JP2014130774A - Nonaqueous electrolyte secondary battery and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having excellent durability, and to provide a manufacturing method therefor.SOLUTION: A nonaqueous electrolyte secondary battery 100 comprises: a positive electrode 10; a negative electrode 20; and a nonaqueous electrolyte 90. The positive electrode 10 comprises a positive electrode active material particles having an actuation upper limit potential of 4.5 V or more with reference to metal lithium; and a basic composition of a lithium transition metal compound. The positive electrode active material particles include a center region having the basic composition, and an outer region covering the outside of the center region. The outer region does not contain at least one kind of transition metal contained in the basic composition, or the concentration of transition metal is lower than that of the basic composition. The nonaqueous electrolyte 90 contains a transition metal ion scavenger.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and a method for manufacturing the same.

  As part of improving the performance of non-aqueous electrolyte secondary batteries, higher energy density is required. The use of a positive electrode active material having a higher operating potential is one of effective means for increasing the energy density of the nonaqueous electrolyte secondary battery. For example, Patent Document 1 describes a positive electrode active material for a non-aqueous secondary battery made of a spinel type lithium nickel manganese composite oxide that exhibits an operating voltage of 4.5 V or more with respect to a Li potential reference. Other technical documents related to the nonaqueous electrolyte secondary battery include Patent Documents 2 and 3.

JP 2002-158008 A JP 2011-187193 A JP 2000-195548 A

However, the performance of secondary batteries using spinel type lithium nickel manganese composite oxide as the positive electrode active material tends to deteriorate. For example, the battery is charged under the condition of being charged until the potential of the positive electrode is 4.5 V or higher with respect to the metallic lithium (hereinafter, the potential based on the metallic lithium is sometimes referred to as “vs. Li ^/ Li ⁺ ”). When the discharge is repeated, the battery capacity may greatly decrease as the number of charge / discharge increases. For this reason, it has been desired to improve the durability of a non-aqueous electrolyte secondary battery using a positive electrode active material having a high operating potential.

  Then, an object of this invention is to provide the nonaqueous electrolyte secondary battery excellent in durability. Another related object is to provide a method for producing such a non-aqueous electrolyte secondary battery.

The present inventors paid attention to an event in which a transition metal element (for example, manganese (Mn)) contained in the positive electrode active material is eluted into the non-aqueous electrolyte as a cause of the deterioration of the battery performance as described above. The eluted transition metal element can be deposited on the negative electrode, leading to a decrease in battery capacity. In this regard, Patent Document 3 discloses a non-aqueous solution to the problem that when a composite oxide represented by Li _x Mn _y O ₂ is used as a positive electrode active material, Mn is eluted from the positive electrode and the cycle life is shortened. It is described that a chelating agent or a crown ether that forms a complex with Mn is contained in the electrolytic solution, thereby trapping Mn ions eluted from the positive electrode active material and suppressing the precipitation of Mn on the negative electrode ( Patent Literature 3, paragraphs 0003 and 0017).

However, according to the study by the present inventors, in a non-aqueous electrolyte secondary battery in which the operating potential of the positive electrode can be 4.5 V (vs. Li ^/ Li ⁺ ) or higher, for example, acetylacetone is used as a chelating agent for the non-aqueous electrolyte. It has been found that when it is contained, the capacity deterioration due to charging / discharging becomes remarkable as compared with the nonaqueous electrolyte secondary battery not containing the chelating agent.

  Therefore, the present inventors have further studied and found that chelating agents such as acetylacetone can degrade battery performance by being oxidatively decomposed on the positive electrode side. Then, in the positive electrode including the positive electrode active material particles, the potential of the surface of the positive electrode active material particles (that is, the interface between the positive electrode active material particles and the electrolyte) is made lower than the potential of the central portion, whereby The present invention has been completed by finding that the effects of including the above can be appropriately exhibited to solve the above problems.

According to this specification, a nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte is provided. The positive electrode includes positive electrode active material particles having a lithium transition metal compound as a basic composition. The upper limit operating potential of the positive electrode is typically 4.5 V (vs. Li ^/ Li ⁺ ) or more. The positive electrode active material particles include a central region having the basic composition and an outer region covering the outside of the central region. The outer region does not contain at least one kind of transition metal (for example, Mn) contained in the basic composition, or is a region where the concentration of the transition metal is lower than the basic composition. The non-aqueous electrolyte contains a transition metal ion scavenger (for example, acetylacetone).

  In the non-aqueous electrolyte secondary battery having such a configuration, the positive electrode active material particles have an outer region covering the central region, whereby the surface potential of the positive electrode active material particles can be made lower than the central region. Thereby, the event that the transition metal ion scavenger contained in the non-aqueous electrolyte is decomposed at the positive electrode can be suppressed, and the transition metal ion scavenger can appropriately exert its effect. As a result, a non-aqueous electrolyte secondary battery with improved durability can be realized. In addition, such a nonaqueous electrolyte secondary battery is preferable because the operating upper limit potential of the positive electrode is high and the energy density can be high.

Here, the “non-aqueous electrolyte secondary battery having an operating upper limit potential of the positive electrode of 4.5 V (vs. Li ^/ Li ⁺ ) or higher” means that the SOC (State of Charge) is in the range of 0% to 100%. A non-aqueous electrolyte secondary battery having a region where the oxidation-reduction potential (operating potential) of the positive electrode active material is 4.5 V (vs. Li ^/ Li ⁺ ) or higher. Such a battery can also be grasped as a non-aqueous electrolyte secondary battery in which the potential of the positive electrode is 4.5 V (vs. Li ^/ Li ⁺ ) or higher in at least a part of SOC 0% to 100%.

The technique disclosed here is, for example, an aspect in which the outer region of the positive electrode active material particle is a coating layer having lithium ion conductivity (for example, a coating layer including a solid electrolyte such as Li ₃ PO ₄ ). It can be implemented preferably.

In a preferred embodiment, the basic composition is a spinel structure lithium nickel manganese oxide. The positive electrode active material particles having such a composition are suitable as a constituent material of a non-aqueous electrolyte secondary battery in which the positive electrode operating upper limit potential (vs. Li ^/ Li ⁺ ) is 4.5 V or more.

In a preferred embodiment of the method disclosed herein, the basic composition may be a composition represented by the following general formula (1).
_{Li x (Ni 0.5-a Fe} P Mn 1.5-b Ti Q M 0 R) O 4 + d (1)
Here, x in the general formula (1) may satisfy 0.9 ≦ x ≦ 1.2. a may be 0 ≦ a. b may be −0.1 ≦ b. P may be 0 <P ≦ 0.1. Q may be 0 <Q ≦ 0.1. M ⁰ can be an element (typically a metal element) other than Ni, Mn, Fe, and Ti. R may be 0 ≦ R. a, b, P, Q, and R may be values satisfying a + b = P + Q + R. d may be a value that satisfies −0.2 ≦ d ≦ 0.2 and satisfies the charge neutrality condition. According to the positive electrode active material particles having such a basic composition, a more durable nonaqueous electrolyte secondary battery can be realized.

According to this specification, there is also provided a method for producing a non-aqueous electrolyte secondary battery in which the operating upper limit potential (vs. Li ^/ Li ⁺ ) of the positive electrode is 4.5 V or more. The manufacturing method includes preparing a positive electrode including positive electrode active material particles having a lithium transition metal compound as a basic composition. It also includes providing a non-aqueous electrolyte containing a transition metal ion scavenger. Furthermore, it includes constructing a non-aqueous electrolyte secondary battery using the positive electrode and the non-aqueous electrolyte. Here, the positive electrode active material particles include a central region having the basic composition and an outer region covering the outside of the central region. The outer region does not contain at least one transition metal contained in the basic composition, or is a region where the concentration of the transition metal is lower than the basic composition.
In the nonaqueous electrolyte secondary battery produced by such a method, the positive electrode active material particles are used, so that the transition metal ion scavenger contained in the nonaqueous electrolyte can appropriately exert its effect. As a result, a non-aqueous electrolyte secondary battery with improved durability can be realized. In addition, such a nonaqueous electrolyte secondary battery is preferable because the operating upper limit potential of the positive electrode is high and the energy density can be high.

  Non-aqueous electrolyte secondary batteries disclosed herein (including non-aqueous electrolyte secondary batteries manufactured by any of the methods disclosed herein, the same shall apply hereinafter) may exhibit good durability. . For example, even if charging / discharging is repeated under a temperature environment higher than room temperature (for example, 50 ° C. to 60 ° C.), the capacity can be reduced little. In addition, the energy density can be high. Therefore, taking advantage of such characteristics, for example, it can be suitably used as a power source (drive power source) of a hybrid vehicle or an electric vehicle. A typical example of the hybrid vehicle is a vehicle including both an engine (internal combustion engine) and a motor drive battery as power sources.

It is a perspective view which shows typically the external shape of the nonaqueous electrolyte secondary battery which concerns on one Embodiment. It is the II-II sectional view taken on the line of FIG. It is a schematic diagram which shows the winding electrode body of the nonaqueous electrolyte secondary battery which concerns on one Embodiment. It is a side view which shows typically the vehicle (automobile) provided with the non-aqueous secondary battery.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In the following drawings, members / parts having the same action are described with the same reference numerals, and redundant descriptions may be omitted or simplified. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

In this specification, “secondary battery” refers to a general power storage device that can be repeatedly charged and discharged, and is a term that includes a so-called storage battery such as a lithium secondary battery and a power storage element such as an electric double layer capacitor. Further, the “non-aqueous electrolyte secondary battery” refers to a battery provided with a non-aqueous electrolyte (typically, an electrolyte that exhibits a liquid state at room temperature (for example, 25 ° C.), that is, an electrolytic solution). The non-aqueous electrolyte may be, for example, a non-aqueous electrolyte in a form containing a supporting salt (supporting electrolyte) in a non-aqueous solvent. In addition, the “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by movement of lithium ions between the positive and negative electrodes. A secondary battery generally called a lithium ion secondary battery, a lithium ion capacitor, or the like is a typical example included in the lithium secondary battery in this specification. An “active material” refers to a material that can reversibly occlude and release (typically insertion and desorption) chemical species that serve as charge carriers in a secondary battery. The chemical species serving as the charge carrier is mainly lithium ions in a lithium secondary battery (for example, a lithium ion secondary battery).
In the present specification, the “lithium transition metal compound” refers to a compound containing lithium and at least one transition metal as constituent elements, and further includes a compound containing another element (typical metal element and / or nonmetal element). It means to include. In this specification, “lithium manganese oxide” means an oxide containing at least lithium and manganese as constituent elements, and further includes oxides containing other metal elements and / or nonmetal elements. is there. Similarly, in this specification, “lithium nickel manganese oxide” refers to an oxide containing at least lithium, nickel and manganese as constituent elements, and further includes an oxide containing another metal element and / or a nonmetal element. It means to include.

