JP4617702B2 - Lithium secondary battery and manufacturing method thereof - Google Patents

Description

  The present invention relates to a method for manufacturing a lithium secondary battery, and more particularly, to a method for manufacturing a lithium secondary battery including a negative electrode having a carbon material. Moreover, this invention relates to the lithium ion secondary battery manufactured by this method.

A lithium secondary battery (lithium ion secondary battery) is known that has a positive electrode and a negative electrode having a material (active material) capable of occluding and releasing lithium ions, and that is charged and discharged by the movement of lithium ions between the electrodes. It has been. As the negative electrode active material (negative electrode active material), a carbon material capable of inserting and extracting lithium ions can be used. In a typical embodiment of a battery using such a negative electrode active material, lithium ions are inserted between carbon material layers by charging, and lithium ions are desorbed from the interlayer during discharge. In Patent Document 1, after inserting a cation or an anion into a carbon material, the insert is removed by heat treatment, and thus the charge / discharge capacity of a non-aqueous secondary battery is obtained by using a carbon material having an increased interlayer distance. Techniques for improving the performance are described. Patent Documents 2 and 3 describe techniques for obtaining a carbon material suitable as a negative electrode material or the like for a lithium secondary battery by performing various treatments on a carbon material such as graphite.
JP-A-5-82130 Japanese Patent Laid-Open No. 2002-8653 Japanese Patent Laid-Open No. 9-249407

However, according to the method of sequentially performing the process for improving the battery characteristics on the carbon material in advance and the process for constructing the battery using the processed carbon material, the production efficiency of the lithium secondary battery is reduced. It tends to be.
Accordingly, an object of the present invention is to provide a method for efficiently producing a lithium secondary battery including a negative electrode having a carbon material and having improved battery performance (for example, output characteristics). To do. Another object of the present invention is to provide a lithium secondary battery manufactured by such a method.

  In general, in the manufacture of a lithium secondary battery, the present inventor, after assembling battery components such as an electrode and an electrolyte, for the purpose of stabilizing battery performance, We focused on the point to do. And it discovered that the said subject could be solved by performing the process for battery performance improvement to the carbon material which comprises the negative electrode of the said assembly using this conditioning process, and completed this invention.

A method for producing a lithium secondary battery provided by the present invention includes a positive electrode having a material capable of inserting and extracting lithium ions, a negative electrode having a carbon material capable of inserting and extracting lithium ions, and an ion radius greater than that of lithium ions. And an initial electrolyte containing a large cation. And the process which performs initial charge to this battery assembly is included.
According to this method, the cation contained in the initial electrolytic solution can be inserted into the carbon material of the negative electrode by the initial charging (referring to charging the battery assembly for the first time). By inserting this cation (having a larger ionic radius than lithium ions), the interlayer distance of the carbon material can be increased. Thereby, battery performance can be improved. The said initial charging process can be performed as a part of conditioning (initial charging / discharging) process currently performed with the conventional general lithium secondary battery manufacturing method, for example. Therefore, according to the method of the present invention, a battery with better performance (for example, output characteristics) can be manufactured without excessively complicating the manufacturing process of the lithium secondary battery.

Here the initial electrolyte used in the methods disclosed is the initial electrolyte containing one or two cations selected from the group consisting of alkali metal ions other than lithium. It is particularly preferable to use an initial electrolytic solution containing sodium ions (Na ⁺ ), potassium ions (K ⁺ ), or both.

In a preferred embodiment, an initial electrolytic solution containing a non-aqueous solvent, and a salt of the cation and a lithium salt (supporting salt) dissolved in the solvent is used. An initial electrolyte solution in which the anions constituting these salts are common is more preferable. The initial electrolytic solution contains a cation (for example, Na ⁺ and / or K ⁺ ) having a larger ionic radius than lithium ion (Li ⁺ ) at a concentration of 0.002 to 0.3 mol / liter (mol / L). contains. By using such an initial electrolytic solution, the application effect of the present invention can be better exhibited.

