JP2012186035A - Pretreatment method and usage method of lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pretreatment method capable of improving cycle characteristics within a short time in a lithium ion secondary battery using a solid solution positive electrode active material, and a usage method of a lithium ion secondary battery followed by the pretreatment.SOLUTION: In a lithium ion secondary battery, a positive electrode active material is used, the positive electrode active material being represented by a compositional formula: [Li][LiMnM]O(in the formula, x satisfies 0.1≤x≤0.325, and M is represented as NiαCoβMnγ where 0≤α≤0.5, 0≤β≤0.33 and 0≤γ≤0.5 are satisfied). In a pretreatment method of the lithium ion secondary battery, an upper limit voltage during charging and a lower limit voltage during discharging are controlled at a constant potential in a voltage range of 4.0 V or higher and less than 4.9 V, and 2.0 V or higher and less than 3.5 V, relative to a Li reference electrode, respectively.

Description

  The present invention relates to a pretreatment method for a lithium ion secondary battery using a solid solution system material composed of a lithium-containing composite oxide as a positive electrode active material, and a charge / discharge method after the pretreatment, that is, the use of the lithium ion secondary battery. It is about the method.

In recent years, various efforts have been made to reduce CO ₂ emissions as a measure against air pollution and global warming. In the automotive industry, CO ₂ emissions have been reduced by introducing hybrid electric vehicles and electric vehicles. High-performance secondary batteries are being developed as a power source for driving these vehicles.
Such a secondary battery for driving a motor is required to have a particularly high capacity and excellent cycle characteristics. Therefore, among various secondary batteries, a lithium ion secondary battery having high theoretical energy is used. It is attracting attention.

In order to increase the energy density in such a lithium ion secondary battery, it is necessary to increase the amount of electricity stored per unit mass of the positive electrode and the negative electrode, and the positive electrode material that may satisfy such a requirement As a result, solid solution system materials are attracting attention. Among them, a solid solution of electrochemically inactive and layered Li ₂ MnO ₃ and electrochemically active layered LiMO ₂ (wherein M is a transition metal such as Co or Ni) is 200 mAh / It is expected as a candidate for a high-capacity positive electrode material exceeding g.

  And in patent document 1, in order to improve the cycle durability of the lithium ion secondary battery using the positive electrode material of the above solid solution system, the positive electrode material is subjected to an oxidation treatment, for example, an electrode is formed. It is disclosed that the oxidation treatment is performed by charging and discharging in a potential range not exceeding a predetermined potential.

JP 2008-270201 A

  However, in the lithium ion secondary battery using the solid solution positive electrode material described in Patent Document 1, the cycle characteristics are greatly improved by performing an oxidation treatment by charge / discharge in a predetermined potential range, that is, a pre-discharge treatment. Although it can be improved, this pretreatment has a problem that it takes a long time of 5 days or more.

  The present invention has been made to solve the above-mentioned problems in lithium ion secondary batteries using a solid solution system material as a positive electrode active material. The object of the present invention is to achieve cycle characteristics in a short time. It is providing the pre-processing method of the lithium ion secondary battery which can improve this. Furthermore, it is providing the charging / discharging method following such a pretreatment, in other words, the usage method of the said lithium ion secondary battery.

  As a result of intensive studies to achieve the above object, the present inventors changed the pretreatment of the lithium ion secondary battery using the positive electrode active material made of the solid solution system material from constant current control to constant potential control. As a result, the inventors have found that the above object can be achieved and have completed the present invention.

That is, the present invention has been made based on the above findings, the pretreatment method of a lithium ion secondary battery of the present _{invention, [Li 1.5] [Li 0.5} (1-x) Mn 1-x M 1 _.5x ] O ₃ (wherein x satisfies 0.1 ≦ x ≦ 0.5, M is represented by NiαCoβMnγ, 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, 0 <γ ≦ 0.5) In the pretreatment method of the lithium ion secondary battery using the positive electrode active material represented by the composition formula, the upper limit voltage during charging is 4.0 V or more and less than 4.9 V with respect to the Li reference electrode, The lower limit voltage at the time of discharging is controlled at a constant potential within a voltage range of 2.0 V or more and less than 3.5 V.
In addition, the method of using the lithium ion secondary battery of the present invention is that the lithium ion secondary battery using the positive electrode active material is subjected to the above pretreatment by constant potential control, and then the upper limit voltage during charge / discharge is referred to Li. It is characterized in that charging / discharging is performed by controlling constant current in a voltage range of 4.3 V to less than 4.9 V and a lower limit voltage of 2.0 V to 3.0 V with respect to the electrode.