In this specification, “SOC” (State of Charge) refers to the state of charge of a battery based on a voltage range in which the battery is normally used unless otherwise specified. For example, in a battery in which the voltage between terminals (open circuit voltage (OCV)) is in the range of 4.9 V (upper limit voltage) to 3.5 V (lower limit voltage), the rating measured in the voltage range It shall be the state of charge based on capacity.
In this specification, “1C” means a current value that discharges a fully charged battery (SOC 100%) to a discharge end voltage (SOC 0%) in one hour.
In the present specification, the “average particle diameter” refers to a median diameter (D50) in a volume-based particle size distribution obtained by a general laser diffraction particle size distribution measuring device unless otherwise specified.

  The technology disclosed herein can be applied to various nonaqueous electrolyte secondary batteries including a positive electrode including a lithium transition metal compound and the production thereof. The nonaqueous electrolyte secondary battery typically includes an electrode body including the positive electrode and the negative electrode, a nonaqueous electrolyte, and a battery case that houses the electrode body and the nonaqueous electrolyte. Hereinafter, the constituent elements of such a battery will be sequentially described.

<Positive electrode>
The positive electrode in the technique disclosed herein has a working potential (vs. Li ^/ Li ⁺ ) in a partial range of at least SOC 0% to 100%, and a general non-aqueous electrolyte secondary battery (upper working potential is 4). .1V to about 4.2V), typically about 4.5V or more. A positive electrode exhibiting such an operating upper limit potential can be realized by using a positive electrode active material having a maximum operating potential (vs. Li ^/ Li ⁺ ) at SOC ⁰ % to 100% of 4.5 V or more.

Here, the working potential of the positive electrode active material can be measured, for example, as follows. Specifically, a positive electrode containing a positive electrode active material to be measured is used as a working electrode (WE), the working electrode, metallic lithium as a counter electrode (CE), metallic lithium as a reference electrode (RE), and use A non-aqueous electrolyte (for example, an electrolytic solution containing LiPF ₆ at a concentration of 1 M in a mixed solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a ratio of EC: EMC = 30: 70 on a volume basis); A tripolar cell is constructed using,. The SOC value of this cell is adjusted in increments of 5% from 0% to 100% SOC based on the theoretical capacity of the cell. Such SOC adjustment can be performed by constant current charging between WE and CE using, for example, a general charging / discharging device or a potentiostat. Then, the potential between WE and RE after the cells adjusted to the respective SOC values are left for 1 hour is measured, and the potential is determined based on the operating potential (vs. Li ^/ Li ⁺ ) of the positive electrode active material at the SOC value. And

In general, the operating potential of the positive electrode active material is highest in a range between SOC 0% and 100% in a range including SOC 100%. Therefore, normally, the operating potential of the positive electrode active material at SOC 100% (that is, fully charged state) is normal. Thus, the upper limit (for example, whether it is 4.5 V or more) of the operating potential of the positive electrode active material can be grasped. The operating potential (vs. Li ^/ Li ⁺ ) of the positive electrode active material at 100% SOC is preferably higher than 4.5V, for example, 4.7V or higher. In the technique disclosed herein, typically, the operating potential (vs. Li ^/ Li ⁺ ) of the positive electrode active material at 100% SOC is 7.0 V or less (typically 6.0 V or less, for example, 5.5 V or less. The non-aqueous electrolyte secondary battery is preferably applied.

<Positive electrode active material particles>
The positive electrode has a basic composition of a lithium transition metal compound (typically, a lithium transition metal oxide) that can function as a positive electrode active material having an operating potential (vs. Li ^/ Li ⁺ ) of 4.5 V or higher. Provide material particles. For example, positive electrode active material particles containing a lithium transition metal compound having an operating potential (vs. Li ^/ Li ⁺ ) higher than 4.5 V (further higher than 4.6 V, for example, higher than 4.7 V) are preferable.

  The technique disclosed here can be preferably implemented in an embodiment in which the basic composition of the positive electrode active material particles is a lithium transition metal compound containing at least Mn. For example, in terms of the number of atoms, 50% or more of the transition metals contained in the basic composition is preferably Mn. The positive electrode active material particles having such a basic composition mainly use Mn, which is an abundant and inexpensive metal resource, and is preferable from the viewpoint of reducing raw material costs and raw material supply risks. Further, a positive electrode active material containing Mn (for example, a lithium manganese compound having a spinel structure) tends to easily elute Mn from the positive electrode active material. For this reason, it is particularly meaningful to apply the technique disclosed herein to suppress the phenomenon in which eluted Mn precipitates at the negative electrode.

As a suitable example of the lithium transition metal compound that can function as the positive electrode active material exhibiting the above-described operating potential, a lithium manganese oxide having a spinel structure (hereinafter, the spinel structure may be referred to as “spinel type”) may be mentioned. More specifically, the following general formula:
_{Li x Mn 2-y M '} y O 4 + d (F1);
The spinel type lithium manganese oxide represented by these is mentioned.
Here, x may be 0.9 ≦ x ≦ 1.2. y is 0 ≦ y <2, typically 0 ≦ y ≦ 1 (eg, 0.2 ≦ y ≦ 0.6). d is a value that satisfies −0.2 ≦ d ≦ 0.2 and satisfies the charge neutrality condition. When y is larger than 0 (0 <y), M ′ may be one or more selected from any metal element or nonmetal element other than Mn. More specifically, lithium (Li), sodium (Na), magnesium (Mg), calcium (Ca), strontium (Sr), titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb) , Chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), rhodium (Rh), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), zinc (Zn) Boron (B), aluminum (Al), gallium (Ga), indium (In), tin (Sn), lanthanum (La), cerium (Ce), and the like. As M ′, at least one of transition metal elements such as Ni, Fe, Co, and Ti can be preferably used.

  Note that whether or not the compound (oxide) has a spinel structure can be determined by X-ray structural analysis (preferably single crystal X-ray structural analysis). More specifically, it can be determined by measurement using an X-ray diffractometer (for example, “single crystal automatic X-ray structure analyzer” manufactured by Rigaku Corporation) using CuKα rays (wavelength 0.154051 nm).

As a preferable example of the spinel type lithium manganese oxide represented by the general formula (F1), a compound in which M ′ in the general formula (F1) includes at least Ni can be given. Specific examples of such compounds include the following general formula:
_{Li x (Ni t Mn 2-} t-u M "u) O 4 + d (F2);
The spinel type lithium nickel manganese oxide represented by these is mentioned.
Here, M ″ may be any transition metal element or typical metal element other than Ni and Mn (for example, one or more selected from Fe, Ti, Co, Cu, Cr, Zn, and Al). It is preferable to include at least one of trivalent Fe and trivalent Co. Alternatively, part or all of M ″ is a metalloid element (for example, one or more selected from B, Si and Ge). Or a non-metallic element. Also, x may be 0.9 ≦ x ≦ 1.2. t may be 0 <t. u may be 0 ≦ u. Here, t and u may be numbers satisfying t + u <2 (typically t + u ≦ 1). d is a value that satisfies −0.2 ≦ d ≦ 0.2 and satisfies the charge neutrality condition. In one preferred embodiment, t is 0.2 ≦ t ≦ 1.0 (more preferably 0.4 ≦ t ≦ 0.6, more preferably 0.4 ≦ t ≦ 0.55, for example 0.45 ≦ t. ≦ 0.55); u is 0 ≦ u <1.0 (eg, 0 ≦ u ≦ 0.3). Specific examples of the lithium nickel manganese oxide represented by the general formula (F2) include LiNi _0.5 Mn _1.5 O _{4 and the} like.

In a preferred embodiment of the technology disclosed herein, the positive electrode is a spinel-type lithium nickel manganese oxide partially substituted with Fe and Ti (hereinafter sometimes referred to as “FT-LNM spinel”). It has positive electrode active material particles having a basic composition. This FT-LNM spinel can function as a positive electrode active material having an operating potential (vs. Li ^/ Li ⁺ ) of 4.5 V or higher. For example, positive electrode active material particles containing FT-LNM spinel having an operating potential (vs. Li ^/ Li ⁺ ) higher than 4.5 V (further higher than 4.6 V, for example, higher than 4.7 V) are preferable. The upper limit of the operating potential of the FT-LNM spinel is not particularly limited. Usually, however, the FT-LNM spinel has an operating potential (vs. Li ^/ Li ⁺ ) of 7 V or less (typically 6 V or less, for example, 5.5 V or less). Positive electrode active material particles containing are preferred.

The FT-LNM spinel has a composition in which a part of Ni and / or Mn in a spinel type lithium nickel manganese oxide composed of Li, Ni, Mn and oxygen (O) is substituted with Fe and Ti. Such an FT-LNM spinel is a spinel type in which at least a part of transition metal sites (that is, one or both of Ni sites and Mn sites) in the spinel type lithium nickel manganese oxide is occupied by Fe and Ti. It can also be grasped as lithium nickel manganese oxide.
The FT-LNM spinel only needs to contain both Fe and Ti, and the atomic ratio of Fe and Ti is not particularly limited. Usually, an FT-LNM spinel with an atomic ratio of Fe to Ti (Fe: Ti) of 1:10 to 10: 1 is preferred, more preferably 1: 5 to 5: 1 (eg 1: 3 to 3). : 1, typically 1: 2 to 2: 1).

As a suitable example of the FT-LNM spinel in the technology disclosed herein, a spinel type lithium nickel manganese oxide represented by the following general formula (F3) can be given.
Li _x (Ni _α Mn _β M _γ ) O _{4 + d} (F3)
Here, x in the general formula (F3) may satisfy 0.90 ≦ x ≦ 1.2 (for example, 1.0 ≦ x ≦ 1.1). α can be 0 <α ≦ 0.5 (typically 0.3 ≦ α ≦ 0.5, preferably 0.4 ≦ α ≦ 0.5). β is 0 <β ≦ 1.6 (typically 1.3 ≦ β ≦ 1.6, preferably 1.4 ≦ β ≦ 1.6, for example 1.4 ≦ β ≦ 1.5). obtain. M includes at least Fe and Ti, and may be any element (typically a metal element) other than Ni and Mn. γ is 0 <γ ≦ 0.5 (typically 0 <γ ≦ 0.4, preferably 0.005 <γ ≦ 0.3, for example 0.01 <γ ≦ 0.2. , Α + β + γ is 2 or approximately 2 (for example, 1.9 to 2.1), d is −0.2 ≦ d ≦ 0.2 (preferably −0.15 ≦ d ≦ 0.1). The positive electrode active material particles having such a basic composition are preferable because they can realize a more durable nonaqueous electrolyte secondary battery.