The initial charge is preferably performed at a charge rate of 1/3 C or less until at least 20% SOC (State of Charge) is reached. Moreover, it is preferable to carry out at a charge rate of 1/3 C or less until at least the cation concentration of the initial electrolytic solution is reduced to 0.03 mol / liter or less. By starting the initial charging at such a relatively low charging rate, the cations contained in the initial electrolyte can be more appropriately inserted into the carbon material. Thereby, a battery with better battery performance can be manufactured efficiently.
Furthermore, according to this invention, the lithium secondary battery manufactured by one of the methods mentioned above is provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail. It should be noted that technical matters other than the contents particularly mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters for those skilled in the art based on the prior art. The present invention can be carried out based on the technical contents disclosed in the present specification and the common general technical knowledge in the field.

The method of the present invention can be applied to the production of various lithium secondary batteries (typically lithium ion secondary batteries) including a negative electrode having a carbon material capable of inserting and removing Li ⁺ .
As said carbon material, what contains a graphite structure (layered structure) at least in part can be used. Any carbon material such as so-called graphite (graphite), non-graphitizable carbon (hard carbon), easily graphitized carbon (soft carbon), or a combination of these is used. Is possible. For example, natural graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), etc. can be used as the graphite. Usually, it is preferable to use a carbon material mainly composed of carbon having relatively high crystallinity. A carbon material having a structure in which the surface of carbon having relatively high crystallinity is covered with amorphous carbon can be preferably used. When such a carbon material is used, an effect (for example, an effect of improving battery performance) by applying the present invention can be exhibited particularly well.

  The method of the present invention can be carried out using a negative electrode having such a carbon material as a negative electrode active material. For example, it is preferable to use a negative electrode in which the carbon material is attached to a conductive member together with a binder (binder) or the like as necessary. As such a conductive member (negative electrode current collector), a rod-like body, a plate-like body, a foil-like body or the like mainly composed of aluminum, nickel, titanium or the like can be used. Alternatively, carbon paper or the like may be used as the negative electrode current collector. Examples of the binder include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), styrene butadiene block copolymer (SBR), carboxymethyl cellulose ( CMC) or the like can be used. Although it does not specifically limit, the usage-amount of the binder with respect to 100 mass parts of negative electrode active materials (carbon material) can be made into the range of about 0.5-10 mass parts, for example. In addition, it is also possible to use the negative electrode which shape | molded the said carbon material in predetermined shape (for example, pellet shape) with the above binders etc. as needed.

The positive electrode used in the present invention comprises a material that can occlude and release Li ⁺ . A material in which such a material (positive electrode active material) is attached to a conductive member can be used. As the conductive member (positive electrode current collector), a rod-like body, a plate-like body, a foil-like body or the like mainly composed of aluminum, nickel, titanium, or the like can be used. Alternatively, carbon paper or the like may be used as the positive electrode current collector. As the positive electrode active material, an oxide-based positive electrode active material having a layered structure, an oxide-based positive electrode active material having a spinel structure, and the like used for a general lithium secondary battery can be preferably used. For example, the main component is lithium cobalt complex oxide (typically LiCoO ₂ ), lithium nickel complex oxide (typically LiNiO ₂ ), lithium manganese complex oxide (LiMn ₂ O ₄ ), or the like. A positive electrode active material can be used. Such a positive electrode active material can be made into a positive electrode in a form in which it is attached to a positive electrode current collector together with a conductive material, a binder (binder), and the like as necessary. As the conductive material, carbon powder such as carbon black (acetylene black or the like), conductive metal powder such as nickel powder, or the like can be used. As the binder, the same as the negative electrode can be used. Although it does not specifically limit, the usage-amount of the electrically conductive material with respect to 100 mass parts of positive electrode active materials can be made into the range of 1-15 mass parts, for example. Moreover, the usage-amount of the binder with respect to 100 mass parts of positive electrode active materials can be made into the range of about 1-10 mass parts, for example.

