Titanium phosphate sodium negative material and preparation method thereof and sodium ion battery

Abstract

The application relates to the technical field of batteries, in particular to a sodium titanophosphate negative material, a preparation method thereof and a sodium ion battery. The preparation method of the sodium titanophosphate negative material comprises the following steps: mixing a phosphorus source, a sodium source, a titanium source, a mixed carbon source and a boron source, and then sintering in an inert atmosphere to obtain the sodium titanophosphate negative material; wherein the mixed carbon source comprises at least two different carbon sources. The mixed carbon source composed of at least two different carbon sources is adopted for coating to improve the electronic conductivity of the sodium titanophosphate, so that the coulomb efficiency and the rate performance are improved; the addition of the boron source can improve the stability of the material itself, reduce the occurrence of side reactions, also can serve as a fluxing agent, improve the poor solid-phase crystallinity and the long preparation time, and improve the electrochemical performance of the sodium titanophosphate negative material. The method is simple in operation, low in cost and friendly to the environment.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a sodium titanium phosphate anode material, its preparation method, and a sodium-ion battery. Background Technology

[0002] Aqueous sodium-ion batteries are a novel battery technology with advantages such as high energy density, high safety, and environmental friendliness. Sodium titanium phosphate (STP) is a key material in aqueous sodium-ion batteries. Its relatively simple preparation and low cost give aqueous sodium-ion batteries greater commercial application potential. However, this material also has some drawbacks that require further improvement. First, STP has low electrochemical activity, resulting in low specific capacity and conductivity, limiting the battery's capacity and charge / discharge rate. Furthermore, STP is prone to structural damage and capacity decay during long-term cycling. The preparation method of STP directly affects the material's structure and performance. By optimizing the preparation method, STP materials with good electrochemical performance and chemical stability can be obtained, thereby improving the performance of aqueous sodium-ion batteries and promoting their application in the energy field. Therefore, research on its preparation method is of great significance.

[0003] To improve the electrochemical performance of sodium titanium phosphate, researchers have proposed several directions for improvement in material preparation. First, its electrochemical activity can be enhanced by altering its structure and composition. For example, introducing heteroatoms, doping, and surface modification can increase the number of active sites and improve its energy storage performance. Second, its conductivity can be improved by modifying the microstructure of sodium titanium phosphate and by carbon coating. However, traditional modification methods suffer from high cost and poor effectiveness of atomic doping, cumbersome preparation processes, and poor crystallinity in solid-state preparations. Therefore, researching a simple, low-cost, and effective modification method is of great significance for the practical application of aqueous sodium-ion batteries.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a method for preparing sodium titanium phosphate anode material. This method is simple to operate, low in cost, and environmentally friendly. It can improve the electrochemical activity of sodium titanium phosphate anode material and enhance the specific capacity, conductivity, rate performance, and cycle stability of the battery.

[0006] The second objective of this invention is to provide a sodium titanium phosphate anode material, which is prepared by the method described above.

[0007] A third objective of the present invention is to provide a sodium-ion battery comprising the sodium titanium phosphate anode material as described above.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] A method for preparing sodium titanium phosphate anode material includes the following steps:

[0010] The sodium titanium phosphate anode material is obtained by mixing phosphorus source, sodium source, titanium source, mixed carbon source and boron source and sintering in an inert atmosphere; wherein the mixed carbon source includes at least two different carbon sources.

[0011] Preferably, the phosphorus source, the sodium source, and the titanium source are measured in a P:Na:Ti molar ratio of 2.5-3.5:1:1.5-2.5.

[0012] Preferably, the amount of boron source added accounts for 1wt%-10wt% of the total mass of all raw materials.

[0013] Preferably, the amount of the mixed carbon source added is measured as 1wt%-10wt% of the theoretical carbon content of all raw materials.

[0014] Preferably, the boron source includes boric acid and / or boron oxide.

[0015] Preferably, the mixed carbon source includes at least two of graphite, glucose, sucrose, citric acid, starch, graphene, and carbon nanofibers.

[0016] More preferably, the mixed carbon source includes graphite and glucose.

[0017] More preferably, the mass ratio of the theoretical carbon content of the graphite and the glucose is 6:1 to 1:2.

[0018] Preferably, the phosphorus source includes at least one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, ammonium phosphate, and diammonium hydrogen phosphate.

[0019] Preferably, the sodium source includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, sodium carbonate, sodium bicarbonate, and sodium acetate.

[0020] Preferably, the titanium source includes at least one of titanium dioxide, metatitanic acid, and titanium trioxide.