The FT-LNM spinel represented by the general formula (F3) may be, for example, a spinel type lithium nickel manganese oxide represented by the following general formula (1).
_{Li x (Ni 0.5-a Fe} P Mn 1.5-b Ti Q M 0 R) O 4 + d (1)
Here, x in the general formula (1) may satisfy 0.90 ≦ x ≦ 1.2 (for example, 1.0 ≦ x ≦ 1.1). a may be 0 ≦ a (typically 0 ≦ a ≦ 0.2, preferably 0 ≦ a ≦ 0.1, such as 0.01 ≦ a ≦ 0.08). b may be −0.1 ≦ b (typically −0.1 ≦ b ≦ 0.2, preferably 0 ≦ b ≦ 0.1, such as 0.01 ≦ b ≦ 0.08). P is 0 <P ≦ 0.1 (typically 0.005 ≦ P ≦ 0.1, preferably 0.01 ≦ P ≦ 0.08, for example 0.02 ≦ P ≦ 0.07). obtain. Q is 0 <Q ≦ 0.1 (typically 0.005 ≦ Q ≦ 0.1, preferably 0.01 ≦ Q ≦ 0.08, for example 0.02 ≦ Q ≦ 0.07). obtain. M ⁰ can be any element (typically a metal element) other than Ni, Mn, Fe, and Ti. R may be 0 ≦ R (typically 0 ≦ R <0.1, preferably 0 ≦ R <0.05, such as 0 ≦ R <0.02). Here, a + b = P + Q + R. d is −0.2 ≦ d ≦ 0.2 (preferably −0.15 ≦ d ≦ 0.1), and is a value determined so as to satisfy the charge neutrality condition. The positive electrode active material particles having such a basic composition are preferable because a more durable nonaqueous electrolyte secondary battery can be realized.

When R in the general formula (1) is larger than 0 (that is, 0 <R), M ⁰ is one selected from any metal element and non-metal element other than Ni, Mn, Fe, and Ti, or There may be two or more. Specific examples of elements that can be selected as M ⁰ include lithium (Li), sodium (Na), magnesium (Mg), calcium (Ca), strontium (Sr), zirconium (Zr), vanadium (V), niobium ( Nb), chromium (Cr), molybdenum (Mo), cobalt (Co), rhodium (Rh), palladium (Pd), platinum (Pt), copper (Cu), zinc (Zn), boron (B), aluminum ( Examples include Al), gallium (Ga), indium (In), tin (Sn), lanthanum (La), and cerium (Ce). Alternatively, it may be an FT-LNM spinel substantially free of M ⁰ (ie, R is 0 or substantially 0).

The FT-LNM spinel represented by the general formula (1) may be, for example, a spinel type lithium nickel manganese oxide represented by the following general formula (2).
Li (Ni _0.5-a Fe _P Mn _1.5-b Ti _Q ) O ₄ (2)
A in the general formula (2) is 0 ≦ a (typically 0 ≦ a ≦ 0.2, preferably 0 ≦ a ≦ 0.1, for example, 0.01 ≦ a ≦ 0.08). obtain. b may be −0.1 ≦ b (typically −0.1 ≦ b ≦ 0.2, preferably 0 ≦ b ≦ 0.1, such as 0.01 ≦ b ≦ 0.08). P may be 0.01 ≦ P ≦ 0.1 (preferably 0.01 ≦ P ≦ 0.08, for example 0.02 ≦ P ≦ 0.07). Q may be 0.01 ≦ Q ≦ 0.1 (preferably 0.01 ≦ Q ≦ 0.08, for example 0.02 ≦ Q ≦ 0.07). Here, a + b = P + Q. The positive electrode active material particles having such a basic composition are preferable because a non-aqueous electrolyte secondary battery having particularly good durability can be realized.

The positive electrode active material particles in the technology disclosed herein may have a basic composition of a lithium transition metal compound other than the spinel structure. The basic composition may be, for example, a positive electrode active material having a composition shown in the following (A) to (C).
(A) An olivine-type lithium transition metal compound (phosphate) represented by the general formula: LiMPO ₄ and having a polyanion. Here, M includes at least one transition metal element such as Mn, Fe, Ni, and Co, and may further include another metal element or a non-metal element. Specific examples include LiMnPO ₄ and LiFePO ₄ .
(B) A olivine fluoride type lithium transition metal compound (phosphate) represented by the general formula: Li ₂ MPO ₄ F. Here, M includes at least one transition metal element such as Mn, Ni, Co, and may further include another metal element or a nonmetal element. Specific examples include LiMnPO ₄ F.
(C) A silicate type lithium transition metal compound represented by the general formula: Li ₂ MSiO ₄ . Here, M includes at least one transition metal element such as Mn, Fe, Ni, and Co, and may further include another metal element or a non-metal element. Specific examples include Li ₂ FeSiO _{4 and the} like.

  The positive electrode active material particles in the technology disclosed herein include a central region having the above basic composition and an outer region that covers the outside of the central region. The outer region does not contain at least one kind of transition metal contained in the basic composition, or is a region where the concentration of the transition metal is lower than the basic composition. In the positive electrode active material particles in which the basic composition contains Mn, the outer region is preferably a region where the concentration of Mn (that is, the mass of Mn contained per unit mass) is lower than at least the basic composition. May be a region that does not substantially contain.

  Note that the fact that the outer region does not contain Mn or that the Mn concentration is lower than that in the central region is, for example, analyzed by comparing the concentration of Mn in the central portion of the positive electrode active material particles with the concentration of Mn on the particle surface. Can be grasped. As an analysis method, depth direction analysis by XPS (X-ray photoelectron spectroscopy) can be preferably employed. More specifically, the Mn concentration at each depth is measured by XPS analysis while digging in the depth direction (center direction of the particles) from the surface of the positive electrode active material particles by sputtering (for example, Ar sputtering). The Mn concentration before sputtering is defined as the Mn concentration on the particle surface, and the Mn concentration in the region where the Mn concentration no longer changes with respect to the depth from the particle surface is defined as the Mn concentration at the center of the particle. In the positive electrode active material particles in which the outer region does not contain Mn or the Mn concentration is lower than that in the central region, typically, the Mn concentration gradually increases as it digs in the depth direction from the particle surface. Then, it becomes constant at a higher Mn concentration than the particle surface.

  The outer region may include a material that functions as an active material. Or the outer area | region which does not function as an active material substantially may be sufficient. For example, it may be an outer region that exhibits lithium ion conductivity but does not substantially occlude lithium ions within itself.

  In the positive electrode active material particles in which the basic composition contains Mn, as a preferable composition of the material constituting the outer region, for example, a composition in which at least a part of Mn is removed from the basic composition (for example, lithium nickel manganese oxide), Examples include a composition in which a part of Mn in the basic composition is replaced with another element. Other materials that can form the outer region include various inorganic materials having lithium ion conductivity (typically, inorganic materials that can function as a solid electrolyte). The outer region may contain one or more of such materials.

The outer region covers at least a part of the outer side of the central region, whereby the portion covered with the outer region can be separated from the surface of the positive electrode active material particles. As a result, the surface potential (vs. Li ^/ Li ⁺ ) of at least a part of the positive electrode active material particles can be made lower than the potential of the central region, so that the transition metal ion trapped in the nonaqueous electrolyte can be captured. An event in which the agent is decomposed at the positive electrode can be suppressed. In order to better exhibit such an oxidative degradation inhibiting effect, 50% by area or more (more preferably 75% by area or more, for example 90% by area or more) of the outer surface of the central region is covered with the outer region. It is preferable. In the positive electrode active material particles according to a preferred embodiment, substantially all (for example, 99% by area or more) of the outer surface of the central region is covered with the outer region.

  The positive electrode active material particles in the technology disclosed herein are not limited to those having a structure in which the outer region constitutes the particle surface (that is, a structure in which the outer region is exposed on the particle surface). It may be a structure in which another material is coated on at least a part of the outside. Even with the positive electrode active material particles having such a structure, the effect of having the outer region outside the central region can be exhibited. In a preferred embodiment, the outer region constitutes the surface of the positive electrode active material particles. Such positive electrode active material particles have good productivity and are advantageous from the viewpoint of capacity density of the positive electrode active material particles.

The thickness of the outer region may be 2 nm to 150 nm, for example, and is usually preferably 5 nm to 50 nm (for example, 5 nm to 20 nm). If the thickness of the outer region is too large, the energy density of the positive electrode active material particles tends to decrease or the resistance of the positive electrode tends to increase.
The ratio of the low Mn region to the entire positive electrode active material particles can be set to 0.01% by volume or more, for example. If the thickness of the low Mn region is too small, the effect of improving the durability of the positive electrode active material particles may be reduced, or the sustainability of the effect may be reduced. From this viewpoint, the ratio of the low Mn region to the entire positive electrode active material particles can be, for example, 0.1% by volume or more, and usually 0.2% by volume or more (for example, 0.5% by volume or more) It is appropriate to do. In a preferred embodiment, from the viewpoint of better exhibiting the effect of having a low Mn region, the above ratio may be 1.0 volume or more, and may be 3.0 volume% or more. On the other hand, from the viewpoint of energy density, output characteristics, etc., the proportion of the low Mn region in the whole positive electrode active material particles is usually suitably 20% by volume or less, preferably 15% by volume or less, more preferably May be 10 volume% or less (for example, 5 mass% or less). In another preferred embodiment, from the viewpoint of placing more emphasis on output characteristics, the above ratio can be set to 3.0% by volume or less, or 2.0% by volume or less, and further 1.0% by volume or less ( For example, it is good also as 0.5 volume% or less.

In a preferred embodiment of the technology disclosed herein, the average particle diameter of the positive electrode active material particles may be about 2 μm to 20 μm (for example, about 3 μm to 15 μm). In another preferred embodiment, the average particle diameter of the positive electrode active material particles can be about 5 μm to 30 μm (typically 5 μm to 20 μm, for example, 10 μm to 20 μm). BET specific surface area of the positive electrode active material particle is usually suitably about 0.1~3.0m ² / g, may be used for example 0.2~1.0m preferably of about ² / g.

<Method for producing positive electrode active material particles>
The manufacturing method of the positive electrode active material particle disclosed here is not particularly limited. For example, a production method (surface coating method) including preparing raw material particles having the above basic composition and coating at least a part of the raw material particles with an outer region is exemplified.
Hereinafter, in the case where the basic composition is FT-LMN spinel and the outer region is a region having a lower Mn concentration than the basic composition, the production of positive electrode active material particles by the surface coating method will be more detailed. This will be specifically described. In the following description, a region having a lower Mn concentration than the basic composition (which may be a region that does not substantially contain Mn) may be referred to as a “low Mn region”.

  As raw material particles having a basic composition of FT-LNM spinel (hereinafter also referred to as “FT-LNM raw material particles”), those produced by a known method can be used. The FT-LNM raw material particles may be particles substantially composed of FT-LNM spinel. As a raw material for obtaining FT-LNM raw material particles, a suitable Li source (a compound containing Li or Li. For example, lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, etc.), a Mn source (a compound containing Mn or Mn) For example, manganese dioxide, manganese carbonate, etc.), Ni source (Ni or Ni-containing compound, such as nickel hydroxide), Fe source (Fe or Fe-containing compound), Ti source (Ti or Ti-containing compound), etc. are used. be able to. In a preferred embodiment, such a Li source, Mn source, Ni source, Fe source, Ti source, and other materials used as necessary depending on the composition of the target product (that is, target FT-LNM raw material particles). A metal source is mixed in a ratio corresponding to the composition of the target product, and the mixture is fired in an oxidizing atmosphere. FT-LNM raw material particles having desired properties can be prepared by applying a treatment such as crushing and sieving to the fired product as necessary.

