the electrolyte composition were as shown in Table 1, and the battery characteristics were measured. Table 1 shows the discharge capacity retention ratio after 50 cycles at room temperature.
[0023]
Example 6
A charge / discharge test was conducted in the same manner as in Example 1 except that the positive electrode active material was changed from LiCoO ₂ to LiMn ₂ O ₄ and the electrolyte composition was as shown in Table 1. Table 1 shows the discharge capacity retention ratio after 50 cycles at room temperature.
[0024]
Example 7
A lithium secondary battery was prepared in the same manner as in Example 1 except that the negative electrode active material was changed from natural graphite to artificial graphite (MCMB manufactured by Osaka Gas Chemical Co., Ltd.) and the electrolyte composition was as shown in Table 1. A charge / discharge test was conducted. Table 1 shows the discharge capacity retention ratio after 50 cycles at room temperature.
[0025]
Comparative Example 1
A lithium secondary battery was prepared and a charge / discharge test was performed in the same manner as in Example 1 except that the electrolyte composition was EC / DMC (weight ratio 1/1). The initial charge capacity was 411 mAh / g carbon, and the discharge capacity was 326 mAh / g carbon. Table 2 shows the discharge capacity retention ratio after 50 cycles at room temperature. Further, the initial discharge capacity at −20 ° C. was 62% in terms of the initial discharge capacity ratio to room temperature.
[0026]
Comparative Example 2
A lithium secondary battery was produced in the same manner as in Example 1 except that the electrolyte solution composition was PC / DMC (weight ratio 1/1), and a charge / discharge test was performed. However, in this case, the electrolytic solution was decomposed at the time of the first charge and could not be charged. The results are shown in Table 2.
[0027]
Example 8
A coin battery was produced in the same manner as in Example 1 except that the amount of 1,3-propane sultone added was 1% by weight and the non-aqueous solvent was EC-DMC (weight ratio 1/2). It was measured. Table 3 shows the discharge capacity retention rate after 50 cycles at room temperature.
[0028]
Example 9
A coin battery was produced by the same method as in Example 8 except that the amount of 1,3-propane sultone added was 3% by weight, and the battery characteristics were measured. Table 3 shows the discharge capacity retention rate after 50 cycles at room temperature.
[0029]
Example 10
A coin battery was produced in the same manner as in Example 8 except that 3% by weight of 1,4-butane sultone was added instead of 1,3-propane sultone, and the battery characteristics were measured. Table 3 shows the discharge capacity retention rate after 50 cycles at room temperature.
[0030]
Example 11
A coin battery was produced by the same method as in Example 9 except that LiMn ₂ O ₄ was used as the positive electrode active material, and the battery characteristics were measured. Table 3 shows the discharge capacity retention rate after 50 cycles at room temperature.
[0031]
Example 12
A coin battery was produced in the same manner as in Example 11 except that 3% by weight of 1,4-butane sultone was added instead of 1,3-propane sultone, and the battery characteristics were measured. Table 3 shows the discharge capacity retention rate after 50 cycles at room temperature.
In addition, this invention is not limited to the Example described, The various combination which can be substituted easily from the meaning of invention is possible. In particular, the combination of solvents in the above examples is not limited. Furthermore, although the said Example is related with a coin battery, this invention is applied also to a cylindrical type | mold and a square-shaped battery.
[0032]
【The invention's effect】
According to the present invention, a lithium secondary battery excellent in battery characteristics such as battery cycle characteristics and storage characteristics can be provided.
[0033]
[Table 1]

[0034]
[Table 2]

[0035]
[Table 3]

Claims

In a lithium secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent, the positive electrode is a material containing a lithium composite oxide, the negative electrode is a material containing graphite, and a non-aqueous solvent Is composed mainly of a cyclic carbonate and a chain carbonate selected from the group consisting of ethylene carbonate and propylene carbonate , and 0.1 to 4% by weight of 1,3-propane sultone and / or in a non-aqueous solvent. Alternatively, a lithium secondary battery containing 1,4-butane sultone.

The cyclic carbonate content in the non-aqueous solvent is 10% by weight or more and 70% by weight or less, the chain carbonate content is 30% by weight or more and 90% by weight or less, and the 1,3-propane sultone and 2. The lithium secondary battery according to claim 1, wherein the content of 1,4-butane sultone is 0.1 wt% or more and 4 wt% or less.

The lithium secondary battery according to claim 1, wherein the cyclic carbonate is propylene carbonate.

The lithium secondary battery according to claim 1, wherein the chain carbonate is at least one selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

The lithium secondary battery according to claim 1, wherein the graphite is natural graphite or artificial graphite.

2. The lithium secondary battery according to claim 1, wherein a plane interval (d ₀₀₂ ) of a lattice plane (002) of the graphite is 3.35 to 3.40 angstroms (Å).

A non-aqueous electrolyte for a lithium secondary battery having a positive electrode made of a material containing a lithium composite oxide and a negative electrode made of a material containing graphite, wherein the non-aqueous electrolyte is a non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent. The non-aqueous solvent is mainly composed of a cyclic carbonate and a chain carbonate selected from the group consisting of ethylene carbonate and propylene carbonate , and 0.1 to 4% by weight of 1,3 in the non-aqueous solvent. -Propane sultone and / or 1,4-butane sultone is contained, The nonaqueous electrolyte for lithium secondary batteries characterized by the above-mentioned.

The cyclic carbonate content in the non-aqueous solvent is 10% by weight or more and 70% by weight or less, the chain carbonate content is 30% by weight or more and 90% by weight or less, and the 1,3-propane sultone and 8. The nonaqueous electrolytic solution for a lithium secondary battery according to claim 7, wherein the content of 1,4-butane sultone is 0.1 wt% or more and 4 wt% or less.

The non-aqueous electrolyte for a lithium secondary battery according to claim 7, wherein the cyclic carbonate is propylene carbonate.

The non-aqueous electrolyte for a lithium secondary battery according to claim 7, wherein the chain carbonate is at least one selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

The non-aqueous electrolyte for a lithium secondary battery according to claim 7, wherein the graphite is natural graphite or artificial graphite.

The nonaqueous electrolytic solution for a lithium secondary battery according to claim 7, wherein a plane interval (d ₀₀₂ ) of a lattice plane (002) of the graphite is 3.35 to 3.40 angstroms (Å).