  According to the present invention, the pretreatment by the constant current control of the lithium ion secondary battery is performed by the constant potential control, and the upper limit voltage at the time of charging and the increasing / decreasing voltage at the time of discharging are performed within a predetermined range. Compared with the conventional processing by current control, the preprocessing time can be greatly shortened.

It is a graph which shows typically the difference of pre-processing (a) by constant current control and pre-processing (b) by constant potential control of a lithium ion battery, respectively. It is a graph which shows typically the pretreatment conditions of the lithium ion battery by constant potential control in the example of the present invention. It is a TEM image which compares and shows the surface state of the positive electrode active material particle after repeating 50 cycles of charging / discharging in the case where there is no pretreatment (a), and the case where pretreatment by constant potential control is performed (b).

  Below, the pre-processing method of the lithium ion secondary battery of this invention is demonstrated in detail with the structure of the lithium ion secondary battery as a process target. In the present specification, “%” represents mass percentage unless otherwise specified.

In the pretreatment method of the lithium ion secondary battery of the present invention, as described above, the predetermined composition formula [Li _1.5 ] [Li _{0.5 (1-x)} Mn _1-x M _1.5x ] O ₃ (wherein x satisfies 0.1 ≦ x ≦ 0.5, M is represented by NiαCoβMnγ, 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, 0 <γ ≦ 0.5) When a pretreatment is performed on a lithium ion secondary battery using a solid solution system positive electrode active material represented by the formula, the upper limit voltage during charging is 4.0 V or more and less than 4.9 V with respect to the Li reference electrode, and the lower limit during discharge. The voltage is controlled to a constant potential within a voltage range of 2.0 V or more and less than 3.5 V.

In the pretreatment method of the present invention, the upper limit voltage during charging is set to 4.0 V or more and less than 4.9 V. When the upper limit voltage during charging is less than 4.0 V, it is activated electrochemically. In the case of 4.9 V or more, the electrolyte solution used is decomposed and the battery characteristics are deteriorated.
On the other hand, the lower limit voltage during discharge is set to 2.0 V or more and less than 3.5 V. If the lower limit voltage during discharge is less than 2.0 V, an overdischarge state occurs. In some cases, sufficient Li is not inserted, so that the structural change does not occur and the electrochemical activation is not caused.

  In the pretreatment method of the present invention, from the viewpoint of avoiding a sudden structural change of the positive electrode active material during the treatment, the upper limit voltage during charging is 0.01 V or more and less than 1.0 V every 10 or less charge / discharge cycles. It is desirable that the voltage is increased gradually or the lower limit voltage during discharge is decreased by 0.01 V or more and less than 1.0 V.

Further, in the method of using the lithium ion secondary battery of the present invention, the lithium ion secondary battery using the positive electrode active material is subjected to the above pretreatment method by constant potential control, and then the upper limit voltage during charging and discharging. Is charged and discharged with constant current control in a voltage range of 4.3 V to less than 4.9 V and a lower limit voltage of 2.0 V to 3.0 V with respect to the Li reference electrode.
Here, the upper limit voltage during charging / discharging is set to 4.3 V or more and less than 4.9 V. If the upper limit voltage is less than 4.3 V, there is a possibility that the electrochemical activation may not be sufficiently performed. In the case of 4.9 V or more, the electrolyte solution used is decomposed and the battery characteristics are deteriorated. Further, when the lower limit voltage is less than 2.0V, an overdischarge state occurs. When the lower limit voltage exceeds 3.0V, sufficient Li is not inserted, so that no structural change occurs and it is not electrochemically activated. This is due to problems.