[0021] Preferably, the mixing is ball milling.

[0022] Preferably, the sintering temperature is 500-1000℃ and the sintering time is 1-6h.

[0023] Preferably, the sintering heating rate is 1-10℃ / min.

[0024] A sodium titanium phosphate anode material is prepared by the method described above.

[0025] A sodium-ion battery comprising the negative electrode material as described above.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) The method of the present invention utilizes the different conductivity of different carbon sources and uses a mixed carbon source composed of at least two different carbon sources for coating to improve the electronic conductivity of sodium titanium phosphate, thereby improving the coulombic efficiency and rate performance; the addition of boron source can improve the stability of the material itself, making it less prone to side reactions, thereby improving its electrochemical performance. Boron source can also act as a flux, and its addition can improve the problems of poor solid crystallinity and long preparation time. Good crystallinity can also further improve the comprehensive performance of the material. Moreover, the method of the present invention is simple to operate, low in cost, and more environmentally friendly.

[0028] (2) The sodium titanium phosphate anode material provided by the present invention has good conductivity. Sodium-ion batteries prepared using the sodium titanium phosphate anode material of the present invention have high specific capacity, good rate performance and good cycle stability. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 These are XRD comparison images of the negative electrode materials prepared in Example 1 and Comparative Examples 1-6 of this invention;

[0031] Figure 2 This is a comparison chart of the rate performance of Example 1 and Comparative Examples 1, 3, 5 and 6 of the present invention. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0033] The first aspect of the present invention provides a method for preparing sodium titanium phosphate anode material, comprising the following steps:

[0034] The sodium titanium phosphate anode material is obtained by mixing phosphorus source, sodium source, titanium source, mixed carbon source and boron source and sintering in an inert atmosphere; wherein the mixed carbon source includes at least two different carbon sources, and as an example, the inert atmosphere can be an argon atmosphere or a nitrogen atmosphere.

[0035] This invention addresses the problems of low electrochemical activity, poor electronic conductivity, high cost and poor effect of atomic doping, cumbersome preparation process, and poor crystallinity in solid-state preparation of sodium titanium phosphate. It utilizes the different conductivity of different carbon sources and employs a mixed carbon source containing at least two different carbon sources for carbon coating to improve the electronic conductivity of sodium titanium phosphate, thereby enhancing coulombic efficiency and rate performance. The addition of a boron source can improve the stability of the material itself, making it less prone to side reactions, thus improving its electrochemical performance. The boron source can also act as a flux, improving the problems of poor solid-state crystallinity and long preparation time. Good crystallinity can further improve the overall performance of the material. Moreover, this invention uses a solid-state preparation method, which is simple to operate, low in cost, and more environmentally friendly.

[0036] In some specific embodiments of the present invention, the phosphorus source, the sodium source, and the titanium source are measured according to a P:Na:Ti molar ratio of 2.5-3.5:1:1.5-2.5. For example, the P:Na:Ti molar ratio can be any one value or a range of any two values ​​from 2.5:1:1.5, 2.5:1:2, 2.5:1:2.5, 3:1:1.5, 3:1:2, 3:1:2.5, 3.5:1:1.5, 3.5:1:2, 3.5:1:2.5.

[0037] In some specific embodiments of the present invention, the amount of boron source added accounts for 1wt%-10wt% of the total mass of all raw materials, for example, any one value or a range of any two values ​​from 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, to 10wt%. The addition of boron source can first improve the stability of the material itself and avoid or reduce the occurrence of side reactions. Secondly, boron source also acts as a flux, which can improve the problem of poor crystallinity in solid-state methods, thereby improving the electrochemical performance of sodium titanium phosphate.

[0038] In some specific embodiments of the present invention, the amount of the mixed carbon source added is measured according to its theoretical carbon content (the mass of carbon element in the mixed carbon source) accounting for 1wt%-10wt% of the total mass of all raw materials. For example, the theoretical carbon content of the added carbon source can be any value or a range of any two values ​​from 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, and 10wt% of the total mass of the raw materials. Too little carbon source will not achieve the purpose of improving conductivity, while too much carbon source will lead to an excessively thick coating layer, incomplete capacity utilization, reduced energy density, and affected sodium ion transport. Therefore, it is necessary to reasonably control the amount of carbon source used.

[0039] In some specific embodiments of the present invention, the boron source includes boric acid and / or boron oxide, wherein the boric acid is converted into boron oxide during sintering and co-coated with the mixed carbon source.