The initial electrolytic solution constituting the battery assembly contains a cation having an ionic radius larger than that of Li ⁺ . Here, the magnitude of the ionic radius between Li ⁺ and other cations can be grasped, for example, by comparing the values of the ionic radii described in the Chemical Handbook (edited by the Chemical Society of Japan). Examples of cations having a larger ion radius than Li ⁺ include alkali metal ions such as sodium ion (Na ⁺ ), potassium ion (K ⁺ ), rubidium ion (Rb ⁺ ), cesium ion (Cs ⁺ ); magnesium ion ( Mg ²⁺ ), calcium ions (Ca ²⁺ ), strontium ions (Sr ²⁺ ), barium ions (Ba ²⁺ ) and other alkaline earth metal ions (including Mg); iron (II) ions (Fe ²⁺ ), manganese ( II) Transition metal ions such as ions (Mn ²⁺ ) and the like. Further, the cation contained in the initial electrolytic solution is not limited to such a monoatomic ion, and may be a cation (cation atomic group) containing a plurality of atoms. These may contain only one kind of cation having a larger ion radius than Li +, or may contain two or more kinds.

Among these, preferable cations include one or more selected from the group consisting of alkali metal ions and alkaline earth metal ions. It is more preferable to use an initial electrolytic solution containing one or more cations selected from the group consisting of alkali metal ions. Further, it is preferable to use an initial electrolytic solution containing a cation having an ionic radius of about 1.2 to 2 times the ionic radius of Li ⁺ . Particularly preferred initial electrolytes include those containing Na ⁺ , those containing K ⁺ , those containing Na ⁺ and K ⁺ , and the like.

  In a typical embodiment of the method disclosed herein, the initial electrolytic solution includes a non-aqueous solvent, a lithium salt (supporting salt) dissolved in the solvent, and a salt of the cation. As the non-aqueous solvent, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be used. For example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate, ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyl Tetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone, etc. One kind or two or more kinds selected from non-aqueous solvents known to be usable for an electrolyte solution of a secondary battery or the like) can be used.

The supporting salt contained in the initial electrolyte includes LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO _{2 3} ) One or two or more lithium compounds (lithium salts) selected from Li, LiI, and the like can be used.
Moreover, as the salt of the cation, a salt that can be ionized in the initial electrolytic solution to generate a cation having an ionic radius larger than that of Li ⁺ can be appropriately selected. For example, anions such as BF ₄ ⁻ , PF ₆ ⁻ , ClO ₄ ⁻ , AsF ₆ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ and the above One kind or two or more kinds selected from salts with cations can be used. It is preferable to use a salt of an anion of the same type as the anion constituting the lithium salt (supporting salt) and the cation (preferably an alkali metal).

In a preferred embodiment of the present invention, a cation having an ionic radius larger than that of Li ⁺ is 0.002 to 1 mol / L (more preferably 0.005 to 0.5 mol / L, and still more preferably 0.01 to 0.3 mol / L). ) Is used. Such an initial electrolytic solution can be prepared, for example, by adding and mixing (dissolving) a predetermined amount of the cation salt in a non-aqueous solvent. In an initial electrolytic solution containing a plurality of types of cations having a larger ionic radius than Li ⁺ , the total concentration thereof is preferably in the above range. If the concentration of the cation having a larger ionic radius than Li ⁺ is too low, the application effect of the present invention (for example, the effect of reducing the reaction resistance) may be reduced. On the other hand, even if the concentration of the cation is increased to a certain level, the effect obtained thereby tends to be almost saturated. According to the initial electrolytic solution containing a cation having a larger ionic radius than Li ⁺ at the above concentration, the application effect of the present invention can be exhibited efficiently.

The concentration of the lithium compound (supporting salt) contained in the initial electrolytic solution is not particularly limited. For example, an initial electrolytic solution containing the lithium compound at a concentration of 0.1 to 5 mol / L (preferably 0.2 to 3 mol / L, more preferably 0.5 to 2 mol / L) can be used. An initial electrolytic solution containing Li ⁺ at a higher concentration than the cation concentration (for example, an initial electrolytic solution containing a supporting salt at a higher concentration than the cation salt) is preferable. The relationship between the concentration of Li ⁺ in the initial electrolyte and the concentration of the cation (or the molar ratio of the supporting salt contained in the initial electrolyte and the salt of the cation) is 50% or less of the cation with respect to Li ⁺ . It is preferably in the range of (typically 0.1 to 50%), more preferably in the range of 30% or less (typically 0.1 to 30%).
Note that by performing initial charging on the battery assembly, at least a part of the cations (that is, cations having an ion radius larger than Li ⁺ ) are inserted into the carbon material. And at least one part of the inserted cation can be hold | maintained in a carbon material also by subsequent discharge. Therefore, the electrolytic solution constituting the lithium secondary battery finally obtained through the above initial charging (typically through a plurality of charging / discharging including the initial charging) is the initial electrolytic solution constituting the battery assembly. The concentration of the cation and the concentration ratio between the cation and Li ⁺ can be different from the (electrolytic solution before initial charge).

