KR20160056319A - Positive active material for sodium rechargeable batteries and method of manufacturing the same - Google Patents

Abstract

The present invention relates to a positive electrode active material for a sodium secondary battery, and a producing method thereof and, more specifically, to a positive electrode active material for a sodium secondary battery, having a novel O_3 structure, and a producing method thereof. The positive electrode active material for a sodium secondary battery according to the present invention has an O_3 structure and thus is structurally stable, unlike a conventional positive electrode active material, so a sodium battery comprising the positive electrode active material for a sodium secondary battery according to the present invention exhibits excellent lifespan characteristics.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode active material for a sodium secondary battery and a cathode active material for a sodium secondary battery,

The present invention relates to a cathode active material for a sodium secondary battery and a method of manufacturing the same, and more particularly, to a cathode active material for a sodium secondary battery having a novel O ₃ structure and a method for manufacturing the same.

Currently, a lithium ion secondary battery in which a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent is used as a secondary battery of high energy density, and charge / discharge is performed by moving lithium ions between an anode and a cathode is widely used. As a cathode material, a lithium ion battery using an intermediate insertion reaction of lithium ions using a lithium transition metal oxide has been commercialized. However, since lithium contained in a lithium ion battery is expensive, a battery having a lower cost and a higher capacity is required.

Recently, research on a sodium ion secondary battery using sodium ion instead of lithium ion has been started. Since sodium is abundant in resource reserves, it is possible to manufacture a secondary battery at low cost if a secondary battery using sodium ion can be manufactured instead of lithium ion.

Japanese Patent Application Laid-Open No. 2007-287661 discloses a positive electrode using a composite metal oxide obtained by firing a raw material having a composition ratio of Na, Mn and Co (Na: Mn: Co) of 0.7: 0.5: 0.5 and a negative electrode made of a sodium metal A secondary battery is specifically described. Japanese Patent Application Laid-Open No. 2005-317511 discloses α-NaFeO ₂ having a hexagonal (layered salt salt) crystal structure as a metal oxide, and Na ₂ O ₂ and Fe ₃ O ₄ are mixed And then calcined in air at 600 to 700 ° C to obtain the composite metal oxide. However, the conventional sodium secondary battery can not be said to have a sufficient lifetime characteristic, that is, the discharge capacity retention rate when charging / discharging is repeated.

Japanese Patent Application Laid-Open No. 2007-287661 Japanese Patent Application Laid-Open No. 2005-317511

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a cathode active material for a sodium secondary battery having improved life characteristics and a method for manufacturing the same.

The invention Na _x [Ni _y Fe _1-yz Mn _z] O ₂ in order to solve the problems as described above (0? X? 1.2, 0.05? Y? 0.3, 0.05? Z? 0.9, and 0.05? 1-yz? 0.9) and having an O ₃ crystal structure.

The cathode active material for a sodium secondary battery according to the present invention is spherical particles having a particle size of 5 to 15 탆, and the particle size distribution is monodisperse.

The cathode active material for a sodium secondary battery according to the present invention is characterized in that XRD exhibits three peaks in 2 [theta] range from 30 [deg.] To 40 [deg.].

The positive electrode active material for a sodium secondary battery according to the present invention is characterized in that XRD shows a (104) peak having a main peak in the range of 2 [theta] of 40 [deg.] To 45 [deg.].

The cathode active material for a sodium secondary battery according to the present invention has a tap density of 1.0 to 2.4 g / cc.

The present invention also relates to

Mixing a sodium compound with a cathode active material precursor for a sodium secondary battery; And

The present invention also provides a method for producing a cathode active material for a sodium secondary battery, comprising the steps of:

In the method for producing a cathode active material for a sodium secondary battery according to the present invention, the cathode active material precursor for a sodium secondary battery is represented by any one of the following formulas (1) to (3).

???????? Ni _{x '} Fe _y' Mn _{1 -x'- y '} (OH) _{2 ,}

???????? Ni _{x '} Fe _y' Mn _{1 -x'- y '} C ₂ O _{4 ,}

[Formula 3] [Ni _{x '} Fe _y' Mn _{1 -x'-y '} ] ₃ O ₄

(In the above Chemical Formulas 1 to 3 0.05≤x'≤0.3, 0.1≤y'≤0.9, 0.05≤1-x' -y'≤0.9)

The positive electrode active material precursor for the sodium secondary battery is preferably prepared by coprecipitation, such as Applicants' number 10-2012-0130824, filed November 19,

That is, the cathode active material precursor for the sodium secondary battery comprises

(a) adding distilled water and a first pH adjusting agent to a coprecipitation reactor, supplying air or a nitrogen gas and maintaining the pH of the inside of the reactor at 6.5 to 7.5 while stirring;

(b) continuously introducing a second pH adjusting agent into the reactor and then mixing to adjust the pH in the reactor to 6.5 to 11; And

(c) an aqueous solution of a transition metal compound containing a nickel salt, an iron salt, and a manganese salt in an equivalent ratio, and a complexing agent to form precursor particles of a cathode active material for a sodium secondary battery.

