JP6057208B2 - Electroplating solution, method for producing active material for lithium secondary battery, and lithium secondary battery - Google Patents

Description

  The present invention is produced using an electroplating solution for producing an active material for lithium secondary battery containing silicon, a method for producing an active material for lithium secondary battery using the electroplating solution, and the active material. The present invention relates to a lithium secondary battery including a negative electrode.

A lithium secondary battery is used as a power source for portable electronic devices and the like. In a general lithium secondary battery, a carbon material typified by graphite is used as the negative electrode active material. However, in the active material made of graphite, lithium can be inserted only up to the composition of LiC ₆ and the theoretical energy capacity is 372 mAh / g.

  When silicon is used as the active material, the theoretical energy capacity per negative electrode active material is 4200 mAh / g, and a large-capacity lithium battery can be realized.

  However, a negative electrode using silicon as an active material is accompanied by a large volume change when charging and discharging. For this reason, there is a problem that the active material is dropped and the capacity is reduced when charging and discharging are repeated. For this reason, studies have been made on alloying the active material with a third metal, compositing with a carbon material, making the film thin, making it porous, and roughening the current collector.

  In Japanese Patent Laid-Open Nos. 2012-89267 and 2012-204195, the inventors have uniformly dispersed silicon, oxygen, and carbon, and the composition ratio of silicon to oxygen is SiOx (0.1 ≦ X It is <2), and it is disclosed that a battery having a small capacity change due to charge / discharge can be provided by using an amorphous and metastable phase Si—O—C active material. This active material is manufactured from an electrolytic solution containing silicon ions, oxygen, and carbon by an electrochemical film formation method.

  However, it has been required to more stably produce a lithium secondary battery having better charge / discharge cycle characteristics.

JP-A-2005-116264 discloses a method for producing a negative electrode of a lithium secondary battery by electrodepositing silicon on a ribbon. However, the specification states that care is taken to prevent the deposited Si from being oxidized and converted to SiO or SiO ₂ . That is, the invention for electrodepositing oxidized silicon is positively excluded.

JP 2012-89267 A JP 2012-204195 A JP-A-2005-116264

  The present invention provides an electroplating solution capable of stably producing an active material for a lithium secondary battery exhibiting good charge / discharge cycle characteristics, and an active material for a lithium secondary battery capable of stably producing the active material for a lithium secondary battery. And a lithium secondary battery including a negative electrode manufactured using the active material.

The electroplating solution of the embodiment contains silicon, oxygen, and 10 to 70 at% carbon, the composition ratio of silicon and oxygen is SiOx (0.1 ≦ X <2.0), and is an amorphous and metastable phase. An electroplating solution for electrodepositing an active material for lithium secondary battery comprising Si—O—C, comprising silicon ions, electrolyte ions, nonaqueous solvent, and 0.001 to 10 vol% of fluoroethylene carbonate And one or more carbonate-based additives selected from vinylene carbonate and dipropyl carbonate .

In another embodiment, the method for producing an active material for a lithium secondary battery includes silicon, oxygen, and 10 to 70 at% carbon, and the composition ratio of silicon to oxygen is SiOx (0.1 ≦ X <2 0.0), an amorphous and metastable phase Si—O—C active material production method for a lithium secondary battery, comprising silicon ions, electrolyte ions, non-aqueous solvent, Electrodeposition is performed using an electroplating solution containing 10 vol% of one or more carbonate-based additives selected from fluoroethylene carbonate, vinylene carbonate, and dipropyl carbonate .

Moreover, the lithium secondary battery of another embodiment is 1 type chosen from a silicon ion, electrolyte ion, a nonaqueous solvent, 0.001-10 vol% of fluoroethylene carbonate, vinylene carbonate, and dipropyl carbonate. It contains silicon, oxygen, and 10 to 70 at% carbon produced by electrodeposition using an electroplating solution containing the above carbonate-based additive, and the composition ratio of silicon and oxygen is SiOx ( 0.1 ≦ X <2.0), and a negative electrode manufactured using an active material for a lithium secondary battery made of amorphous and metastable Si—O—C.