  The step of obtaining the battery assembly can be performed as follows, for example. That is, a positive electrode sheet in which a positive electrode active material is attached to one side or both sides of a sheet-like positive electrode current collector is prepared. This positive electrode sheet is prepared by, for example, preparing a positive electrode composition by mixing a positive electrode active material, a conductive material and a binder used as necessary, with an appropriate liquid medium, and then collecting the composition into a positive electrode current collector. It can be produced by attaching (for example, coating) one or both sides of the body. In addition, a negative electrode sheet is prepared in which a negative electrode active material (mainly the carbon material) is attached to one or both surfaces of a sheet-like negative electrode current collector. This negative electrode sheet can be produced by the same method as the positive electrode sheet. Then, the positive electrode sheet and the negative electrode sheet are overlapped (stacked) via a separator. As the separator, for example, a porous film made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP) can be used. Moreover, you may use the woven fabric or nonwoven fabric which consists of a polypropylene, a polyethylene terephthalate (PET), methylcellulose, etc. This laminate is housed in a suitable battery container. In a preferred embodiment, the laminate is wound to form a wound electrode body, which is accommodated in a battery container. Alternatively, a stacked electrode body in which a plurality of positive electrode sheets and a plurality of negative electrode sheets are alternately stacked with separators interposed therebetween may be housed in a battery container.

On the other hand, an initial electrolytic solution containing Li ⁺ and the cation (that is, a cation having a larger ion radius than Li ⁺ ) is prepared. Preferably, an initial non-aqueous solvent, a lithium salt, and a salt of the cation are mixed at a predetermined ratio to prepare an initial electrolytic solution containing Li ⁺ and the cation at a predetermined concentration. Then, an initial electrolytic solution is supplied (injected) into the battery container containing the positive electrode and the negative electrode. Thereby, the positive electrode, the negative electrode, and the separator are impregnated with the initial electrolytic solution. In this way, a battery assembly can be obtained.

The step of initially charging the battery assembly can be performed in the same manner as the operation for conditioning (initial charge / discharge) in a conventional general lithium battery manufacturing method. Typically, charging is performed by connecting an external power source between a positive electrode and a negative electrode constituting the battery assembly. At this time, when performing the first charge (initial charge), a charge rate of 1/3 C or less (typically 1/20 C to 1/3 C) from the start of charge to at least SOC 20%. (Current value) is preferable. It is more preferable to carry out at a charging rate (current value) of 1 / 5C or less (typically 1 / 20C to 1 / 5C). By performing the initial charge under such conditions, the cation contained in the initial electrolyte can be more appropriately inserted into the carbon material. Therefore, the interlayer distance of the carbon material can be efficiently increased. Here, “1C” refers to a current value at which the battery is fully charged (SOC 100%) in one hour.
In addition, when performing the initial charge, 1/3 C or less (typical) from the start of charge until a predetermined amount of the cation (that is, a cation having an ionic radius larger than Li ⁺ ) is inserted into the carbon material. Is preferably performed at a charging rate (current value) of 1/20 C to 1/3 C), and at a charging rate (current value) of 1/5 C or less (typically 1/20 C to 1/5 C). More preferably. For example, when the concentration of the cation (Na ⁺ , K ⁺ etc.) contained in the initial electrolytic solution is about 0.04 to 0.1 mol / L, at least the cation remaining in the electrolytic solution from the start of charging. Until the concentration decreases to about 0.03 mol / L or less (typically about 0.02 to 0.03 mol / L), it is preferable to charge at the above-described charging rate. By performing the initial charge under such conditions, the cation contained in the initial electrolyte can be more appropriately inserted into the carbon material.