  The voltage range of constant potential control in the pretreatment is such that the upper limit voltage during charging is 4.3 V or more and 4.8 V with respect to the Li reference electrode from the viewpoint of preventing cracks due to abrupt structural change of the positive electrode active material. On the other hand, it is desirable that the lower limit voltage during discharge is in the range of 2.5V to less than 3.0V.

  In the present invention, the reason why the pretreatment can be completed in a short time by performing the constant potential control is not necessarily clear, but the difference between the constant current control and the pretreatment by the constant potential control is schematically shown in FIG. It is thought to become.

That is, while constant current control (FIG. 1A) takes time to increase to the reaction potential, in constant potential control (FIG. 1B), pretreatment can be started from the reaction potential. This is considered to be due to the fact that the time for increasing the reaction potential is greatly shortened.
Note that the reaction potential refers to a potential at which the material undergoes a structural change with the separation of Li and causes an electrochemically active reaction. When the reaction is carried out at a high potential from the time of the first charge, the structure changes with the rapid release of Li, which causes the generation of cracks and eventually deteriorates to cause the surface layer to become amorphous. Since the pre-treatment gradually advances this structural change, it is considered that a stable surface layer is generated and deterioration of durability is suppressed.

  Next, the configuration and materials of the lithium ion secondary battery that is a pretreatment target of the present invention will be described.

  Generally, a lithium ion secondary battery has a battery case in which a positive electrode obtained by applying a positive electrode active material or the like to a positive electrode current collector and a negative electrode obtained by applying a negative electrode active material or the like to a negative electrode current collector are connected via an electrolyte layer. It has a structure housed inside.

[Positive electrode]
In a lithium ion secondary battery, the positive electrode is a positive electrode active material layer, that is, a positive electrode on one or both sides of a current collector (positive electrode current collector) made of a conductive material such as an aluminum foil, a copper foil, a nickel foil, or a stainless steel foil. A structure in which a positive electrode active material layer including a conductive additive and a binder is formed as necessary together with the active material is provided.
In the lithium ion secondary battery as the pretreatment target of the present invention, the positive electrode active material includes a composition formula [Li _1.5 ] [Li _{0.5 (1-x)} Mn _1-x M _1.5x ] O _3. (Wherein x satisfies 0.1 ≦ x ≦ 0.5, M is represented by NiαCoβMnγ, 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, 0 <γ ≦ 0.5) The material of the solid solution system represented is used.

As such a complex oxide, a commercially available product is used. If there is no commercially available product, for example, a compound synthesized by a solid phase method or a solution method (mixed hydroxide method, complex carbonate method, etc.) is used. Can be used.
Among these synthesis methods, it is desirable to employ a composite carbonate method because the yield is high, and since it is an aqueous solution system, a uniform composition can be obtained and composition control is easy. In addition, it can be produced by a general synthesis method such as a coprecipitation method, a sol-gel method, or a PVA method.

In the composition formula representing the composite oxide, as described above, x in the formula needs to be 0.1 to 0.5. When x exceeds 0.5, a discharge capacity of 200 mAh / g or more cannot be obtained, and a sufficient effect in terms of capacity cannot be obtained as compared with a known layered positive electrode active material. If x is less than 0.1, the composition may be close to Li ₂ MnO ₃ and charge / discharge may not be possible.

For M in the composition formula represented by NiαCoβMnγ, α must be greater than 0 and not greater than 0.5, β must be 0 to 0.33, γ must be greater than 0 and not greater than 0.5, and α + β + γ must be 1. . That is, in order for the positive electrode active material made of the composite oxide to exhibit a high capacity, Ni needs to be in a divalent state, and when α is in the above range, Ni is in a divalent state and two electrons. By reacting (Ni ²⁺ ← → Ni ⁴⁺ ).
In addition, in order for Ni to undergo a two-electron reaction in a divalent state even when trivalent Co is added, β must be in the range of 0 to 0.33, and tetravalent Mn is added, Similarly, in order for Ni to undergo a two-electron reaction in a divalent state, the value of γ needs to be in the range of 0 to 0.5 or less. The Co is added as necessary for the purpose of improving the purity of the material and improving the electronic conductivity.