  ADVANTAGE OF THE INVENTION According to this invention, the electroplating liquid which can manufacture stably the active material for lithium secondary batteries which shows favorable charging / discharging cycling characteristics, The lithium secondary battery which can manufacture the said active material for lithium secondary batteries stably A method for producing an active material and a lithium secondary battery including a negative electrode produced using the active material can be provided.

It is sectional drawing for demonstrating the structure of a lithium battery. It is a schematic diagram for demonstrating the manufacturing apparatus of the active material for lithium secondary batteries of embodiment. It is a charging / discharging cycle characteristic evaluation result of the battery using the active material for lithium secondary batteries of embodiment.

  Hereinafter, the manufacturing method of the electroplating liquid 30 and the active material for lithium secondary batteries of embodiment of this invention is demonstrated. The electroplating solution 30 contains silicon, oxygen, and 10 to 70 at% carbon, the composition ratio of silicon and oxygen is SiOx (0.1 ≦ X <2.0), and is amorphous and metastable. The active material for lithium secondary batteries which is a phase can be electrodeposited. “˜” indicates “above and below”.

  The inventors have further diligently studied the inventions disclosed in JP 2012-89267 A and JP 2012-204195 A and have invented the electroplating solution 30 and the like.

<Configuration example of lithium secondary battery>
As shown in FIG. 1, the lithium battery 10 is, for example, disposed between a negative electrode 13 having an active material 12 formed on a current collector 11, a positive electrode 14, and the negative electrode 13 and the positive electrode 14. 17, a separator 15 that forms 17, an electrolytic solution 16 that fills the storage region 17, and a sealing structure 18. That is, the basic components of the lithium battery 10 are the negative electrode 13, the positive electrode 14, and the electrolytic solution 16.

<Manufacture of negative electrode (active material) for lithium secondary battery>
As shown in FIG. 2, the active material 12 of the embodiment is manufactured by performing electrodeposition using an electroplating solution 30. For example, the electrodeposition apparatus 20 uses the platinum wire 23 as an anode and the copper foil 22 as a cathode. The copper foil 22 is the current collector 11 and becomes a part of the negative electrode 13.

Li / Li ⁺ (TBAClO ₄ ) was used as the reference electrode 21. That is, in the following description, the potential V is represented by (vs. Li / Li ⁺ ). TBA is an abbreviation for Tetra Butyl Ammonium.

The electroplating solution 30 contains silicon ions, electrolyte ions, 0.001 to 10 vol% carbonate-based additive, and a non-aqueous solvent. For example, the electroplating solution 30 includes 0.5 M / liter SiCl ₄ , 0.5 M / liter TBAClO ₄ , 1 vol (volume)% fluoroethylene carbonate (FEC), propylene carbonate (PC), or the like. Become. SiCl ₄ is a silicon ion source, TBAClO ₄ is an electrolyte ion source, FEC is a carbonate-based additive, and PC is a non-aqueous solvent.

  That is, as the non-aqueous solvent, not only dimethoxyethane (DME), diethoxyethane (DEE), acetonitrile, propylnitrile, ethyl ether, dimethyl sulfoxide, or methylpyrrolidone but also carbonates such as PC or ethylene carbonate (EC) System solvents can also be used.

  A carbonate-based solvent and a carbonate-based additive are similar, but there is a difference in adsorption ability to the cathode surface. That is, the carbonate-based solvent also has a “—O— (C═O) —” structure like the carbonate-based additive, but is composed of C, H, and O, and is nucleophilic and electrophilic. Is relatively small. On the other hand, the carbonate-based additive has nucleophilicity and electrophilicity due to polarization by a polar atom such as F or double bond.

  The carbonate solvent is also adsorbed on the cathode surface and contributes to the eutectoid of O and C into the film. That is, an active material produced from an electroplating solution without adding a carbonate-based additive may also be made of Si—O—C, but an active material having a desired composition and structure may not be obtained.

  On the other hand, an active material having a desired composition and structure can be stably produced by using the electroplating solution 30 to which a carbonate-based additive is added.