  Usually, it is preferable to discharge the battery assembly that has been initially charged, and to perform charging and discharging. Typically, 1 to 5 (for example, 2 to 3) charge / discharge cycles including the initial charge are performed. Thereby, effects such as stabilization of battery performance can be obtained. In the second and subsequent charging, the charging rate up to SOC 20% (or the charging rate until the cation concentration of the electrolytic solution decreases to a predetermined value) may be the same as the initial charging. May be performed at different charge rates (eg, higher charge rates). From the viewpoint of improving manufacturing efficiency, it is preferable to set a charging rate (particularly a charging rate up to SOC 20%) in the second and subsequent charging higher than that in the initial charging.

According to any one of the lithium secondary battery manufacturing methods described above, by performing initial charging on the battery assembly, the cation (that is, a cation having a larger ion radius than Li ⁺ ) contained in the initial electrolyte of the assembly. Can be inserted into the carbon material constituting the negative electrode of the assembly. As a result, the interlayer distance of the carbon material can be increased, and the energy required for insertion and removal of Li ⁺ can be reduced. Such a decrease in energy can effectively contribute to an improvement in battery performance (for example, at least one kind of performance among output characteristics, charge / discharge capacity, cycle characteristics, etc.). Note that the decrease in energy required for insertion / extraction of Li ⁺ can be grasped as a decrease in the reaction resistance value of the battery, for example.
According to the method disclosed herein, an interlayer expansion process (a process for inserting the cation) is performed in a state where a voltage is applied to the carbon material. Thereby, the cation can be efficiently inserted into the carbon material. Therefore, the interlayer distance of the carbon material can be appropriately increased. For example, compared with the case where the carbon material is immersed in a solution containing the cation and left to stand, the effect of expanding the interlayer distance of the carbon material more efficiently (shortening the processing time, improving the expansion rate, etc.), more At least one of the effects of uniformly expanding can be realized.
The initial charging step (step of inserting the cation into the carbon material) can be performed as a part of a so-called conditioning step. Therefore, a battery with better performance (for example, output characteristics) can be manufactured without excessively complicating the manufacturing process of the existing lithium secondary battery.

  Hereinafter, experimental examples relating to the present invention will be described. However, the present invention is not intended to be limited to the specific examples.

<Experimental example 1: Production of lithium ion secondary battery>
A 18650 type lithium secondary battery was manufactured as follows.
Graphite powder (Kishida Chemical Co., Ltd. product) was used as the carbon material for the negative electrode active material. This material has a highly crystalline carbon (graphite) structure. The carbon material (negative electrode active material) was mixed with ion exchange water together with carboxymethyl cellulose (CMC) and styrene butadiene block copolymer (SBR) to prepare a paste-like negative electrode composition. The approximate mass ratio of each material (other than water) contained in this composition is 98% by mass for the carbon material, 1% by mass for CMC, and 1% by mass for SBR. This negative electrode composition is applied (attached) to both sides of a long copper foil as a negative electrode current collector, and a negative electrode active material containing layer is provided on both sides of the negative electrode current collector (negative electrode sheet) Was made.

On the other hand, lithium nickel oxide (LiNiO ₂ ) as a positive electrode active material and acetylene black as a conductive material are mixed with polytetrafluoroethylene (PTFE) and CMC with ion-exchanged water to obtain a paste-like positive electrode composition. Prepared. The approximate mass ratio of each material (other than water) contained in this composition is 95% by mass of the positive electrode active material (LiNiO ₂ ), 3% by mass of acetylene black, 1% by mass of PTFE, and 1% by mass of CMC. is there. This positive electrode composition is applied (attached) to both sides of a long aluminum foil as a positive electrode current collector, and a positive electrode active material-containing layer is provided on both sides of the positive electrode current collector (positive electrode sheet). Was made.