In addition, about M of Chemical formula (1), following Formula Ni (alpha) Co (beta) Mn (gamma) M1 (sigma)
(Α, β, γ, σ in the formula satisfy 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, 0 <γ ≦ 0.5, 0 ≦ σ ≦ 0.1, and α + β + γ + σ = 1 is satisfied, and M1 is at least one selected from the group consisting of Al, Fe, Cu, Mg, and Ti).

In this case, the reasons for limiting the numerical values of α, β, and γ are the same as above, but it is preferable that σ satisfies 0 ≦ σ ≦ 0.1.
When σ exceeds 0.1, the reversible capacity of the positive electrode active material may be lowered. As M1, among the above elements, Al and Ti can be preferably used.
In general, nickel (Ni), cobalt (Co), and manganese (Mn) are used in terms of improving material purity and electronic conductivity, aluminum (Al), iron (Fe), copper (Cu), magnesium (Mg) and Titanium (Ti) is known to contribute to capacity and output characteristics from the viewpoint of improving the stability of the crystal structure.

  In addition, although it does not specifically limit as a particle size of the said positive electrode active material, In general, it is so desirable that it is fine, and if the work efficiency, the ease of handling, etc. are considered, if it is about 1-30 micrometers in average particle diameter, It is preferable that the thickness is about 5 to 20 μm.

As the positive electrode active material in the present invention, an active material of a solid solution system represented by the above composition formula [Li _1.5 ] [Li _{0.5 (1-x)} Mn _1-x M _1.5x ] O ₃ is used. Although it is an essential component, there is no problem even if other positive electrode active materials are used in combination.
Examples of such positive electrode active materials include lithium-transition metal composite oxides, lithium-transition metal phosphate compounds, lithium-transition metal sulfate compounds, ternary systems, NiMn systems, NiCo systems, and spinel Mn systems. Is mentioned.

Examples of the lithium-transition metal composite oxide include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni, Mn, Co) O ₂ , Li (Li, Ni, Mn, Co) O ₂ , LiFePO ₄ and Examples include those in which some of these transition metals are substituted with other elements.
Examples of the ternary system include nickel / cobalt / manganese (composite) positive electrode materials. Examples of the spinel Mn system include LiMn ₂ O ₄ . Examples of the NiMn system include LiNi _0.5 Mn _1.5 O ₄ . Examples of the NiCo system include Li (NiCo) O ₂ .

These positive electrode active materials can also be used in combination.
In addition, in the case where the optimum particle diameter is different in expressing the respective intrinsic effects of these positive electrode active materials, the optimum particle diameters may be blended and used for expressing the respective intrinsic effects, It is not always necessary to make the particle sizes of all active materials uniform.

  The thickness of the current collector is not particularly limited and is generally preferably about 1 to 30 μm. Further, the mixing ratio of these positive electrode active material, conductive additive, and binder in the positive electrode active material layer is not particularly limited.

The binder is added for the purpose of maintaining the electrode structure by binding the active materials or the active material and the current collector.
Examples of such a binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), polymethyl acrylate (PMA), Thermosetting resins such as polymethyl methacrylate (PMMA), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP) and polyacrylonitrile (PAN), epoxy resins, polyurethane resins, and urea resins In addition, rubber-based materials such as styrene butadiene rubber (SBR) can be used.

The conductive assistant is also referred to as a conductive agent, and refers to a conductive additive that is blended to improve conductivity. The conductive aid used in the present invention is not particularly limited, and conventionally known ones can be used, and examples thereof include carbon black such as acetylene black, and carbon materials such as graphite and carbon fiber.
By containing a conductive additive, an electronic network inside the active material layer is effectively formed, which contributes to improving the output characteristics of the battery and improving reliability by improving the liquid retention of the electrolytic solution.