[0040] In some specific embodiments of the present invention, the mixed carbon source includes at least two of graphite, glucose, sucrose, citric acid, starch, graphene, and carbon nanofibers. Different carbon sources have different conductivity. Using a mixed carbon source composed of two or more different carbon sources for coating is more effective in improving the conductivity of sodium titanium phosphate anode material and the electrochemical performance of the battery compared with coating with a single carbon source.

[0041] In some specific embodiments of the present invention, the mixed carbon source includes graphite and glucose.

[0042] In some specific embodiments of the present invention, the theoretical carbon content (carbon in glucose) of the graphite and the glucose is in the range of 6:1 to 1:2, for example, any one value or any two values ​​in the range of 6:1, 5:1, 4:1, 3:1, 2:1, 3:2, 1:1, 2:3, 1:2. If the mass ratio of carbon in graphite and glucose is too large or too small, the overall performance of the material will decrease.

[0043] In some specific embodiments of the present invention, the phosphorus source includes at least one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, ammonium phosphate, and diammonium hydrogen phosphate.

[0044] In some specific embodiments of the present invention, the sodium source includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, sodium carbonate, sodium bicarbonate, and sodium acetate, wherein sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium phosphate can be used as both phosphorus and sodium sources.

[0045] In some specific embodiments of the present invention, the titanium source includes at least one of titanium dioxide, metatitanic acid, and titanium trioxide.

[0046] In some specific embodiments of the present invention, the mixing is ball milling. Ball milling can improve the uniformity of mixing and refine the grains, which is beneficial for the full coating of sodium titanium phosphate after sintering and improves the electrochemical performance of the material.

[0047] In some specific embodiments of the present invention, the rotational speed of the ball mill is 200-1000 r / min, for example, any one value or a range of any two values ​​among 200 r / min, 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min, 900 r / min, and 1000 r / min, and the ball milling time is 1-15 h, for example, any one value or a range of any two values ​​among 1 h, 3 h, 5 h, 7 h, 9 h, 11 h, 13 h, and 15 h.

[0048] Properly controlling the ball milling speed and time can improve the uniformity of the mixing of reaction raw materials, and at the same time, ensure that the reaction raw materials have a suitable particle size.

[0049] In some specific embodiments of the present invention, the sintering temperature is 500-1000℃, for example, any one value or a range of any two values ​​among 500℃, 600℃, 700℃, 800℃, 900℃, 950℃, and 1000℃. Too high or too low a sintering temperature will affect the electrochemical performance of the product. The sintering time is 1-6h, for example, any one value or a range of any two values ​​among 1h, 2h, 3h, 4h, 5h, and 6h.

[0050] In some specific embodiments of the present invention, the heating rate of the sintering is 1-10℃ / min, for example, any one value or a range of any two values ​​from 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, and 10℃ / min. If the heating rate is too fast or too slow, it will affect the crystallinity and thus the electrochemical performance of the material. Therefore, it is necessary to reasonably control the heating rate.

[0051] A sodium titanium phosphate anode material is prepared by the method for preparing sodium titanium phosphate anode material as described in any of the preceding embodiments.

[0052] A sodium-ion battery comprising the negative electrode material as described above.

[0053] The sodium-ion battery has high capacity, good rate performance, and good cycle stability.

[0054] The following detailed description of some embodiments of the present invention is provided in conjunction with specific examples. Unless otherwise specified, all raw materials used in the embodiments are commercially available.

[0055] Example 1

[0056] Diammonium hydrogen phosphate, sodium dihydrogen phosphate, and titanium dioxide were weighed in a stoichiometric ratio of 2:1:2. Graphite, glucose, and boric acid were added, with graphite accounting for 4 wt% of the total mass of all raw materials. The theoretical carbon content of the added glucose accounted for 1 wt% of the total mass of all raw materials (the mass of carbon in the added glucose accounted for 1 wt% of the total mass of the raw materials). Boric acid accounted for 5 wt% of the total mass of all raw materials. The mixture was ball-milled for 10 hours at a speed of 700 r / min, and the temperature was increased to 800℃ at a rate of 5℃ / min. The mixture was then sintered for 3 hours under an argon atmosphere to obtain sodium titanium phosphate anode material.

[0057] Example 2

[0058] Example 2 is similar to Example 1, except that in Example 2 the temperature is increased to 800°C at a rate of 2°C / min, and the other conditions are the same as in Example 1, which will not be repeated here.

[0059] Example 3

[0060] Example 3 is similar to Example 1, except that in Example 3 the temperature is increased to 800°C at a rate of 8°C / min, and the other conditions are the same as in Example 1, which will not be repeated here.