  As the carbonate solvent, for example, one or more selected from PC, EC, butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and the like can be used.

  As a carbonate type additive, 1 or more types chosen from FEC, vinylene carbonate (VC), dipropyl carbonate, etc. can be used, for example.

  And, as will be described later, an electroplating solution using a carbonate solvent as a nonaqueous solvent and further adding a carbonate additive is preferable, and particularly preferably, PC is used as a nonaqueous solvent and FEC is used as a carbonate additive. The electroplating solution 30 of the embodiment used is particularly preferred.

Controls at a current density I = 1.0mA / cm ² to 2C (coulomb) / cm ² of current electrical quantity, the active material 12 as a current collector 11, negative electrode was deposited on a 80μm copper foil 22 13 was produced.

<Analysis of active materials for lithium secondary batteries>
When an in-plane distribution (mapping) of elements constituting the active material 12 was measured using an energy dispersive X-ray fluorescence analyzer (EDX), Si, O, and C were uniformly dispersed.

  Next, when X-ray diffraction (XRD) analysis was performed, peaks corresponding to Si (111), Si (220), Si (311), and Si (400) were not confirmed. That is, the active material 12 was amorphous (amorphous). Conversely, in the present invention, amorphous means a state in which no peak is confirmed in a normal XRD analysis.

Next, the active material 12 was analyzed by X-ray photoelectron spectroscopy (XPS). The binding energy of Si 2p _3/2 of the active material 12 was not 99.5 eV indicating Si or 103.5 eV indicating SiO ₂ , but 101 eV to 103 eV therebetween.

The Si oxide having Si 2p _3/2 binding energy of 101 eV to 103 eV is SiO. SiO is not a stable phase like SiO ₂ but a metastable phase in a non-equilibrium state. For this reason, although the structure of SiO etc. is unknown, it turned out that Si contained in the active material 12 is a metastable phase.

  The metastable phase is a phase that does not exist in a thermal equilibrium state, and is a thermodynamically unstable phase that may exist temporarily if some condition is satisfied.

  Next, a composition analysis result of the active material 12 by glow discharge emission spectroscopic analysis (GDOES) is shown below. In addition, the following is a value at a place having a depth of 1 μm from the surface of the active material 12 with less surface contamination and the influence of the current collector 11.

Si: 44 at%
O: 21 at%
C: 35at%

  As shown by the above XPS and GDOES analysis results, the Si silicon and oxygen of the active material 12 were in the state of SiOx (X = 0.48). More strictly, the active material 12 contains a large amount of carbon and thus is in a “Si—O—C” state.

  Carbon in the active material 12 contributes to making the active material 12 amorphous and metastable.

  That is, the active material 12 is not a bulk mixture such as active material powder + conducting aid + binder, core shell structure, or μm order level matrix structure, but a metastable phase having a matrix structure at the atomic level or nm order level. Amorphous.

<Characteristic evaluation of lithium secondary battery>
Next, characteristic evaluation of the lithium battery 10 will be described.

For the evaluation of the characteristics of the secondary battery, the same tripolar cell as the electrodeposition apparatus 20 was used. The working electrode is the negative electrode 13, the counter electrode is Li foil, the reference electrode is Li / Li ⁺ (TBAClO ₄ ), and the electrolytic solution is 1 M LiClO ₄ / EC: PC (1: 1 vol%). It was.

In cyclic voltammetry (CV) measurement, the lower limit potential was 0.01 V, the upper limit potential was 1.2 V from the open circuit potential, and the sweep rate was 0.1 mV. The constant current charge / discharge test (cycle test) was performed in a potential range of 50 μA / cm ² and 0.01 V to 1.2 V.

  In the first charge / discharge cycle, the SiOx (X ≦ 2.0) silicon of the active material 12 is reacted with lithium to become the active material 12A. The active material 12A contains silicon, oxygen, carbon, and lithium, and lithium is in an oxidized state. The active material 12A is produced by reacting silicon of the active material 12 produced from the electroplating solution 30 by electroplating with lithium to form an alloy. That is, the first charge / discharge cycle can be regarded as a manufacturing process.