[Negative electrode]
On the other hand, the negative electrode, like the positive electrode, is formed on one or both sides of a current collector (negative electrode current collector) made of the conductive material as described above together with the negative electrode active material, if necessary. It has a structure in which a negative electrode active material layer containing a conductive additive and binder similar to the case is formed.
The negative electrode active material applied to the lithium ion secondary battery of the present invention is not particularly limited as long as it can reversibly occlude and release lithium, and a conventionally known negative electrode active material can be used.

For example, high crystalline carbon graphite (natural graphite, artificial graphite, etc.), low crystalline carbon (soft carbon, hard carbon), carbon black (Ketjen black, acetylene black, channel black, lamp black, oil furnace black, Thermal black, etc.), carbon materials such as fullerene, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon fibril, Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl, and the like, and simple elements of these elements and these elements Oxide containing silicon (silicon monoxide (SiO), SiOx (0 x <2), tin dioxide _{(SnO 2), SnO x (} 0 <x <2), etc. SnSiO ₃₎ and carbides (such as silicon carbide (SiC)) or the like, a metal material such as lithium metal, a lithium - titanium composite oxide And lithium-transition metal composite oxides such as lithium titanate (Li ₄ Ti ₅ O ₁₂ ). In addition, these negative electrode active materials can be used alone or in the form of a mixture of two or more.

  In the above description, the positive electrode active material layer and the negative electrode active material layer are described as being formed on one or both surfaces of each current collector. However, the positive electrode active material layer is formed on one surface of one current collector. A negative electrode active material layer can be formed on the other surface, respectively, and such an electrode is applied to a bipolar battery.

(Electrolyte layer)
The electrolyte layer is a layer containing a non-aqueous electrolyte, and the non-aqueous electrolyte contained in the electrolyte layer functions as a lithium ion carrier that moves between the positive and negative electrodes during charge and discharge.
The thickness of the electrolyte layer is preferably as thin as possible from the viewpoint of reducing internal resistance, and is usually in the range of about 1 to 100 μm, preferably 5 to 50 μm.

  The nonaqueous electrolyte is not particularly limited as long as it can exhibit such a function, and a liquid electrolyte or a polymer electrolyte can be used.

The liquid electrolyte has a form in which a lithium salt (electrolyte salt) is dissolved in an organic solvent. Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), Examples include carbonates such as methylpropyl carbonate (MPC).
As the lithium _{salt, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiAsF 6, LiTaF 6, LiClO 4, LiCF 3 SO 3 , etc. A compound that can be added to the active material layer of the electrode can be employed.

On the other hand, the polymer electrolyte is classified into a gel polymer electrolyte containing an electrolytic solution (gel electrolyte) and an intrinsic polymer electrolyte containing no electrolytic solution.
The gel polymer electrolyte preferably has a structure in which the liquid electrolyte is injected into a matrix polymer (host polymer) made of an ion conductive polymer. The use of a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and it is easy to block ion conduction between the layers.

The ion conductive polymer used as the matrix polymer (host polymer) is not particularly limited, and examples thereof include polyethylene oxide (PEO), polypropylene oxide (PPO), polyvinylidene fluoride (PVDF), polyvinylidene fluoride and hexafluoropropylene. Examples of the copolymer include PVDF-HFP, polyethylene glycol (PEG), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and copolymers thereof.
Here, the ion conductive polymer may be the same as or different from the ion conductive polymer used as the electrolyte in the active material layer, but is preferably the same. The type of the electrolytic solution (lithium salt and organic solvent) is not particularly limited, and an electrolyte salt such as the lithium salt exemplified above and an organic solvent such as carbonates are used.

  The intrinsic polymer electrolyte is formed by dissolving a lithium salt in the above matrix polymer and does not contain an organic solvent. Therefore, by using an intrinsic polymer electrolyte as the electrolyte, there is no fear of liquid leakage from the battery, and the reliability of the battery is improved.

The matrix polymer of gel polymer electrolyte or intrinsic polymer electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form such a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam is applied to a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte, using an appropriate polymerization initiator. A polymerization process such as polymerization may be performed.
The non-aqueous electrolyte contained in these electrolyte layers may be a single type consisting of only one type or a mixture of two or more types.