The properties of the FT-LNM raw material particles can be appropriately selected in consideration of the method for forming the low Mn region, the properties of the target positive electrode active material particles, and the like. In a preferred embodiment, FT-LNM raw material particles having an average particle diameter of about 2 μm to 20 μm (for example, about 3 μm to 15 μm) can be preferably used. In another preferred embodiment, FT-LNM raw material particles having an average particle diameter of 5 μm to 30 μm (typically 5 μm to 20 μm, for example, 10 μm to 20 μm) can be preferably used. BET specific surface area of the FT-LNM material particles is usually suitably about 0.1~3.0m ² / g, may be used for example 0.2~1.0m preferably of about ² / g.

The low Mn region (outer region) formed outside the FT-LNM raw material particles is preferably a solid layer having Li ion conductivity. As a suitable composition of such a low Mn region, an inorganic compound containing lithium, for example, Li ₃ PO ₄ , Li ₄ P ₂ O ₇ , LiPO ₃ , LiI, LiN, Li ₂ O, Li ₂ O ₂ , LiF, etc. Or the composition containing 2 or more types is illustrated. Other preferred examples include compositions containing various inorganic solid electrolytes (such as lithium ion conductive glass ceramics) that are known to be capable of functioning as electrolytes for all solid-state lithium ion secondary batteries and the like.

In a preferred embodiment, the low Mn region is configured as a coating layer containing a lithium phosphate compound such as Li ₃ PO ₄ , Li ₄ P ₂ O ₇ , LiPO ₃ or the like. Such a coating layer is obtained by, for example, attaching a precursor capable of forming a lithium phosphate compound to the surface of FT-LNM raw material particles by heating, and firing the precursor-equipped FT-LNM raw material particles under appropriate conditions. More preferably. The precursor can be prepared, for example, by drying an aqueous solution containing LiNO ₃ and (NH ₄ ) ₂ HPO ₄ . As a method of attaching the precursor to the surface of the FT-LNM raw material particles, a method of mechanically mixing them can be preferably employed. The firing is preferably performed in an oxidizing atmosphere (for example, an air atmosphere). The firing temperature is not particularly limited, but it is usually appropriate to set the firing temperature to about 300 ° C to 500 ° C. The firing time can be, for example, about 30 minutes to 24 hours, and is usually about 1 hour to 12 hours. Another method for forming the coating layer is, for example, a method in which the powder of the lithium phosphate compound is attached to the surface of the FT-LNM raw material particles and calcined under appropriate conditions.

<Positive electrode sheet>
The positive electrode in the technology disclosed herein is configured to include the positive electrode active material particles as described above. Therefore, the positive electrode contains at least a lithium transition metal compound constituting the central region of the positive electrode active material particles as described above as the positive electrode active material. The lithium transition metal compound is a lithium transition metal compound having an operating potential (vs. Li ^/ Li ⁺ ) higher than 4.5 V. For example, the general formula (F1), the general formula (F2), and the general formula (F3) ), A lithium transition metal compound represented by the general formula (1) or the general formula (2).

  The positive electrode which concerns on a preferable one aspect | mode includes the positive electrode active material layer containing the said positive electrode active material particle, and the positive electrode collector which supports the positive electrode active material layer. As the positive electrode current collector, a conductive member made of a metal having good conductivity (for example, aluminum, nickel, titanium, stainless steel, etc.) is preferably used. The shape of the current collector is not particularly limited because it may vary depending on the shape of the battery to be constructed, and may be, for example, a bar shape, a plate shape, a foil shape, a net shape, or the like. In a battery provided with a wound electrode body, a foil-shaped (sheet-shaped) current collector is preferably used. The thickness of the sheet current collector is not particularly limited. In view of the balance between the capacity density of the battery and the strength of the current collector, a sheet-like current collector (eg, aluminum foil) of about 5 μm to 50 μm (more preferably 8 μm to 30 μm) can be preferably used.

  Such a positive electrode includes a paste-like or slurry-like composition (dispersion for forming a positive electrode active material layer) in which the positive electrode active material particles and a conductive material or a binder used as necessary are dispersed in an appropriate solvent. The liquid can also be preferably prepared by applying a “positive electrode active material layer forming composition”) to a sheet-like positive electrode current collector and drying the composition. As the solvent, any of an aqueous solvent and an organic solvent can be used. For example, N-methyl-2-pyrrolidone (NMP) can be used.

  As the conductive material, for example, a carbon material can be used. More specifically, for example, various carbon blacks (for example, acetylene black, furnace black, ketjen black, channel black, lamp black, thermal black), coke, activated carbon, graphite (natural graphite, artificial graphite), carbon fiber One or more selected from carbon materials such as (PAN-based carbon fiber, pitch-based carbon fiber), carbon nanotube, fullerene, and graphene can be preferably used. Among them, it is preferable to use carbon black (typically acetylene black) having a relatively small particle size and a large specific surface area.

  As the binder, a polymer that can be dissolved or dispersed in a solvent to be used can be used. For example, in the composition for forming a positive electrode active material layer using an aqueous solvent, cellulose-based polymers such as carboxymethyl cellulose (CMC; typically sodium salt), hydroxypropylmethyl cellulose (HPMC); polyvinyl alcohol (PVA); Fluorine resins such as tetrafluoroethylene (PTFE); rubbers such as styrene butadiene rubber (SBR) can be preferably used. In the composition for forming a positive electrode active material layer using a nonaqueous solvent, polyvinylidene fluoride (PVdF), polyvinylidene chloride (PVdC), or the like can be preferably used. In addition, the polymer which melt | dissolves in the solvent to be used can also be grasped | ascertained as a thickener of the composition for positive electrode active material layer forming.

  The proportion of the positive electrode active material particles in the entire positive electrode active material layer is suitably about 50% by mass or more (typically 50% by mass to 95% by mass), and usually about 70% by mass to 95%. It is preferable that it is mass%. When the conductive material is used, the ratio of the conductive material in the entire positive electrode active material layer can be, for example, approximately 2% by mass to 20% by mass, and is generally preferably approximately 2% by mass to 15% by mass. . When using a binder, the ratio of the binder to the whole positive electrode active material layer can be, for example, about 0.5 mass% to 10 mass%, and is usually about 1 mass% to 7 mass% (for example, about 1 mass). % To 5% by mass).

The positive electrode active material layer is made of a material that can function as the positive electrode active material of the nonaqueous electrolyte secondary battery in a form different from the positive electrode active material particles disclosed herein, as long as the effect of the present invention is not significantly reduced. Further, it can be contained. Such a material can be, for example, a lithium transition metal oxide having a known layered structure or spinel structure, a polyanion type (for example, olivine type) lithium transition metal compound, and the like. The upper limit operating potential (vs. Li ^/ Li ⁺ ) of the positive electrode active material contained in a form different from the positive electrode active material particles may be less than 4.5 V (for example, 4.0 to 4.2 V). 4.5V or more. For example, in addition to the positive electrode active material particles disclosed herein, the positive electrode active material layer may include FT-LNM spinel particles (typically particles made of FT-LNM spinel) having no outer region. . The amount of the positive electrode active material contained in a form different from the positive electrode active material particles can be 25% by mass or less of the entire positive electrode active material layer, and is usually 15% by mass or less, preferably It is 10 mass% or less (for example, 5 mass% or less). It may be a positive electrode active material layer substantially free of such a positive electrode active material.

The mass of the positive electrode active material layer provided per unit area of the positive electrode current collector (the total mass on both sides in the configuration having the positive electrode active material layer on both surfaces of the positive electrode current collector) is, for example, 5 mg / cm ^{2 to} 40 mg / cm ^2. (typically ^{10mg / cm 2 ~20mg / cm 2} ) it is appropriate to the degree. In the configuration having the positive electrode active material layers on both surfaces of the positive electrode current collector, the mass of the positive electrode active material layers provided on each surface of the positive electrode current collector is usually preferably approximately the same. Further, the density of the positive electrode active material layer can be, for example, about 1.5 g / cm ^{3 to} 4 g / cm ³ (typically 1.8 g / cm ^{3 to 3} g / cm ³ ). By setting the density of the positive electrode active material layer in the above range, the diffusion resistance of lithium ions can be kept low while maintaining a desired capacity. For this reason, the output characteristics and energy density of the nonaqueous electrolyte secondary battery can be made compatible at a higher level.

<Negative electrode>
The negative electrode of the nonaqueous electrolyte secondary battery disclosed herein is typically configured to include a suitable negative electrode active material. The negative electrode which concerns on one preferable aspect contains the negative electrode active material layer containing the said negative electrode active material, and the negative electrode collector which supports the negative electrode active material layer. As the negative electrode current collector, a conductive material made of a metal having good conductivity (for example, copper, nickel, titanium, stainless steel, etc.) is preferably used. The shape of the negative electrode current collector can be the same as that of the positive electrode current collector. In a battery provided with a wound electrode body, a foil-shaped (sheet-shaped) current collector is preferably used. For example, a sheet-like current collector (for example, copper foil) having a thickness of about 5 μm to 50 μm (more preferably 8 μm to 30 μm) can be preferably used.

  Such a negative electrode includes a paste-like or slurry-like composition (a dispersion for forming a negative electrode active material layer) in which a negative electrode active material and a binder (binder) used as necessary are dispersed in a suitable solvent. (Hereinafter also referred to as “negative electrode active material layer forming composition”) is applied to a sheet-like negative electrode current collector, and the composition is dried to form a negative electrode active material layer (negative electrode active material layer). Preferably it can be produced. As the solvent, any of an aqueous solvent and an organic solvent can be used. For example, water can be used.

As the negative electrode active material, one type or two or more types of materials conventionally used in non-aqueous electrolyte secondary batteries can be used without particular limitation. For example, carbon materials such as natural graphite (graphite), artificial graphite, hard carbon (non-graphitizable carbon), soft carbon (graphitizable carbon), carbon nanotubes; silicon oxide, titanium oxide, vanadium oxide, iron oxide, cobalt oxide , Nickel oxide, niobium oxide, tin oxide, lithium silicon oxide, lithium titanium oxide (Lithium Titanium Composite Oxide: LTO, for example, Li ₄ Ti ₅ O ₁₂ , LiTi ₂ O ₄ , Li ₂ Ti ₃ O ₇ ), lithium vanadium Metal oxide materials such as oxide, lithium manganese oxide, lithium tin oxide; metal nitride materials such as lithium nitride, lithium cobalt composite nitride, lithium nickel composite nitride; tin, silicon, aluminum, zinc, lithium, etc. Metal materials made of metals or metal alloys mainly composed of these metal elements; etc. It can be used.

As the negative electrode active material in the technology disclosed herein, the reduction potential (vs. Li ^/ Li ⁺ ) is about 0.5 V or less from the viewpoint that a non-aqueous electrolyte secondary battery having a higher energy density can be realized. More preferably, a negative electrode active material of 0.2 V or less (for example, 0.1 V or less) can be preferably used. Examples of such a material that can be a low potential include a carbon material having a graphite structure at least partially. Preferable examples include graphite-based graphite particles such as natural graphite and artificial graphite. Other preferred examples include carbon particles in a form in which such graphite particles are coated (coated) with an amorphous carbon material. Since the surface of such carbon particles is coated with an amorphous carbon material, the reactivity with the non-aqueous electrolyte is kept relatively low. Therefore, in the nonaqueous electrolyte secondary battery using such particles as the negative electrode active material, the irreversible capacity is suppressed and high durability can be exhibited.