  As shown in FIG. 3, the Coulomb efficiency of the lithium battery 10 having the active material 12 was 99% after 50 cycles. On the other hand, the Coulomb efficiency of the lithium battery having the active material manufactured using the FEC non-added bath in which no FEC was added to the electroplating bath 30 was less than 98%.

When the active material 12A, that is, the active material 12A having Si (—C) and Li ₂ O (—C) is used, no further irreversible component is generated after the battery is manufactured. For this reason, it is considered that the capacity does not decrease.

  Furthermore, when the trial production and the charge / discharge cycle test were performed while changing the composition, current density and the like of the electroplating solution 30, the following results were obtained. A plurality of trials were made, and a determination was made based on the fact that a lithium secondary battery exhibiting good charge / discharge cycle characteristics can be stably manufactured.

  The addition amount of the carbonate-based additive provided a certain effect in the range of 0.001 to 10 vol%, and particularly preferably in the range of 0.1 to 5 wt%. The electroplating solution 30 containing PC as a non-aqueous solvent and FCE as a carbonate-based additive showed the best characteristics.

  Further, when the carbon content of the active material 12 was in the range of 10 to 70 at% and the composition ratio of silicon and oxygen was in the range of SiOx (0.1 ≦ X <20), a certain effect was obtained. The active material 12 having the above composition was amorphous and metastable.

  The present invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Lithium battery 11 ... Current collector 12 ... Active material 13 ... Negative electrode 14 ... Positive electrode 15 ... Separator 16 ... Electrolytic solution 17 ... Storage area 18 ... Sealing structure 20 ... Electrodeposition apparatus 21 ... Reference electrode 22 ... Copper foil 23 ... Platinum wire 30 ... Plating solution

Claims (7)

It contains silicon, oxygen, and 10 to 70 at% carbon, the composition ratio of silicon and oxygen is SiOx (0.1 ≦ X <2.0), and is made of amorphous and metastable Si—O—C. An electroplating solution for electrodepositing an active material for a lithium secondary battery,
It includes silicon ions, electrolyte ions, nonaqueous solvents, and 0.001 to 10 vol% of one or more carbonate-based additives selected from fluoroethylene carbonate, vinylene carbonate, and dipropyl carbonate. An electroplating solution .   The electroplating solution according to claim 1, wherein the non-aqueous solvent is a carbonate-based solvent. The carbonate solvent is propylene carbonate,
The electroplating solution according to claim 2, wherein the carbonate-based additive is fluoroethylene carbonate. It contains silicon, oxygen, and 10 to 70 at% carbon, the composition ratio of silicon and oxygen is SiOx (0.1 ≦ X <2.0), and is made of amorphous and metastable Si—O—C. A method for producing an active material for a lithium secondary battery, comprising:
An electroplating solution comprising silicon ions, electrolyte ions, a non-aqueous solvent, and 0.001 to 10 vol% of at least one carbonate-based additive selected from fluoroethylene carbonate, vinylene carbonate, and dipropyl carbonate A method for producing an active material for a lithium secondary battery, wherein electrodeposition is performed using   The method for producing an active material for a lithium secondary battery according to claim 4, wherein the non-aqueous solvent is a carbonate-based solvent. The carbonate solvent is propylene carbonate,
The said carbonate type additive is a fluoroethylene carbonate, The manufacturing method of the active material for lithium secondary batteries of Claim 5 characterized by the above-mentioned. An electroplating solution comprising silicon ions, electrolyte ions, a non-aqueous solvent, and 0.001 to 10 vol% of at least one carbonate-based additive selected from fluoroethylene carbonate, vinylene carbonate, and dipropyl carbonate Containing silicon, oxygen, and 10 to 70 at% carbon, and the composition ratio of silicon and oxygen is SiOx (0.1 ≦ X <2.0), A lithium secondary battery comprising a negative electrode manufactured using an active material for a lithium secondary battery comprising amorphous and metastable phase Si—O—C.

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