In addition, when an electrolyte layer is comprised from a liquid electrolyte or a gel polymer electrolyte, a separator is used for the electrolyte layer.
Specific examples of the separator include a microporous film made of polyolefin such as polyethylene or polypropylene.

[Battery shape]
The lithium ion secondary battery has a battery element (electrode structure) in which the positive electrode and the negative electrode as described above are connected via an electrolyte layer, and the battery element can be used as a can or a laminate container (packaging body). It has a structure housed in a battery case.
The battery element is roughly divided into a wound battery having a structure in which a positive electrode, an electrolyte layer, and a negative electrode are wound, and a positive electrode, an electrolyte layer, and a negative electrode are stacked batteries, and the above bipolar battery is a stacked battery. It has a structure.
Moreover, it may be called what is called a coin cell, a button battery, a laminate battery, etc. according to the shape and structure of a battery case.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.

[1] Synthesis of solid solution positive electrode active material A solid solution composed of a lithium-containing composite oxide was synthesized by a composite carbonate method as a positive electrode active material.
First, as a starting material, nickel sulfate, cobalt sulfate, and manganese sulfate were weighed so that Ni, Co, and Mn had a predetermined molar ratio and dissolved in ion-exchanged water to prepare a mixed aqueous solution.

Next, aqueous ammonia was added dropwise to the mixed aqueous solution until the pH reached 7, and a sodium carbonate aqueous solution was further added dropwise to precipitate a nickel-cobalt-manganese composite carbonate. During the dropwise addition of the aqueous sodium carbonate solution, the pH was maintained at 7 with aqueous ammonia.
The obtained composite carbonate was suction filtered, washed with water, dried, and baked at a temperature of 700 ° C. to obtain a nickel-cobalt-manganese oxide.

Then, lithium hydroxide was added to the obtained composite oxide, mixed for 30 minutes in an automatic mortar, and then baked at 900 ° C. for 12 hours in the air, whereby Li _1.5 [Ni _0.25 Li _{0. 3} Co _0.1 Mn _0.85 ] O ₃ (x = 0.4, α = 0.417, β = 0.166, γ = 0.417), and Li _1.5 [Ni _0.225 Li _{0 .3} Co _0.15 Mn _0.825 ] O ₃ (x = 0.4, α = 0.375, β = 0.25, γ = 0.375) and a positive electrode having two component compositions Each active material was synthesized (see Table 1).

[2] Production of battery The positive electrode active material obtained above, acetylene black as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder were blended so as to have a mass ratio of 85: 10: 5. A positive electrode slurry was prepared by adding N-methylpyrrolidone (NMP) as a solvent and diluting it.
This slurry was applied onto an Al foil as a positive electrode current collector so that the amount of active material per unit area was about 10 mg, and a positive electrode having a diameter of 15 mm was obtained.

The positive electrode dried for 4 hours with a dryer at 120 ° C. and the negative electrode made of metallic lithium are opposed to each other through two 20 μm-thick polypropylene porous membranes, stacked on the bottom of the coin cell, and insulation between the positive and negative electrodes In order to maintain the properties, a gasket was attached.
On the other hand, LiPF ₆ (lithium hexafluorophosphate) is dissolved to a concentration of 1M in a mixed nonaqueous solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 1: 2. An electrolyte solution was prepared, and this electrolyte solution was injected using a syringe. And after laminating | stacking a spring and a spacer, the upper part of the coin cell was piled up and crimped, and the lithium ion battery was produced.

[3] Pretreatment Each of the batteries prepared above was pretreated by constant potential control and constant current control.
[3-1] Pretreatment by constant potential control (Examples 1 and 2)
The batteries prepared using the above two types of positive electrode active materials were respectively connected to a charge / discharge device, and as shown in Table 1 and FIG. 2, the initial applied potential was set to 4.4 V and charged at a constant potential for 5 minutes. The applied potential was set to 2.5 V, and constant potential discharge was performed for 5 minutes, and this was repeated twice. Next, the applied potential was changed to 4.5V, 4.6V, and further 4.7V, and the same constant potential charging / discharging was performed twice each.