  As the separator, a long porous polyethylene sheet having a thickness of about 25 μm was used. The positive electrode sheet and the negative electrode sheet were stacked so as to face each other through this separator sheet, and this was wound in the longitudinal direction to produce a wound electrode body. After the obtained electrode body was accommodated in a bottomed cylindrical aluminum container, an aluminum battery lid was welded to the open end of the container. Here, the positive electrode sheet which comprises an electrode body is electrically connected with the positive electrode terminal which protrudes from a battery cover through the positive electrode current collection tab made from aluminum. Moreover, the negative electrode sheet which comprises an electrode body is electrically connected with the negative electrode terminal which protrudes from a battery cover through the copper current collection tabs.

LiPF ₆ (supporting salt) and NaPF ₆ were dissolved in a 3: 7 (volume ratio) mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) to prepare an initial electrolytic solution. The concentration of LiPF ₆ in this initial electrolyte is about 1 mol / L. The concentration of NaPF ₆ is about 0.01 mol / L. The initial electrolytic solution was injected into the battery container from a through hole (injection hole) provided in the battery lid, and then the battery container was sealed. In this way, a battery assembly was produced.

The obtained battery assembly was conditioned. That is, the positive electrode terminal and the negative electrode terminal are connected to an external power source, and first, a constant current (CC) charge is performed for 3 hours at a charge rate of 1/10 C (here, corresponding to about 50 mA), and then 1/3 C of Constant current-constant voltage (CC-CV) charging was performed up to 4.1 V at the charge rate. It is considered that at least a part of sodium ions contained in the initial electrolytic solution was inserted between the layers of the negative electrode active material (carbon material) together with the lithium ions by the initial charging step.
Thereafter, the initially charged battery assembly was discharged at a constant current (CC) to 3.0 V at a discharge rate of 1 / 3C. Furthermore, an operation of charging at a constant current-constant voltage (CC-CV) up to 4.1 V at a charge rate of 1/3 C, and an operation of discharging at a constant current (CC) of up to 3.0 V at a discharge rate of 1/3 C; Was repeated 2-3 times. In this way, the battery assembly was conditioned to obtain a lithium ion secondary battery (sample A1).

The concentrations of NaPF ₆ are about 0.03 mol / L (sample A2), about 0.05 mol / L (sample A3), about 0.08 mol / L (sample A4), and about 0.1 mol / L (sample A5). ), Except that an initial electrolytic solution of about 0.2 mol / L (sample A6) was used, and the lithium-ion secondary battery (samples A2 to A6) was prepared and conditioned in the same manner as sample A1. )

<Experimental example 2>
Samples A1 to A6 except that an initial electrolytic solution not containing NaPF ₆ (that is, an initial electrolytic solution containing LiPF ₆ at a concentration of 1 mol / L in a 3: 7 (volume ratio) mixed solvent of EC: EMC) was used. A lithium ion secondary battery (Comparative Sample A1) was obtained by preparing and conditioning a battery assembly obtained in the same manner as in Example 1.
For each battery of Samples A1 to A6 and Comparative Sample A1, frequency characteristics were obtained by the AC impedance method, and the reaction resistance component of the negative electrode was extracted from the frequency characteristics. The results are shown in FIG. The values of the reaction resistance components of Samples A1 to A6 shown in FIG. 1 and Table 1 are relative values when the reaction resistance component value of Comparative Sample A1 is 100%.

As can be seen from Figure 1 and Table 1, samples A1~A6 prepared by using the initial electrolyte containing NaPF ₆ of the support salt and 0.01~0.2mol / L of 1 mol / L does not include NaPF ₆ In any of the comparative samples A1 prepared using the initial electrolytic solution, the reaction resistance component was 10% or less. In particular, in samples A3 to A6 using the initial electrolytic solution having a Na ⁺ concentration exceeding 0.03 mol / L, the reaction resistance component was reduced by 20% or more (approximately 25%) with respect to the comparative sample A1. The effect of lowering the reaction resistance is that Na ⁺ having an ionic radius larger than that of Li ⁺ is inserted between layers of the carbon material (negative electrode active material) by charging during conditioning, thereby increasing the interlayer distance and inserting Li ⁺ . -It is thought that this was realized in connection with the decrease in energy required for desorption. A battery having a reduced reaction resistance as described above can be a battery having more excellent output characteristics (for example, a high output).
According to the results of this experimental example, the reaction resistance lowering effect was almost saturated when the Na ⁺ concentration was in the range of 0.05 mol / L or more. Therefore, it is considered appropriate to use an initial electrolytic solution whose Na ⁺ concentration is generally in the range of about 0.05 to 0.1 mol / L.