The shape of the negative electrode active material is usually preferably in the form of particles having an average particle diameter of 1 μm to 50 μm (typically 3 μm to 30 μm, for example, 10 μm to 25 μm). BET specific surface area of the negative electrode active material, ^typically, 0.1m ² / ^g~30m 2 / g approximately are suitable, typically 0.5m ² / g~10m ² / g, preferably from ^{1 m} 2 / g ~5m is ² / g (e.g. ^{2m 2} / ^g~3m 2 / g) approximately. When the property of the negative electrode active material is in the above range, the reductive decomposition of the nonaqueous electrolyte can be suitably suppressed. Moreover, since an appropriate space | gap can be hold | maintained in this negative electrode active material layer, there exists an advantage that a nonaqueous electrolyte is easy to be immersed and internal resistance is easy to reduce.

  As the binder, an appropriate material can be selected from the polymer materials exemplified as the binder for the positive electrode active material layer. Specific examples include styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), CMC, and the like. In addition, various additives such as a dispersant and a conductive material can be used as appropriate.

  The proportion of the negative electrode active material in the entire negative electrode active material layer is suitably about 50% by mass or more, and preferably 90% by mass to 99.5% by mass (eg, 95% by mass to 99% by mass). . When using a binder, the ratio of the binder to the whole negative electrode active material layer can be, for example, about 0.5 mass% to 10 mass%, and usually about 1 mass% to 5 mass%. Is appropriate.

The mass of the negative electrode active material layer provided per unit area of the negative electrode current collector (the total mass of both surfaces in the case of having a negative electrode active material layer on both surfaces of the negative electrode current collector) is, for example, 5 mg / cm ^{2 to} 20 mg / cm ^2. (typically ^{5mg / cm 2 ~10mg / cm 2} ) it is appropriate to the degree. In the configuration having the negative electrode active material layers on both surfaces of the negative electrode current collector, the mass of the negative electrode active material layers provided on each surface of the negative electrode current collector is usually preferably approximately the same. The density of the negative electrode active material layer, for example, (typically ^{1g / cm 3 ~1.5g / cm 3} ) 0.5g / cm 3 ~2g / cm 3 may be of the order. By setting the density of the negative electrode active material layer in the above range, the interface with the non-aqueous electrolyte can be suitably maintained, and both durability (cycle characteristics) and output characteristics can be achieved at a high level.

<Electrode body>
The positive electrode and negative electrode prepared above are laminated to produce an electrode body. In a typical configuration of the nonaqueous electrolyte secondary battery disclosed herein, a separator is interposed between the positive electrode and the negative electrode. As this separator, the same separator as that for a general non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) can be used without particular limitation. For example, a porous sheet made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide, a nonwoven fabric, or the like can be used. Preferable examples include a porous sheet (microporous resin sheet) having a single-layer or multilayer structure mainly composed of one or more polyolefin resins. For example, a PE sheet, a PP sheet, a sheet having a three-layer structure (PP / PE / PP structure) in which PP layers are laminated on both sides of the PE layer, and the like can be suitably used. The thickness of the separator is preferably set within a range of approximately 10 μm to 40 μm, for example.

<Capacitance ratio between positive electrode and negative electrode>
Although not particularly limited, the positive electrode capacity (C _c (mAh)) calculated by the product of the theoretical capacity (mAh / g) per unit mass of the positive electrode active material and the mass (g) of the positive electrode active material. And the negative electrode capacity (C _a (mAh)) calculated by the product of the theoretical capacity per unit mass of the negative electrode active material (mAh / g) and the mass of the negative electrode active material (g) (C _a / C _c ) is usually suitably 1.0 to 2.0, for example, and preferably 1.2 to 1.9 (eg 1.3 to 1.8). The ratio of the positive electrode capacity and the negative electrode capacity facing each other directly affects the battery capacity (or irreversible capacity) and the energy density, and lithium is likely to be precipitated depending on the use conditions of the battery (for example, rapid charging). By setting the capacity ratio of the opposing positive and negative electrodes in the above range, it is possible to favorably suppress lithium deposition while maintaining good battery characteristics such as battery capacity and energy density.

<Nonaqueous electrolyte>
The nonaqueous electrolyte in the technology disclosed herein is characterized by including a transition metal ion scavenger. As the transition metal ion scavenger, various compounds capable of trapping transition metal ions (typically transition metal ions eluted from the positive electrode active material, such as Mn ions) to be captured can be used. For example, a compound capable of forming a complex by binding to the transition metal ion (which may be a coordination bond) can be preferably employed as the transition metal ion scavenger. Hereinafter, a compound that can be combined with the transition metal ion to form a complex may be referred to as a “complex-forming compound”.

Examples of the complex-forming compound include acetylacetone, benzoyltrifluoroacetone, dipivaloylmethane, furoyltrifluoroacetone, hexafluoroacetylacetone, heptafluorobutanoylpivaloylmethane, 3-phenylacetylacetone, and pivaloyltrifluoro. Β-diketones such as acetone, trifluoroacetylacetone, and tenoyltrifluoroacetone; ethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, tetraethylenepentamine, pentaethylenehexamine, tris (2-aminoethyl) amine Polyamines such as 2,2-dipyridyl, 1,10-phenanthroline and the like; 12-crown-4-ether, 15-crown-5-ether, benzo-15-kura It can be preferably employed and the like; down-5-ether, N- phenylazo-15-crown-5-ether, crown ethers such as 18-crown-6-ether. Other examples include oximes such as phenyl-2-pyridylketoxime; azo compounds such as 1- (2-thiazolylazo) -2-naphthol and 1- (2-pyridylazo) -2-naphthol; other N-nitrosodiethylamine 2,3-dimercapto-1-propanol and the like. Alternatively, an ammonium salt such as ammonium iodide (NH ₄ I) may be used as the complex-forming compound. Such complex-forming compounds can be used singly or in appropriate combination of two or more. For example, a compound capable of forming a chelate complex with the transition metal ion (chelate-forming compound) can be preferably employed. A compound that can be dissolved or dispersed in a nonaqueous solvent contained in the nonaqueous electrolyte can be preferably used.

  Preferred examples of the transition metal ion scavenger in the technology disclosed herein include acetylacetone, ethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, tetraethylenepentamine, pentaethylenehexamine, tris (2-aminoethyl). ) Complexing compounds such as amines, 2,2-dipyridyl, 1,10-phenanthroline, N-nitrosodiethylamine, 2,3-dimercapto-1-propanol and ammonium iodide. In one preferred embodiment, one or more selected from these complex-forming compounds are used. Such a complex-forming compound is preferable because it can form a stable metal complex (for example, Mn complex). A particularly preferred transition metal ion scavenger is acetylacetone.

Such a compound that functions as a transition metal ion scavenger is generally a compound that includes a moiety that exhibits an affinity for the transition metal ion (cation) that is to be captured. Thus, the part (electron-donating functional group or the like) showing affinity for the cation tends to be easily subjected to oxidative decomposition at the positive electrode. In a nonaqueous electrolyte secondary battery having a high positive electrode operating potential (eg, 4.5 V (vs. Li ^/ Li ⁺ ) or more), oxidative decomposition of the transition metal ion scavenger is particularly likely to occur. When the transition metal ion scavenger in the non-aqueous electrolyte is oxidatively decomposed, the degradation product may form a film on the positive electrode, and the battery performance may be deteriorated. This is because in a conventional non-aqueous electrolyte secondary battery using a spinel type lithium nickel manganese oxide, the capacity deterioration due to charging / discharging has become remarkable by containing a chelating agent or the like in the non-aqueous electrolyte. It is thought to be a cause.

  According to the technology disclosed herein, the positive electrode active material particles have an outer region that covers the central region, whereby the potential of the surface of the positive electrode active material particles can be made lower than that of the central region. The transition metal ion scavenger contained in can be prevented from being decomposed at the positive electrode. Therefore, it is possible to avoid the deterioration of the battery performance due to the decomposition of the transition metal ion scavenger and to trap the transition metal eluted from the positive electrode with the transition metal ion scavenger. Thereby, precipitation of the eluted transition metal on the negative electrode is prevented, and the durability of the battery can be effectively improved. The trapped transition metal ion is preferably in a state contained in the non-aqueous electrolyte (for example, a state in which the transition metal ion is dissolved or dispersed in the non-aqueous electrolyte as a complex of a transition metal ion scavenger and a transition metal ion). Maintained.

In consideration of the composition of the positive electrode active material, the type of the transition metal ion scavenger, the usage mode planned for the non-aqueous electrolyte secondary battery, the required degree of durability, etc. It can be set appropriately. For example, in the nonaqueous electrolyte secondary battery having a form as shown in FIGS. 1 to 3 described later, the concentration of the transition metal ion scavenger contained in the nonaqueous electrolyte is, for example, from the viewpoint of the trapping efficiency of transition metal ions, It can be greater than 0.001 mol / L, and it is usually appropriate to be greater than 0.005 mol / L (preferably greater than 0.01 mol / L). Also, from the viewpoint of cost and the solubility and dispersibility of the transition metal ion scavenger, the concentration of the transition metal ion scavenger is usually suitably less than 5 mol / L, and less than 1 mol / L ( For example, it is preferably less than 0.5 mol / L. The nonaqueous electrolyte which concerns on a preferable one aspect | mode contains a transition metal ion scavenger in the density | concentration of 0.12 mol / L or more and 0.4 mol / L or less.
When acetylacetone is used as the transition metal ion scavenger, a nonaqueous electrolyte containing acetylacetone at a concentration higher than 0.5% by mass and lower than 5% by mass (for example, a concentration higher than 1% by mass and lower than 3% by mass) is preferable. Can be used.

  As the nonaqueous electrolyte in the technology disclosed herein, an electrolytic solution containing the transition metal ion scavenger as described above, a nonaqueous solvent, and a supporting salt (supporting electrolyte) can be preferably used.

As the supporting salt, those similar to the supporting salt that can be used in a general nonaqueous electrolyte secondary battery can be appropriately selected and used. Examples of such supporting salts include lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO ₃ . Such a supporting salt can be used singly or in combination of two or more. LiPF ₆ may be mentioned as particularly preferred support salt. Moreover, it is preferable to prepare electrolyte solution so that the density | concentration of the said support salt may exist in the range of 0.7 mol / L-1.3 mol / L, for example.
The technology disclosed herein can be preferably applied to a non-aqueous electrolyte secondary battery including an electrolytic solution containing a lithium salt containing fluorine as a supporting salt. The electrolytic solution having such a composition can be oxidized and decomposed at the positive electrode to generate an acid such as hydrogen fluoride (HF). By this acid, elution of the transition metal element (for example, Mn) contained in the positive electrode active material can be accelerated. Therefore, in a non-aqueous electrolyte secondary battery including an electrolytic solution containing a lithium salt containing fluorine as a supporting salt, it is particularly preferable to apply the technology disclosed herein to suppress elution of transition metal from the positive electrode active material. It is meaningful.