[3-2] Pretreatment by constant current control (Comparative Example 1)
A battery manufactured using a solid solution positive electrode active material having a composition of Li _1.5 [Ni _0.25 Li _0.3 Co _0.1 Mn _0.85 ] O ₃ was connected to a charge / discharge device, and Table 2 As shown in the figure, constant current charging was performed at a current rate of 1/12 C until the potential difference reached 4.5 V, and then constant current discharge was performed until the potential difference reached 2.0 V, which was repeated twice. Next, this potential difference was changed to 4.6 V, 4.7 V, and 4.8 V, and the same constant current charging / discharging was performed twice each.

[4] Evaluation of battery cycle characteristics The batteries subjected to the above pretreatment were subjected to a charge / discharge test of 50 cycles under constant current control, and the capacity retention rate was investigated. That is, charging and discharging were performed at a constant current rate (1 / 12C) by charging until the maximum voltage was 4.8 V and discharging until the minimum voltage of the battery was 2.0 V. For comparison, a similar investigation was performed on a battery not subjected to pretreatment (Comparative Example 2).

The results are shown in Table 3. In the table, “capacity maintenance ratio” is a percentage of the discharge capacity at the 50th cycle to the discharge capacity at the first cycle.
Further, as representative examples of the above examples and comparative examples, positive electrode active material particles in the batteries of Comparative Example 2 (no pretreatment) and Example 1 (constant potential control pretreatment) after 50 cycles of charge and discharge were repeated. FIGS. 3A and 3B show transmission electron microscope (TEM) images, respectively.

As a result, when the charge / discharge pretreatment is performed by the constant potential control, the time required for the pretreatment is substantially shortened (about 1/90), but is almost the same as the case of the constant current control. It was confirmed that the maintenance rate was obtained. The reason for this is considered as follows.
From the TEM image shown in FIG. 3, when the pretreatment is not performed (a), the amorphous state in the vicinity of the surface of the active material particles is progressing, whereas when the pretreatment is performed (b) Such a phenomenon is not observed, and it can be seen that the pretreatment prevents the surface of the active material particles from being amorphous.

  That is, the deterioration phenomenon of the solid solution positive electrode active material material due to repeated charge and discharge occurs from the surface. Therefore, the surface of the positive electrode active material particles can be reacted even at constant potential control where it is difficult to react in the bulk, thereby improving the surface deterioration and improving the durability of the positive electrode active material. It is thought that it can be made to.

Claims (5)

When pre-treating a lithium ion secondary battery using a positive electrode active material represented by the following composition formula, the upper limit voltage during charging is 4.0 V or more and less than 4.9 V with respect to the Li reference electrode, and the lower limit during discharging. A pretreatment method for a lithium ion secondary battery, wherein the voltage is controlled at a constant potential in a voltage range of 2.0 V or more and less than 3.5 V.
[Li _1.5 ] [Li _{0.5 (1-x)} Mn _1-x M _1.5x ] O ₃
(Wherein x satisfies 0.1 ≦ x ≦ 0.5, M is represented by NiαCoβMnγ, 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, 0 <γ ≦ 0.5)   2. The pretreatment method according to claim 1, wherein the upper limit voltage during charging is increased by 0.01 V or more and less than 1.0 V every 10 or less charge / discharge repetitions.   3. The pretreatment method according to claim 1, wherein the lower limit voltage during discharge is decreased by 0.01 V or more and less than 1.0 V every 10 or less charge / discharge repetitions.   After performing the pretreatment according to any one of claims 1 to 3, the upper limit voltage during charging and discharging is 4.3 V or more and less than 4.9 V with respect to the Li reference electrode, and the lower limit voltage is 2.0 V. A method for using a lithium ion secondary battery, wherein charging and discharging are performed under constant current control in a voltage range of 3.0 V or less.   The upper limit voltage during charging in the pretreatment is 4.3 V or more and less than 4.8 V with respect to the Li reference electrode, and the lower limit voltage during discharging is in a voltage range of 2.5 V or more and less than 3.0 V. 4. A method of using the lithium ion secondary battery according to 4.

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