In the method for preparing the positive electrode active material precursor for a sodium secondary battery, the second pH adjusting agent in step (b) is selected from the group consisting of ammonium oxalate, NaOH, and KOH.

In the method for preparing a cathode active material precursor according to the present invention, when KOH or NaOH is added as the second pH adjuster in the step (b), the pH in the reactor is adjusted to 9 to 11, and as the second pH adjuster, The pH in the reactor is adjusted to 6.5 to 11.

In the method for producing a precursor of a cathode active material for a sodium secondary battery according to the present invention, the nickel salt in the step (c) is selected from the group consisting of nickel sulfate, nickel nitrate, nickel chloride and nickel fluoride, Iron nitrate, iron chloride, iron fluoride, and the manganese salt is characterized by being selected from manganese sulfate, manganese nitrate, manganese chloride and manganese fluoride.

In a sodium secondary battery, the positive electrode active material precursor production process of the present invention, the (c) the complexing agent in step is an aqueous ammonia solution (NH ₄ OH), ammonium sulfate _{((NH 4) 2 SO 4} ), ammonium nitrate (NH ₄ NO ₃ ) and ammonium monophosphate ((NH ₄ ) ₂ HPO ₄ ).

In the method for producing a precursor of a cathode active material for a sodium secondary battery according to the present invention, the ratio of the concentration of the complexing agent to the concentration of the aqueous solution of the transition metal compound in the step (c) is 0.8 to 1.2.

In the method for producing a cathode active material for a sodium secondary battery according to the present invention, the sodium compound is one of sodium carbonate, sodium nitrate, sodium acetate, sodium hydroxide, sodium hydroxide hydrate, sodium oxide or a combination thereof.

In the method of preparing a cathode active material for a sodium secondary battery according to the present invention, in the step of mixing a sodium compound with a cathode active material precursor for a sodium secondary battery, the sodium compound is mixed at a ratio of 1.0 to 1.5 mol per 1 mole of the cathode active material precursor for the sodium secondary battery .

In the method of manufacturing a cathode active material for a sodium secondary battery according to the present invention, the heat treatment is performed at 800 ° C to 1000 ° C.

The sodium secondary battery cathode active material according to the present invention is structurally stable with an O ₃ structure unlike the prior art, and thus the sodium battery including the sodium secondary battery cathode active material according to the present invention exhibits excellent lifetime characteristics.

FIGS. 1 to 4 show SEM photographs of the precursors prepared in the examples of the present invention.
5 to 8 show the results of measuring the particle size distribution of the precursor produced in the examples of the present invention.
Figure 9 shows the results of XRD measurements of the precursors prepared in the examples of the present invention.
10 shows the results of measuring the particle size distribution of the precursor prepared in the examples of the present invention.
FIGS. 11 and 12 show SEM photographs of the precursors prepared in the examples of the present invention.
13 and 14 show the results of measuring the particle size distribution of the precursor produced in the examples of the present invention.
15 to 22 show the results of XRD measurements of the cathode active material prepared in the examples of the present invention.
FIGS. 23 to 33 show results of measurement of lifetime characteristics or charge / discharge characteristics of a sodium secondary battery including a cathode active material manufactured in an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

< Example  1 to 4>

The reactor was charged with 4 L of distilled water and stirred at 1000 rpm while adding ammonia to maintain the internal pH of the reactor at 7 and the internal temperature at 50 ° C. 4M NaOH solution was added as a second pH adjusting agent to adjust the internal pH of the reactor to 10.2 and maintained for 30 minutes.

NiSO ₄ .6H ₂ O, FeSO ₄ .7H ₂ O and MnSO ₄ .5H ₂ O were mixed in an equivalent ratio to an aqueous solution of a transition metal compound and introduced into the reactor together with NH ₄ OH as a complexing agent, Precursor.