  Examples of the non-aqueous solvent include organic solvents such as various carbonates, ethers, esters, nitriles, sulfones, and lactones that are used in an electrolyte solution of a general non-aqueous electrolyte secondary battery. Can be used. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), 1,2-dimethoxyethane, , 2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ -Butyrolactone and the like are exemplified. The carbonates mean to include cyclic carbonates and chain carbonates, and the ethers mean to include cyclic ethers and chain ethers. Such a non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types as appropriate.

  In the electrolytic solution according to a preferred embodiment, the non-aqueous solvent is a non-aqueous solvent mainly composed of carbonates. As carbonates, EC having a high relative dielectric constant, DMC, EMC, etc. having a high oxidation potential (wide potential window) can be preferably used. For example, one or more carbonates are included as the non-aqueous solvent, and the total volume of these carbonates is 60% by volume or more (more preferably 75% by volume or more, more preferably 90% by volume) of the total volume of the non-aqueous solvent. % Or more and may be substantially 100% by volume).

The oxidation potential (vs. Li ^/ Li ⁺ ) of the electrolytic solution is desirably equal to or higher than the operating potential (vs. Li ^/ Li ⁺ ) of the positive electrode active material. For example, the difference from the operating potential (vs. Li ^/ Li ⁺ ) of the positive electrode active material is larger than 0 V (typically about 0.1 V to 3.0 V, preferably about 0.2 V to 2.0 V, for example, 0 An electrolytic solution of about 3 V to 1.0 V) can be preferably used.

The oxidation potential (vs. Li ^/ Li ⁺ ) of the electrolytic solution can be measured by the following method. First, a working electrode (WE) is produced using LiNi _0.5 Mn _1.5 O ₄ . A tripolar cell is constructed using the WE, metallic lithium as a counter electrode (CE), metallic lithium as a reference electrode (RE), and an electrolyte to be measured. The triode cell is completely desorbed from WE. Specifically, at a temperature of 25 ° C., constant current charging is performed up to 4.2 V with a current value of 1/5 of the battery capacity (Ah) predicted from the theoretical capacity of the WE, and at 4.2 V, the current value is the initial current. The constant voltage charging is performed until it becomes 1/50 of the value (that is, the current value of 1/5 of the battery capacity). Next, constant voltage charging for a predetermined time (for example, 10 hours) is performed at an arbitrary voltage in a voltage range (typically a voltage range higher than 4.2 V) predicted to include the oxidation potential of the electrolyte to be measured. And measure the current value. More specifically, the voltage is increased stepwise (for example, in steps of 0.2 V) within the above voltage range, and constant voltage charging is performed for a predetermined time (for example, about 10 hours) at each step. Measure the current value. The potential when the current value during constant voltage charging is greater than 0.1 mA is defined as the oxidation potential (oxidation decomposition potential) of the electrolytic solution.

<Fluorine-containing non-aqueous solvent>
In a preferred embodiment of the technology disclosed herein, the nonaqueous electrolyte contains a fluorine-containing nonaqueous solvent. A non-aqueous electrolyte having such a composition (which may be a non-aqueous electrolyte containing a fluorine-containing lithium salt and a fluorine-containing non-aqueous solvent) has high resistance to oxidative decomposition and high positive electrode operating potential (vs. Li / Li +). While suitable as a non-aqueous electrolyte constituent of a secondary battery, hydrogen fluoride (HF) is likely to be produced when the fluorine-containing non-aqueous solvent is oxidatively decomposed. This hydrogen fluoride can be a factor that accelerates elution of a transition metal element (for example, Mn) contained in the positive electrode active material. Therefore, it is particularly meaningful to suppress the elution by applying the technology disclosed herein.

  The fluorine-containing non-aqueous solvent may be, for example, a fluorinated product of an organic solvent (organic compound) that is known to be used for an electrolyte solution of a non-aqueous electrolyte secondary battery. In other words, it may be an organic solvent having a chemical structure in which at least one hydrogen atom of an organic solvent not containing fluorine as a constituent element is substituted with a fluorine atom. The “non-aqueous solvent containing no fluorine as a constituent element” may be various carbonates, ethers, esters, nitriles, sulfones, lactones and the like. The carbonates mean to include cyclic carbonates and chain carbonates, and the ethers mean to include cyclic ethers and chain ethers. Such fluorine-containing non-aqueous solvents can be used singly or in appropriate combination of two or more.

  The degree of fluorination in the fluorine-containing non-aqueous solvent is usually suitably 10% or more, preferably 20% or more, more preferably 30% or more (for example, 40% or more). Here, the “degree of fluorination” refers to a ratio of [(number of fluorine atoms of fluorine-containing nonaqueous solvent) / (number of hydrogen atoms of corresponding non-fluorine-containing nonaqueous solvent)] (hereinafter, This is also referred to as “fluorine substitution rate”). The upper limit of the fluorine substitution rate is not particularly defined, and may be 100% (that is, a compound in which all of the hydrogen atoms are replaced with fluorine atoms). Further, from the viewpoint of lowering the viscosity of the electrolyte, improving ion conductivity, etc., a fluorine-containing nonaqueous solvent having a fluorine substitution rate of 90% or less (typically 80% or less, for example 70% or less) can be preferably used. .

<Fluorinated carbonate>
The non-aqueous electrolyte which concerns on preferable one aspect | mode is 1 type, or 2 or more types of fluorinated carbonate (Any of a fluorinated cyclic carbonate and a fluorinated chain carbonate can be used preferably) as said fluorine-containing non-aqueous solvent. Containing. Usually, it is preferable to use a fluorinated carbonate having one carbonate structure in one molecule. The fluorine substitution rate of such a fluorinated carbonate is usually suitably 10% or more, for example, 20% or more (typically 20% or more and 100% or less, eg 20% or more and 80% or less). According to an electrolytic solution containing a fluorinated carbonate having a fluorine substitution rate of 30% or more (typically 30% or more and 100% or less, for example, 30% or more and 70% or less), a higher oxidation potential (high oxidation resistance) is realized. obtain.

<Fluorinated cyclic carbonate>
As a suitable example of the nonaqueous electrolyte in the technique disclosed here, an electrolytic solution having a composition containing at least one fluorinated cyclic carbonate as the fluorine-containing nonaqueous solvent may be mentioned. Of all the components excluding the supporting salt from the electrolytic solution (hereinafter also referred to as “component other than the supporting salt”), the amount of the fluorinated cyclic carbonate can be, for example, 5% by mass or more, and usually 10% by mass. % Or more is suitable, and 20% by mass or more (for example, 30% by mass or more) is preferable. Substantially 100% by mass (typically 99% by mass or more) of the components other than the supporting salt may be a fluorinated cyclic carbonate. Usually, from the viewpoint of lowering the viscosity of the electrolyte, improving ion conductivity, etc., it is appropriate that the amount of the fluorinated cyclic carbonate in the components other than the supporting salt is 90% by mass or less, and 80% by mass or less. (For example, 70% by mass or less) is preferable. In addition, when the said electrolyte solution contains 2 or more types of fluorinated cyclic carbonates, the quantity of the said fluorinated cyclic carbonate points out those total amount.

  The fluorinated cyclic carbonate is preferably one having 2 to 8 carbon atoms (more preferably 2 to 6, for example 2 to 4, typically 2 or 3). When there are too many carbon atoms, the viscosity of electrolyte solution may become high or ion conductivity may fall. For example, a fluorine-containing carbonate represented by the following formula (C1) can be preferably used.

R ¹¹ , R ¹² and R ¹³ in the above formula (C1) are each independently a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 4 (more preferably 1 or 2, typically 1) carbon atoms. And haloalkyl groups, and halogen atoms other than fluorine (preferably chlorine atoms). The haloalkyl group may be a group having a structure in which one or more hydrogen atoms of the alkyl group are substituted with a halogen atom (for example, a fluorine atom or a chlorine atom, preferably a fluorine atom). A compound in which one or two of R ¹¹ , R ¹² and R ¹³ are fluorine atoms is preferred. For example, a compound in which at least one of R ¹² and R ¹³ is a fluorine atom is preferable. From the viewpoint of reducing the viscosity of the electrolytic solution, a compound in which R ¹¹ , R ¹² and R ¹³ are all fluorine atoms or hydrogen atoms can be preferably employed.

  Specific examples of the fluorinated cyclic carbonate represented by the above formula (C1) include monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), 4,4-difluoroethylene carbonate, trifluoroethylene carbonate, perfluoroethylene. Carbonate, 4-fluoro-4-methylethylene carbonate, 4,5-difluoro-4-methylethylene carbonate, 4-fluoro-5-methylethylene carbonate, 4,4-difluoro-5-methylethylene carbonate, 4- (fluoro Methyl) -ethylene carbonate, 4- (difluoromethyl) -ethylene carbonate, 4- (trifluoromethyl) -ethylene carbonate, 4- (fluoromethyl) -4-fluoroethylene carbonate, -(Fluoromethyl) -5-fluoroethylene carbonate, 4-fluoro-4,5-dimethylethylene carbonate, 4,5-difluoro-4,5-dimethylethylene carbonate, 4,4-difluoro-5,5-dimethylethylene carbonate, etc. Is mentioned. As difluoroethylene carbonate, any of trans-difluoroethylene carbonate (trans-DFEC) and cis-difluoroethylene carbonate (cis-DFEC) can be used. Usually, the use of trans-DFEC is more preferable. Since trans-DFEC exhibits a liquid state at normal temperature (for example, 25 ° C.), there is an advantage that it is superior in handling property compared to solid cis-DFEC at normal temperature.

<Fluorinated chain carbonate>
The non-aqueous electrolyte in the technique disclosed here is, for example, the following formula (C2), instead of or in addition to the fluorinated cyclic carbonate as described above, as the fluorine-containing non-aqueous solvent. The fluorine chain carbonate represented by these can be used.

At least one (preferably both) of R ²¹ and R ²² in the formula (C2) is an organic group containing fluorine, and may be, for example, a fluorinated alkyl group or a fluorinated alkyl ether group. It may be a fluorinated alkyl group or a fluorinated alkyl ether group further substituted with a halogen atom other than fluorine. One of R ²¹ and R ²² may be an organic group that does not contain fluorine (for example, an alkyl group or an alkyl ether group). Each of R ²¹ and R ²² is preferably an organic group having 1 to 6 carbon atoms (more preferably 1 to 4, for example 1 to 3, typically 1 or 2). When there are too many carbon atoms, the viscosity of electrolyte solution may become high or ion conductivity may fall. For the same reason, usually, it is preferable that at least one of R ²¹ and R ²² is linear, more preferably R ²¹ and R ²² are both linear. For example, a fluorine chain carbonate in which R ²¹ and R ²² are both fluorinated alkyl groups and the total number of carbon atoms thereof is 1 or 2 can be preferably used.