<Experimental example 3>
LiPF ₆ (supporting salt) and KPF ₆ were dissolved in a 3: 7 (volume ratio) mixed solvent of EC and EMC to prepare an initial electrolytic solution. The concentration of LiPF ₆ in this initial electrolyte is about 1 mol / L. The concentration of KPF ₆ is about 0.01 mol / L. A lithium ion secondary battery (sample B1) was obtained by preparing and conditioning the battery assembly in the same manner as sample A1, except that this initial electrolyte was used.
The concentrations of KPF ₆ are about 0.02 mol / L (sample B2), about 0.04 mol / L (sample B3), about 0.08 mol / L (sample B4), and about 0.15 mol / L (sample B5). ), Except that the initial electrolyte solution of about 0.3 mol / L (sample B6) was used, and the battery assembly was prepared and conditioned in the same manner as sample B1, thereby obtaining a lithium ion secondary battery (samples B2 to B2). B6) was obtained.

  For each battery of Samples B1 to B6 and Comparative Sample B1, frequency characteristics were obtained by the AC impedance method, and the reaction resistance component of the negative electrode was extracted from the frequency characteristics. The results are shown in FIG. The reaction resistance component values of Samples B1 to B6 shown in FIG. 2 and Table 2 are relative values when the reaction resistance component value of Comparative Sample B1 is 100%.

As can be seen from Figure 2 and Table 2, samples B1~B6 prepared using an initial electrolytic solution containing KPF ₆ of the support salt and 0.01~0.3mol / L of 1 mol / L does not comprise a KPF ₆ In any of the comparative samples B1 prepared using the initial electrolytic solution, the reaction resistance component was 10% or less. In particular, in the samples B3 to B6 using the initial electrolytic solution having a K ⁺ concentration exceeding 0.02 mol / L, the reaction resistance component was reduced by approximately 20% with respect to the comparative sample B1. The effect of reducing the reaction resistance is that K ⁺ having an ionic radius larger than that of Li ⁺ is inserted between the layers of the carbon material (negative electrode active material) by charging during conditioning, and the inter-layer distance is increased to increase the insertion / desorption of Li ^+. This is considered to be realized in connection with the decrease in energy required for separation. Thus, a battery with reduced reaction resistance can be a battery with higher output.
According to the results of this experimental example, the reaction resistance lowering effect was almost saturated in the range where the K ⁺ concentration was 0.04 mol / L or more. Therefore, it is considered appropriate to use an initial electrolytic solution whose K ⁺ concentration is usually in the range of about 0.04 to 0.1 mol / L.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
In addition, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

It is a graph which shows the relationship between the sodium ion concentration of an initial stage electrolyte solution, and the value of a reaction resistance component. It is a graph which shows the relationship between the potassium ion concentration of an initial stage electrolyte solution, and the value of a reaction resistance component.

Claims (5)

The following steps:
A battery assembly comprising: a positive electrode having a material capable of inserting / extracting lithium ions; a negative electrode having a carbon material capable of inserting / extracting lithium ions; and an initial electrolyte containing a cation having a larger ion radius than lithium ions. Obtaining a solid; and
Performing an initial charge on the battery assembly;
It encompasses,
The initial electrolytic solution contains the cation containing one or two selected from the group consisting of alkali metal ions other than lithium at a concentration of 0.002 to 0.3 mol / liter, and manufacture of a lithium secondary battery Method.   The method according to claim 1, wherein the initial electrolytic solution includes a non-aqueous solvent, a lithium salt dissolved in the solvent, and a salt of the cation.   The method according to claim 1, wherein the initial charging is performed at a charging rate of 1/3 C or less until at least SOC 20% is reached.   2. The method according to claim 1, wherein the initial charging is performed at a charging rate of 1/3 C or less until at least the cation concentration of the initial electrolytic solution is reduced to 0.03 mol / liter or less. The lithium secondary battery manufactured by the method as described in any one of Claim 1 to 4 .

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