As shown in the following Table 1, except that the mixing ratio of the aqueous solution of the transition metal compound in Example 1 was controlled, Ni _0.25 Fe _0.35 Mn _0.4 (OH) ₂ , Ni _{0 . 25} Fe _{0 . 5} Mn _{0 .25} (OH) ₂ and Ni _{0 . 15} Fe _{0 . 35} Mn _{0 . 5} (OH) _2. &Lt; / RTI &gt;

division Precursor composition Example 1 Ni _{0 . 25 Fe 0.25 Mn 0 .5 (OH} ) 2 Example 2 Ni _{0 . 25} Fe _{0 . 35 Mn 0 .4 (OH) 2} , Example 3 Ni _{0 . 25} Fe _{0 . 5} Mn _{0 .25} (OH) ₂ Example 4 Ni _0.15 Fe _0.35 Mn _0.5 (OH) ₂ Example 5 Ni _0.25 Fe _0.5 Mn _0.25 C ₂ O ₄ Example 6 Ni _{0 . 2} Fe _{0 . 6} Mn _{0 . 2} C ₂ O ₄ Example 7 Ni _0.17 Fe _0.66 Mn _0.17 C ₂ O ₄ Example 8 Ni _0.2 Fe _0.55 Mn _0.25 C ₂ O ₄ Example 9 Ni _0.3 Fe _0.45 Mn _0.25 C ₂ O ₄ Example 10 Ni _0.35 Fe _0.4 Mn _0.25 C ₂ O ₄ Example 11 (Ni _0.25 Fe _0.5 Mn _0.25 ) ₃ O ₄ Example 12 (Ni _0.25 Fe _0.25 Mn _0.5 ) ₃ O ₄

< Experimental Example  1> SEM  Photo measurement

SEM photographs of the precursors prepared in Examples 1 to 4 were measured and shown in Figs. 1 to 4. Fig.

< Experimental Example  2> Measurement of particle size distribution

The particle size distributions of the precursors prepared in Examples 1 to 4 were measured and shown in FIGS. 5 to 8. FIG. In FIGS. 5 to 8, it can be seen that the particle sizes of the precursor particles are monodisperse.

< Example  5 to 10> Ni _{x '} Fe _{y '} Mn _{One -x'- y '} C ₂ O ₄  Precursor manufacture

The same procedure as in Example 1 was carried out except that ammonia was used as the first pH adjusting agent and the internal pH of the reactor was adjusted to 7 and the internal pH of the reactor was adjusted to 7 using 0.5 M ammonium oxalate aqueous solution as the second pH adjusting agent The precursors of Examples 5 to 10 having compositions as shown in Table 1 were prepared.

< Experimental Example  3> XRD  Measure

The XRD of the precursors prepared in Examples 5 to 7 was measured and shown in FIG.

< Experimental Example  4> Measurement of particle size distribution

The particle size distributions of the precursors prepared in Examples 5 to 7 were measured and shown in FIG.

< Example  11, 12>

The procedure of Example 1 was repeated except that ammonia was used as the first pH adjusting agent and the internal pH of the reactor was adjusted to 7 and 4 M NaOH was added as the second pH adjusting agent to adjust the internal pH of the reactor to 9.2 _{0. 25 Fe 0. 5 Mn} 0. 25) 3 O 4, (Ni 0.25 Fe 0.25 Mn 0.5) was prepared in a precursor of the example 11, example 12 represented by the ₃ O _4.

< Experimental Example  5> SEM  Photo measurement

SEM photographs of the precursors prepared in Examples 11 and 12 were measured and shown in FIGS. 11 and 12. FIG.

< Experimental Example  6> Measurement of particle size distribution

The particle size distributions of the precursors prepared in Examples 11 and 12 were measured and shown in Figs. 13 and 14. Fig. 13 and 14, it can be seen that the particle size distribution is monodispersed.

< Example  13 to 24> Cathode active material  Produce

In Table 1, the precursor prepared in Examples 1 to 12 and sodium carbonate as sodium compounds were mixed and stirred and then heat-treated to prepare cathode active materials of Examples 13 to 24.

< Experimental Example > XRD  Measure

The results of XRD measurements of the cathode active materials of Examples 13 to 16 are shown in FIGS. 15 to 18, and the results of XRD measurements of the cathode active materials of Examples 17 to 19 are shown in FIG. 19, FIG. 20 shows the results of XRD measurements of the cathode active materials 20 to 22, and FIG. 21 and FIG. 22 show the results of XRD measurements of the cathode active materials of Examples 23 and 24.

15 to conduct a sodium secondary battery, the positive electrode active material produced in Example of the present invention in FIG. 22 is a 2θ in XRD shows the three peaks in the range of 30 ° to 40 °, 2θ is O ₃ in the range of 40 ° to 45 ° (104) main peak characteristic of the crystal structure appears.