  Specific examples of the fluorinated chain carbonate represented by the above formula (C2) include fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate, fluoromethyl difluoromethyl carbonate (hereinafter referred to as “TFDMC”). ), Bis (fluoromethyl) carbonate, bis (difluoromethyl) carbonate, bis (trifluoromethyl) carbonate, (2-fluoroethyl) methyl carbonate, ethylfluoromethyl carbonate, (2,2-difluoroethyl) methyl carbonate , (2-fluoroethyl) fluoromethyl carbonate, ethyl difluoromethyl carbonate, (2,2,2-trifluoroethyl) methyl carbonate, (2,2-difluoroethyl) ) Fluoromethyl carbonate, (2-fluoroethyl) difluoromethyl carbonate, ethyl trifluoromethyl carbonate, ethyl- (2-fluoroethyl) carbonate, ethyl- (2,2-difluoroethyl) carbonate, bis (2-fluoroethyl) Carbonate, ethyl- (2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl-2′-fluoroethyl carbonate, bis (2,2-difluoroethyl) carbonate, 2,2,2-trifluoro Ethyl-2′-fluoroethyl carbonate, 2,2,2-trifluoroethyl-2 ′, 2′-difluoroethyl carbonate, bis (2,2,2-trifluoroethyl) carbonate, pentafluoroethyl methyl carbonate, penta Fluoroe Le fluoromethyl carbonate, pentafluoroethyl ethyl carbonate, bis (pentafluoroethyl) carbonate.

  The electrolytic solution according to a preferred embodiment contains at least one fluorinated cyclic carbonate and at least one fluorinated chain carbonate as the fluorine-containing nonaqueous solvent. In the electrolytic solution having such a composition, the fluorinated chain carbonate (preferably, fluorinated linear carbonate) is used to make the electrolytic solution liquid at room temperature (for example, 25 ° C.) or to reduce the viscosity of the electrolytic solution. Can help.

  Such a fluorine-containing non-aqueous solvent is 1% by mass or more (typically 5% by mass to 100% by mass, for example, 30% by mass) of all components (components other than the supporting salt) excluding the supporting salt from the electrolytic solution. ˜100% by mass, preferably 50% by mass to 100% by mass). Substantially 100% by mass (typically 99% by mass or more) of the components other than the supporting salt may be a fluorine-containing non-aqueous solvent. Or the electrolyte solution of the composition containing a fluorine-containing nonaqueous solvent and the nonaqueous solvent which does not contain a fluorine as a structural element may be sufficient. In this case, the proportion of the non-aqueous solvent containing no fluorine atom is preferably, for example, a proportion of 70% by mass or less of components other than the supporting salt contained in the electrolytic solution, and more preferably 60% by mass (for example, 50%). Mass%) or less.

  The electrolytic solution used in the technology disclosed herein can also appropriately contain components other than the nonaqueous solvent and the supporting electrolyte as long as the effects of the present invention are not significantly impaired. Examples of such optional components include film forming agents such as lithium bis (oxalato) borate (LiBOB), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC); biphenyl (BP), cyclohexyl Various additives such as a compound capable of generating a gas upon overcharge, such as benzene (CHB); a dispersant such as carboxymethylcellulose (CMC); a thickener;

In another preferred embodiment, the reduction potential (vs. Li ^/ Li ⁺ ) of the electrolytic solution is desirably equal to or lower than the lower limit operating potential (vs. Li ^/ Li ⁺ ) of the negative electrode active material. For example, the difference from the operating potential (vs. Li ^/ Li ⁺ ) of the negative electrode active material is greater than 0 V (typically about 0.1 V to 2.0 V, preferably about 0.2 V to 1.0 V). An electrolytic solution can be preferably employed.
The reduction potential (vs. Li ^/ Li ⁺ ) of the electrolytic solution can be measured by the following method. A tripolar cell was created using glassy carbon as the working electrode (WE), metallic lithium as the counter electrode (CE), metallic lithium as the reference electrode (RE), and the electrolyte to be measured. Measure linear sweep voltammetry. Specifically, at a temperature of 20 ° C., the potential of the working electrode is swept from the open circuit voltage (OCV) after cell formation to 0.05V. The sweep speed is 1 mV / sec. The differential value dI / dV is calculated from the current I and the potential V of the measurement result. A graph is created with dI / dV as the vertical axis and the potential V as the horizontal axis. In this graph, the potential V corresponding to the peak of dI / dV that first appears from the start of measurement is taken as the reduction potential (reduction decomposition potential). For example, the reduction potential of the electrolytic solution (nonaqueous electrolyte containing LiPF ₆ at a concentration of 1 mol / L in a mixed solvent with a 1: 1 volume ratio of MFEC: TFDMC) used in Examples described later is approximately 1.9 V ( vs. Li ^/ Li ⁺ ).

<Battery case>
As a battery case, the material and shape conventionally used for a nonaqueous electrolyte secondary battery can be used. Examples of the material of the case include metal materials such as aluminum and steel; resin materials such as polyphenylene sulfide resin and polyimide resin. Among them, a relatively light metal (for example, aluminum or aluminum alloy) can be preferably employed for the purpose of improving heat dissipation and increasing energy density. The shape of the case (outer shape of the container) is, for example, circular (cylindrical shape, coin shape, button shape), hexahedron shape (rectangular shape, cubic shape), bag shape, and a shape obtained by processing and deforming them. It can be.

  Although not intended to be particularly limited, as a nonaqueous electrolyte secondary battery according to an embodiment of the present invention, an electrode body (winding electrode body) wound flatly, and a nonaqueous electrolyte, A non-aqueous electrolyte secondary battery (unit cell) in a form accommodated in a flat rectangular parallelepiped (rectangular) container is taken as an example, and FIGS. In the following drawings, members / parts having the same action are denoted by the same reference numerals, and redundant description may be omitted or simplified. The dimensional relationship (length, width, thickness, etc.) in each figure does not reflect the actual dimensional relationship.

  In the nonaqueous electrolyte secondary battery according to an embodiment of the technology disclosed herein, for example, as shown in FIGS. 1 and 2, the wound electrode body 80 and the nonaqueous electrolyte 90 have a shape of the electrode body 80. In a battery case 50 having a flat rectangular parallelepiped shape (rectangular shape). The battery case 50 includes a flat rectangular parallelepiped (square) battery case main body 52 having an open upper end, and a lid 54 that closes the opening. A positive electrode terminal 70 and a negative electrode terminal 72 for external connection are provided on the upper surface (that is, the lid body 54) of the battery case 50 so that some of the terminals protrude from the lid body 54 to the outside of the battery. . The lid 54 is provided with a safety valve 55 for discharging gas that can be generated inside the battery case to the outside.

As shown in FIGS. 2 and 3, the wound electrode body 80 includes a positive electrode sheet 10 in which a positive electrode active material layer 14 containing a positive electrode active material is held on both surfaces of a long sheet-like positive electrode current collector 12, and a negative electrode A negative electrode sheet 20 in which a negative electrode active material layer 24 containing an active material is held on both surfaces of a long sheet-like negative electrode current collector 22 and two long sheet-like separators 40 are overlapped and wound to obtain The wound body is formed into a flat shape by pressing and curling it from the side. In the example illustrated in FIG. 3, when the wound electrode body 80 is manufactured, the four sheets are stacked in the order of the separator sheet 40, the negative electrode sheet 20, the separator sheet 40, and the positive electrode sheet 10 from the bottom. Further, the positive electrode sheet 10 and the positive electrode sheet 10 so that the uncoated portion of the positive electrode active material layer 14 of the positive electrode sheet 10 and the uncoated portion of the negative electrode active material layer 24 of the negative electrode sheet 20 protrude from both sides in the width direction of the separator 40, respectively. The negative electrode sheet 20 is overlaid with a slight shift in the width direction. A flat wound electrode body 80 can be produced by winding the electrode bodies stacked in this way and pressing them from a direction perpendicular to the winding axis WL. A positive electrode terminal 70 is joined to the uncoated part of the positive electrode current collector 12, and a negative electrode terminal 72 is joined to the uncoated part of the negative electrode current collector 22.
For example, the non-aqueous electrolyte secondary battery 100 having such a configuration is provided in the lid body 54 after the electrode body 80 is accommodated inside the opening portion of the case 50 and the lid body 54 is attached to the opening portion of the case 50. It can be constructed by injecting an electrolytic solution 90 from an electrolytic solution injection hole (not shown) and then closing the injection hole.

  The non-aqueous electrolyte secondary battery (typically a lithium ion secondary battery) disclosed here can be used for various applications. Since the elution of the metal element from the positive electrode active material is suitably suppressed and the battery performance (for example, energy density and durability) is excellent, this feature is utilized, for example, as shown in FIG. It can be suitably used as a driving power source. The vehicle 1 is typically an automobile, and may be, for example, a hybrid automobile (HV), a plug-in hybrid automobile (PHV), an electric automobile (EV), a fuel cell automobile, an electric wheelchair, or an electric assist bicycle. Therefore, as another aspect of the present invention, there is provided a vehicle 1 provided with any of the nonaqueous electrolyte secondary batteries 100 disclosed herein, preferably as a power source. The vehicle 1 may be provided with a plurality of nonaqueous electrolyte secondary batteries 100, typically in the form of an assembled battery to which they are connected.

  Hereinafter, some examples relating to the present invention will be described, but the present invention is not intended to be limited to such examples. In the following description, “parts” and “%” are based on mass unless otherwise specified.

<Preparation of positive electrode active material particles (surface-coated FT-LNM particles)>
As raw material particles, LiNi _0.45 Fe _0.05 Mn _1.45 Ti _0.05 O ₄ particles (FT-LNM spinel particles) having an average particle diameter of 6 μm and a BET specific surface area of 0.7 m ² / g were prepared. Hereinafter, the FT-LNM spinel particles are also referred to as “FT-LNM raw material particles”.
LiNO ₃ and (NH ₄ ) ₂ HPO ₄ were mixed and dissolved in deionized water. This solution was dried to prepare a powder (precursor powder) serving as a precursor of the outer region (low Mn region).
This precursor powder and the above-mentioned FT-LNM raw material particles were put into a coating apparatus for coating with collision energy between particles utilizing centrifugal force, and a coating treatment was performed for 30 minutes at a rotational speed of 5000 rpm. As the coating apparatus, model “Nobilta NOB-MINI” manufactured by Hosokawa Micron Corporation was used. The obtained precursor with FT-LNM material particles and baked for 4 hours at 400 ° C. in air, to produce a _Li 3 PO ₄ from the precursor powder. In this way, positive electrode active material particles (surface-coated FT-LNM particles) in which the surface of the FT-LNM raw material particles was coated with the Li ₃ PO ₄ layer as the outer region were obtained. The average particle size of the surface-coated FT-LNM particles was 6 μm, and the BET specific surface area was 0.7 m ² / g.