[0061] Example 4

[0062] Example 4 is similar to Example 1, except that: in Example 4, the amount of graphite added accounts for 4.2 wt% of the total mass of all raw materials, and the theoretical carbon content of the added glucose accounts for 0.8 wt% of the total mass of all raw materials. The other conditions are the same as in Example 1, and will not be repeated here.

[0063] Example 5

[0064] Example 5 is similar to Example 1, except that: in Example 5, the amount of graphite added accounts for 2 wt% of the total mass of all raw materials, and the theoretical carbon content of the added grapes accounts for 3 wt% of the total mass of all raw materials. The other conditions are the same as in Example 1, and will not be repeated here.

[0065] Example 6

[0066] Example 6 is similar to Example 1, except that in Example 6 the temperature is increased to 500°C at a rate of 5°C / min, and the other conditions are the same as in Example 1, which will not be repeated here.

[0067] Example 7

[0068] Example 7 is similar to Example 1, except that in Example 7 the temperature is increased to 950°C at a rate of 5°C / min, and the other conditions are the same as in Example 1, which will not be repeated here.

[0069] Example 8

[0070] Example 8 is similar to Example 1, except that the amount of boric acid added in Example 8 accounts for 3 wt% of the total mass of all raw materials, and the other conditions are the same as in Example 1, which will not be repeated here.

[0071] Example 9

[0072] Example 9 is similar to Example 1, except that the amount of boric acid added in Example 9 accounts for 8 wt% of the total mass of all raw materials, and the other conditions are the same as in Example 1, which will not be repeated here.

[0073] Comparative Example 1

[0074] Comparative Example 1 is similar to Example 1, except that: no graphite and glucose are added to Comparative Example 1, only boric acid is added, and the amount of boric acid added is 5 wt% of the total mass of all raw materials. The other conditions are the same as in Example 1.

[0075] Comparative Example 2

[0076] Comparative Example 2 is similar to Example 1, except that: no graphite and boric acid are added to Comparative Example 2, only glucose is added, and the theoretical carbon content of the added glucose accounts for 5 wt% of the total mass of all raw materials. The other conditions are the same as in Example 1.

[0077] Comparative Example 3

[0078] Comparative Example 3 is similar to Example 1, except that: no glucose and boric acid are added to Comparative Example 3, only graphite is added, and the amount of graphite added is 5 wt% of the total mass of all raw materials. The other conditions are the same as in Example 1.

[0079] Comparative Example 4

[0080] Comparative Example 4 is similar to Example 1, except that: no boric acid is added to Comparative Example 4, only glucose and graphite are added. The amount of graphite added is 4 wt% of the total mass of all raw materials, and the theoretical carbon content of the added glucose accounts for 1 wt% of the total mass of all raw materials. The other conditions are the same as in Example 1.

[0081] Comparative Example 5

[0082] Comparative Example 5 is similar to Example 1, except that: no graphite is added to Comparative Example 5, only boric acid and glucose are added. The theoretical carbon content of the added glucose accounts for 5 wt% of the total mass of all raw materials, and the amount of added boric acid accounts for 5 wt% of the total mass of all raw materials. The other conditions are the same as in Example 1.

[0083] Comparative Example 6

[0084] Comparative Example 6 is similar to Example 1, except that boric acid, glucose and graphite are not added to Comparative Example 6, and the other conditions are the same as in Example 1.

[0085] Experimental Example

[0086] 1. XRD tests were performed on the sodium titanium phosphate anode materials prepared in each embodiment and each comparative example. The results are as follows: Figure 1 As shown, the structure of sodium titanium phosphate remained unchanged after the addition of one or more of boric acid, graphite, and glucose.

[0087] 2. Battery assembly and electrochemical performance testing

[0088] (1) Preparation of positive electrode sheet: The positive electrode active material: conductive agent: binder = 8:1:1 is used to make slurry. First, 25mg of PVDF is weighed and put into a weighing bottle, and 800μL of NMP is added dropwise. The bottle is sealed with plastic wrap and stirred with a magnetic stirrer for 6h. After stirring, the plastic wrap is opened and 200mg of positive electrode active material and 25mg of Super P are added and stirred together for 6h. The slurry is evenly coated on stainless steel foil using a coating machine. After coating, it is placed in a 90℃ vacuum drying oven and dried for 6h. After drying, it is taken out and cut into sheets using a cutting machine to obtain the positive electrode sheet.