< Manufacturing example > Manufacture of batteries

(Polyvinylidene difluoride polyfluoron) manufactured by Kureha Kabushiki Kaisha) as a binder were mixed with a mixed metal oxide E1, a mixed metal oxide E1, an acetylene black as a conductive material (manufactured by Denki Kagaku Kagaku Co., Ltd.) : Conductive material: binder = 85: 10: 5 (weight ratio).

Thereafter, the composite metal oxide and the acetylene black were thoroughly mixed with an agate mortar, and a proper amount of N-methyl-2-pyrrolidone (NMP: manufactured by Tokyo Kasei Kogyo K.K.) was added to the mixture, PVDF was added thereto, followed by mixing so as to be homogeneous and slurried. The slurry thus obtained was applied on an aluminum foil having a thickness of 40 mu m as a current collector to a thickness of 100 mu m using an applicator, and this was placed in a drier and sufficiently dried while removing NMP to obtain a positive electrode sheet. The positive electrode sheet was punched with a diameter of 1.5 cm by an electrode punching machine, and sufficiently pressed with a hand press to produce a positive electrode.

A positive electrode prepared with an aluminum foil downward was placed in a concave portion of a lower part of a coin cell (manufactured by Hosenkobe Chemical Co., Ltd.), and then 1 M of NaClO ₄ / propylene carbonate + 2 vol% fluoroethylene carbonate (FEC, Fluoro Ethylene Carbonate), a polypropylene porous film (thickness: 20 占 퐉) as a separator, and sodium metal as a cathode were combined to prepare a sodium secondary battery.

< Experimental Example > Charging and discharging  Characterization

The charge and discharge characteristics of the sodium secondary battery including the active materials of Examples 13 to 19 and 23 made of the precursors of Examples 1 to 7 and 11 were measured and the results are shown in Table 2 below.

division Sintering condition and charge / discharge condition 0.2C  One ^st One ^st Efficiency Example 1
Example 13 Ni _{0 . 25} Fe _{0 . 25} Mn _{0 . 5} (OH) ₂ precursor
Na 95%, 970 ° C / 24h sintering, 4.3V 155.5 mAh / g 94.1% Example 2
Example 14 Ni _{0 . 25} Fe _{0 . 35} Mn _{0 . 4} (OH) ₂ precursor
, Na 98%, 900 DEG C / 24h sintering, 4.3V 180.1 mAh / g 101.2% Ni _{0 . 25} Fe _{0 . 35} Mn _{0 . 4} (OH) ₂ precursor
Na 98%, 930 ° C / 24h sintering, 4.3V 176.3 mAh / g  100.9% Ni _{0 . 25} Fe _{0 . 35} Mn _{0 . 4} (OH) ₂ precursor
Na 98%, 970 ° C / 24h sintering, 4.3V 166.2 mAh / g 95.4% Example 3
Example 15 Ni _{0 . 25} Fe _{0 . 5} Mn _{0 . 25} (OH) ₂ precursor
Na 98%, 970 ° C / 24h sintering, 3.9V 130.7 mAh / g 91.6% Example 4
Example 16 Ni _{0 . 15} Fe _{0 . 35} Mn _{0 .5} (OH) ₂ precursor
Na 98%, 970 ° C / 24h sintering, 4.3V 141.3 mAh / g 104% Example 5
Example 17 Ni _{0 . 25} Fe _{0 . 5} Mn _{0 . 25} C ₂ O ₄ Precursor
Na 98%, 950 ° C / 24h sintering, 3.9V 135.7 mAh / g 93.4% Example 6
Example 18 Ni _{0 . 2} Fe _{0 . 6} Mn _{0 . 2} C ₂ O ₄ precursor
Na 98%, 950 ° C / 24h sintering, 3.8V 123.0 mAh / g 93.6% Example 7
Example 19 Ni _{0 . 17} Fe _{0 . 66} Mn _{0 . 17} C ₂ O ₄ , precursor
Na 98%, 950 ° C / 24h sintering, 3.7V 116.8 mAh / g 91.8% Example 11
Example 23 _{(Ni 0. 25 Fe 0.} 5 Mn 0. 25) 3 O 4 precursor
Na 98%, 970 ° C / 24h sintering, 3.9V 124.3 mAh / g 92.1%

In Table 2, it can be seen that the initial charge-discharge efficiency of the battery including the cathode active material of the O ₃ crystal structure manufactured by the present invention is more than 90%.