<Preparation of nonaqueous electrolyte secondary battery>
(Battery A0)
The surface-coated FT-LNM particles produced above, acetylene black (conductive material), and PVdF (binder) were dispersed in NMP so that the mass ratio thereof was 89: 8: 3, A composition was prepared. This composition was applied to one side of a 15 μm thick long aluminum foil (positive electrode current collector) and dried to form a positive electrode active material layer. The current collector with the positive electrode active material layer was roll-pressed to adjust the density of the positive electrode active material layer to 2.3 g / cm ³ and cut into a predetermined rectangular shape. In this way, a positive electrode sheet having a theoretical capacity (design capacity) _CC of 60 mAh was obtained.
A natural graphite material having an average particle diameter of 20 μm and a BET specific surface area of 2.5 m ² / g was prepared as a negative electrode active material. This negative electrode active material, CMC, and SBR were mixed with ion-exchanged water so that the mass ratio thereof was 98: 1: 1 to prepare a slurry composition. This composition was applied to one side of a 10 μm thick copper foil (negative electrode current collector) and dried to form a negative electrode active material layer. The current collector with the negative electrode active material layer was roll-pressed to adjust the density of the negative electrode active material layer to 1.4 g / cm ³ and cut into a rectangular shape having the same size as the positive electrode sheet to obtain a negative electrode sheet. The coating amount of the composition was adjusted so that the theoretical capacity ratio (C _c / C _a ) between the positive electrode and the negative electrode was 1.5.
The positive electrode sheet and the negative electrode sheet prepared above were opposed to each other through a separator sheet (a porous sheet having a PP / PE / PP three-layer structure), and wound to prepare a wound electrode body.

Mixed solvent containing MFEC as cyclic carbonate and TFDMC as chain carbonate (that is, fluoromethyldifluoromethyl carbonate represented by FH ₂ CO (C═O) OCHF ₂ ) in a volume ratio of 1: 1. LiPF ₆ was dissolved to a concentration of 1 mol / L to prepare a non-aqueous electrolyte S0. The oxidation potential and reduction potential of this non-aqueous electrolyte were measured according to the method described above. The oxidation potential was 4.9 to 5.1 V (vs. Li / Li ⁺ ), and the reduction potential was 1.9 V (vs. Li / Li ⁺ ).
The electrode body and the non-aqueous electrolyte were accommodated in a battery case made of a laminate film of an appropriate size and sealed to construct a lithium ion secondary battery A0. The positive electrode sheet and the negative electrode sheet are provided with a positive electrode terminal and a negative electrode terminal, respectively, drawn to the outside of the battery case.

(Battery A1)
A non-aqueous electrolyte S1 having an acetylacetone concentration of 1.6% by mass (about 0.16 mol / L) is obtained by further dissolving acetylacetone as a transition metal ion scavenger in the non-aqueous electrolyte S0 used for producing the battery A0. Was prepared. A lithium ion secondary battery A1 was produced in the same manner as in the production of the battery A0 except that this nonaqueous electrolytic solution S1 was used.

(Battery B0)
In the production of the battery A0, instead of the surface-coated FT-LNM particles, LiNi _0.45 Fe _0.05 Mn _1.45 Ti _0.05 O ₄ particles having an average particle diameter of 6 μm and a BET specific surface area of 0.7 m ² / g (FT-LNM spinel particles) was used. Otherwise, the lithium ion secondary battery B0 was produced in the same manner as the battery A0.
(Battery B1)
A lithium ion secondary battery B1 was produced in the same manner as the battery B0 except that the nonaqueous electrolyte S1 containing acetylacetone was used.

(Battery C0)
In the production of the battery A0, instead of the surface-coated FT-LNM particles, LiNi _0.5 Mn _1.5 O ₄ particles having an average particle diameter of 6 μm and a BET specific surface area of 0.7 m ² / g (ie, substantially as a metal element) Lithium-nickel-manganese spinel particles containing only Li, Ni, and Mn, hereinafter also referred to as “LNM spinel particles”). Otherwise, the lithium ion secondary battery C0 was produced in the same manner as the battery A0.
(Battery C1)
A lithium ion secondary battery C1 was produced in the same manner as the production of the battery C0 except that the nonaqueous electrolytic solution S1 containing acetylacetone was used.

<Conditioning>

<Performance evaluation>
(Initial capacity)
Each battery was conditioned at a temperature of 25 ° C. with the following charge / discharge pattern.
(1) After a constant current (CC) charge to 4.9 V at a rate of 1/3 C, pause for 10 minutes.
(2) After discharging CC to 3.5 V at a rate of 1/3 C, pause for 10 minutes.
The above operations (1) and (2) were repeated three cycles, and the discharge capacity at the third cycle was defined as the initial capacity (initial discharge capacity).

(Cycle characteristic test)
Each battery after the conditioning was allowed to stand in a thermostat set at a temperature of 60 ° C. for 2 hours or longer, and the following charge / discharge operations (1) to (4) were repeated 200 cycles.
(1) CC charge to 4.9V at 2C rate.
(2) Pause for 10 minutes.
(3) CC discharge to 3.5V at a rate of 2C.
(4) Pause for 10 minutes.
Thereafter, the discharge capacity (capacity after 200 cycles) was measured at a temperature of 25 ° C. in the same manner as the initial capacity. The capacity retention rate (%) by this cycle characteristic test was calculated as the ratio of the capacity after 200 cycles to the initial capacity ((capacity after 200 cycles / initial capacity) × 100 (%)).

  In order to evaluate the effect of the transition metal ion scavenger (here, acetylacetone) contained in the nonaqueous electrolyte on the durability of the battery, the nonaqueous electrolyte S0 containing no transition metal ion scavenger was used. The capacity maintenance rates of the batteries A0, B0, C0 are 100 (standard), respectively, and the capacity maintenance rates of the corresponding batteries A1, B1, C1 using the non-aqueous electrolyte S1 containing the transition metal ion scavenger are designated as the battery A0, It was calculated as a relative value with respect to B0 and C0. The results are shown in Table 1 for batteries A0 and A1 using surface-coated FT-LNM particles, in Table 2 for batteries B0 and B1 using FT-LNM spinel particles, and battery C0 using LNM spinel particles. And C1 are shown in Table 3.

  As is clear from these tables, in the battery using the FT-LNM spinel particles or the LNM spinel particles, which are the positive electrode active material particles having no outer region, by adding a transition metal ion scavenger to the nonaqueous electrolyte, The capacity retention rate was significantly reduced to 1/20 or less of the standard value (Tables 2 and 3).

  On the other hand, in a battery using positive electrode active material particles (surface-coated FT-LNM particles) formed by forming an outer region on FT-LNM spinel particles, the capacity retention rate is standard due to the use of a transition metal ion scavenger. It improved about 5% from the value (Table 1). That is, the function of the transition metal ion scavenger was appropriately exhibited, and the effect of improving the durability of the battery was obtained.

As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here.
For example, as a method for obtaining the positive electrode active material particles, in addition to the surface coating method described above, a method including modifying at least a part of the surface region of the raw material particles into an outer region (surface modification method) is exemplified. can do. A combination of the surface modification method and the surface coating method may be applied.
In the surface modification method, for example, the above-described FT-LNM raw material particles are used, and the Mn concentration in the surface region of the FT-LNM raw material particles is made lower than the basic composition (that is, the composition of the central region). The positive electrode active material particles in which the surface region is modified to the outer region (low Mn region) can be obtained. As a method for reducing the Mn concentration in the surface region, for example, the modification treatment liquid containing the transition metal ion scavenger as described above is brought into contact with the raw material particles, and at least a part of Mn contained in the surface region is brought into contact. The removal method can be preferably employed. The time (treatment time) for bringing the modification treatment liquid into contact with the raw material particles is, for example, 10 minutes or more (typically 10 minutes to 6 hours, preferably 15 minutes to 3) in view of the balance between the treatment efficiency and the modification effect. Time). Thereafter, the resulting product (that is, processed raw material particles) is separated from the processing liquid. If necessary, the resulting product may be subjected to post-treatment such as washing, drying and heating. The heat treatment may be, for example, a treatment for holding the resultant product at a temperature of 150 ° C. or higher (typically 200 ° C. or higher, preferably 250 ° C. or higher, more preferably 300 ° C. or higher, eg 350 ° C. or higher). . Such heat treatment can be useful for alleviating strain and crystallinity degradation that may be caused by modifying the surface region. Thereby, positive electrode active material particles with better durability can be realized. The heat treatment can also serve to decompose or volatilize organic matter that may be included in the result. The upper limit of the heat treatment temperature is usually suitably 500 ° C. or less, preferably 450 ° C. or less (eg, about 400 ° C.). The heat treatment time can be usually about 30 minutes to 48 hours (typically 1 hour to 24 hours, for example, 2 hours to 12 hours). The heat treatment is usually preferably performed in an oxidizing atmosphere (for example, an air atmosphere).

1 Automobile (vehicle)
10 Positive electrode sheet (positive electrode)
12 Positive electrode current collector 14 Positive electrode active material layer 20 Negative electrode sheet (negative electrode)
22 Negative electrode current collector 24 Negative electrode active material layer 40 Separator sheet (separator)
DESCRIPTION OF SYMBOLS 50 Battery case 52 Battery case main body 54 Cover body 55 Safety valve 70 Positive electrode terminal 72 Negative electrode terminal 80 Winding electrode body 90 Electrolyte (nonaqueous electrolyte)
100 Non-aqueous electrolyte secondary battery

Claims (6)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The positive electrode is
Comprising positive electrode active material particles having a lithium transition metal compound as a basic composition, and an operating upper limit potential of 4.5 V or more based on metallic lithium;
The positive electrode active material particles are:
A central region having the basic composition;
An outer region that covers the outside of the central region and does not contain at least one transition metal contained in the basic composition or has a lower concentration of the transition metal than the basic composition;
The nonaqueous electrolyte is a nonaqueous electrolyte secondary battery containing a transition metal ion scavenger.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the outer region is a coating layer having lithium ion conductivity.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the basic composition is a lithium nickel manganese oxide having a spinel structure. The basic composition has the following general formula (1):
_{Li x (Ni 0.5-a Fe} P Mn 1.5-b Ti Q M 0 R) O 4 + d (1)
(Here, M ⁰ is an element other than Ni, Mn, Fe, Ti, 0.9 ≦ x ≦ 1.2, 0 ≦ a, −0.1 ≦ b, 0 < P ≦ 0.1, 0 <Q ≦ 0.1, 0 ≦ R, a + b = P + Q + R, d is −0.2 ≦ d ≦ 0.2, and charge neutrality condition It is a value that is determined to satisfy.);
The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, which has a composition represented by: A method for producing a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the operating upper limit potential of the positive electrode is 4.5 V or more based on metallic lithium:
Providing a positive electrode comprising positive electrode active material particles having a lithium transition metal compound as a basic composition;
Providing a non-aqueous electrolyte comprising a transition metal ion scavenger; and
Constructing a non-aqueous electrolyte secondary battery using the positive electrode and the non-aqueous electrolyte;
Including
Here, the positive electrode active material particles are:
A central region having the basic composition;
A method for producing a non-aqueous electrolyte secondary battery, comprising an outer region that covers the outside of the central region and does not contain a transition metal or has a lower transition metal concentration than the basic composition.   A vehicle comprising the nonaqueous electrolyte secondary battery according to any one of claims 1 to 4 or the nonaqueous electrolyte secondary battery produced by the method according to claim 5.

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