[0089] (2) Preparation of negative electrode sheet: The negative electrode active material: conductive agent: binder = 8:1:1 is used to make slurry. First, 25mg of PVDF is weighed and put into a weighing bottle, and 800μL of NMP is added dropwise. The bottle is sealed with plastic wrap and stirred with a magnetic stirrer for 6h. After stirring, the plastic wrap is opened and 200mg of negative electrode active material and 25mg of Super P are added and stirred together for 6h. The slurry is evenly coated on copper foil using a coating machine. After coating, it is placed in a 90℃ vacuum drying oven and dried for 6h. After drying, it is taken out and cut into sheets using a cutting machine to obtain the negative electrode sheet.

[0090] (3) Battery assembly: The battery case model 2025, the electrolyte is 17mol / kg sodium perchlorate, and the separator is glass fiber for full battery assembly.

[0091] Electrochemical performance tests were conducted on the sodium titanium phosphate anode materials prepared in each embodiment and each comparative example, as well as the batteries assembled using the sodium titanium phosphate anode materials in each embodiment and each comparative example. The only difference between the batteries was the anode material used; all other conditions were the same.

[0092] The specific capacity was tested using a three-electrode method with an electrochemical workstation. The voltage range for specific capacity testing was -1V to -0.4V, and the current density was 64mA / g. The rate performance and cycle performance of the full cell were tested. The voltage range for full cell testing was 0 to 2V, and the current density was 64mA / g. The test results are shown in Table 1.

[0093] Table 1

[0094]

[0095]

[0096] As shown in Table 1, compared with sodium titanium phosphate anode materials prepared by single boron source coating, single carbon source coating, mixed carbon source coating, and co-coating of boron source and single carbon source, the sodium titanium phosphate anode material prepared by co-coating of boron source and mixed carbon source has better performance. The charge and discharge specific capacity, first efficiency, and cycle stability of the sodium titanium phosphate anode material prepared by co-coating of boron source and mixed carbon source in this invention are significantly improved.

[0097] Depend on Figure 2 It can be seen that the rate performance of the sodium titanium phosphate anode material prepared by the method of the present invention has also been significantly improved.

[0098] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a sodium titanium phosphate anode material, characterized in that, Includes the following steps: The sodium titanium phosphate anode material is obtained by mixing phosphorus source, sodium source, titanium source, mixed carbon source and boron source and sintering in an inert atmosphere; wherein, the mixed carbon source includes at least two different carbon sources, the boron source includes boric acid, and the boric acid is converted into boron oxide during sintering and co-coated with the mixed carbon source.

2. The method for preparing sodium titanium phosphate anode material according to claim 1, characterized in that, The phosphorus source, the sodium source, and the titanium source are measured in a P:Na:Ti molar ratio of 2.5-3.5:1:1.5-2.

5.

3. The method for preparing sodium titanium phosphate anode material according to claim 1, characterized in that, The amount of boron source added accounts for 1wt%-10wt% of the total mass of all raw materials.

4. The method for preparing sodium titanium phosphate anode material according to claim 1, characterized in that, The amount of the mixed carbon source added is measured as 1wt%-10wt% of the theoretical carbon content of all raw materials.

5. The method for preparing sodium titanium phosphate anode material according to claim 1, characterized in that, The mixed carbon source includes at least two of graphite, glucose, sucrose, citric acid, starch, graphene, and carbon nanofibers.

6. The method for preparing sodium titanium phosphate anode material according to claim 5, characterized in that, The mixed carbon source includes graphite and glucose.

7. The method for preparing sodium titanium phosphate anode material according to claim 6, characterized in that, The theoretical carbon content mass ratio of the graphite and the glucose is 6:1 to 1:

2.

8. The method for preparing sodium titanium phosphate anode material according to claim 1, characterized in that, It includes at least one of the following features (1) to (3): (1) The phosphorus source includes at least one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, ammonium phosphate, and diammonium hydrogen phosphate; (2) The sodium source includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, sodium carbonate, sodium bicarbonate, and sodium acetate; (3) The titanium source includes at least one of titanium dioxide, metatitanic acid, and titanium trioxide.

9. The method for preparing sodium titanium phosphate anode material according to claim 1, characterized in that, It includes at least one of the following features (1) to (3): (1) The mixing is ball milling; (2) The sintering temperature is 500-1000℃, and the sintering time is 1-6h; (3) The heating rate of the sintering is 1-10℃ / min.

10. A sodium titanium phosphate anode material, characterized in that, The sodium titanium phosphate anode material was prepared using the preparation method described in any one of claims 1-9.

11. A sodium-ion battery, characterized in that, Includes the negative electrode material as described in claim 10.

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