< Experimental Example > Life characteristics measurement

The charge / discharge characteristics of the sodium secondary battery including the active material of the O ₃ crystal structure of Examples 13 to 16 and Example 23 made of the precursors of Examples 1 to 4 and Example 11 were measured and the results are shown in Table 3 below And the charge / discharge characteristics of the sodium secondary battery including the active material of the O ₃ crystal structure of Examples 17 to 19 made of the precursors of Examples 5 to 7 were measured, and the results are shown in FIG.

division 0.2C  One ^st 0.2C  20 ^th 0.2C retention 0.5 C  One ^st 0.5 C  20 ^th 0.5 C
retention Example 1
Example 13 155.5 mAh / g 130.2 mAh / g 83.7% 106.9 mAh / g 96.0 mAh / g 89.8% Example 2
Example 14 180.1 mAh / g 141.3 mAh / g 78.5% 125.6 mAh / g 117.5 mAh / g 93.6% 176.3 mAh / g 140.5 mAh / g 76.7% 125.9 mAh / g 117.8 mAh / g 93.6% 166.2 mAh / g 124.6 mAh / g 75.0% 107.7 mAh / g 95.1 mAh / g 88.3% Example 3
Example 15 130.7 mAh / g 122.0 mAh / g 93.3% 114.3 mAh / g 105.4 mAh / g 92.2% Example 4
Example 16 141.3 mAh / g 119.9 mAh / g 84.9% 90.7 mAh / g 81.7 mAh / g 90.1% Example 11
Example 23 124.3 mAh / g 114.7 mAh / g 92.3% 106.5 mAh / g 100.7 mAh / g 94.6%

In Table 2 and FIG. 27, it can be seen that the sodium secondary battery including the active material having the O ₃ crystal structure according to the present invention exhibits a very high lifespan characteristic of about 90% up to 20 cycles.

< Experimental Example > Charging and discharging  Measurement of characteristics and life characteristics

The results of measuring the charge / discharge characteristics of the sodium secondary battery including the active material of Examples 13 to 16 are shown in FIGS. 23 to 26, and the charge / discharge characteristics and life characteristics of the sodium secondary batteries of Examples 17 to 19 were measured The results are shown in FIG. 27 and FIG. 28, and the results of measurement of charge / discharge characteristics and lifetime characteristics of a sodium secondary battery including the active material prepared in Examples 17 and 20 to 22 are shown in FIGS. 29 to 31, 23, and 24, the results of measurement of charge / discharge characteristics and lifetime characteristics of a sodium secondary battery including an active material of an O ₃ crystal structure are shown in FIGS. 32 and 33.

Claims (6)

Na _x [Ni _y Fe _z Mn _{1- y z} ] O ₂ (0? X? 1.2, 0.05? Y? 0.3, 0.05? Z? 0.9 and 0.05? 1-yz? 0.9) and is an O ₃ crystal structure and a spherical particle having a particle size of 5 to 15 μm, And a tap density of 1.0 to 2.4 g / cc in which the size distribution is a monodisperse type. The method according to claim 1,
Wherein the positive electrode active material for a sodium secondary battery exhibits three peaks in 2 [theta] range from 30 [deg.] To 40 [deg.] In XRD. 3. The method of claim 2,
Wherein the cathode active material for a sodium secondary battery exhibits a (104) peak in XRD with a main peak in the range of 2 [theta] of 40 [deg.] To 45 [deg.]. Mixing a precursor of a cathode active material for a sodium secondary battery represented by any one of Chemical Formulas 1 to 3 and a sodium compound in a ratio of 1.0 to 1.5 moles of the sodium compound per 1 mole of the precursor of the cathode active material for the sodium secondary battery; And
???????? Ni _{x '} Fe _y' Mn _{1 -x'- y '} (OH) _{2 ,}
???????? Ni _{x '} Fe _y' Mn _{1 -x'- y '} C ₂ O _{4 ,}
[Formula 3] [Ni _{x '} Fe _y' Mn _{1 -x'-y '} ] ₃ O ₄
(In the above Chemical Formulas 1 to 3 0.05≤x'≤0.3, 0.1≤y'≤0.9, 0.05≤1-x' -y'≤0.9)
A heat treatment step
A method for producing a cathode active material for a sodium secondary battery according to claim 1. 5. The method of claim 4,
Wherein the sodium compound is one of sodium carbonate, sodium nitrate, sodium acetate, sodium hydroxide, sodium hydroxide hydrate, sodium oxide or a combination thereof. 5. The method of claim 4,
Wherein the heat treatment is performed at a temperature of 800 ° C to 1000 ° C in the step of heat-treating the positive electrode active material for a sodium secondary battery.

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